Import zlib from GCC

11 files changed, 4801 insertions, 0 deletions

diff --git a/zlib/examples/README.examples b/zlib/examples/README.examples
new file mode 100644
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--- /dev/null
+++ b/zlib/examples/README.examples
@@ -0,0 +1,49 @@
+This directory contains examples of the use of zlib and other relevant
+programs and documentation.
+
+enough.c
+    calculation and justification of ENOUGH parameter in inftrees.h
+    - calculates the maximum table space used in inflate tree
+      construction over all possible Huffman codes
+
+fitblk.c
+    compress just enough input to nearly fill a requested output size
+    - zlib isn't designed to do this, but fitblk does it anyway
+
+gun.c
+    uncompress a gzip file
+    - illustrates the use of inflateBack() for high speed file-to-file
+      decompression using call-back functions
+    - is approximately twice as fast as gzip -d
+    - also provides Unix uncompress functionality, again twice as fast
+
+gzappend.c
+    append to a gzip file
+    - illustrates the use of the Z_BLOCK flush parameter for inflate()
+    - illustrates the use of deflatePrime() to start at any bit
+
+gzjoin.c
+    join gzip files without recalculating the crc or recompressing
+    - illustrates the use of the Z_BLOCK flush parameter for inflate()
+    - illustrates the use of crc32_combine()
+
+gzlog.c
+gzlog.h
+    efficiently and robustly maintain a message log file in gzip format
+    - illustrates use of raw deflate, Z_PARTIAL_FLUSH, deflatePrime(),
+      and deflateSetDictionary()
+    - illustrates use of a gzip header extra field
+
+zlib_how.html
+    painfully comprehensive description of zpipe.c (see below)
+    - describes in excruciating detail the use of deflate() and inflate()
+
+zpipe.c
+    reads and writes zlib streams from stdin to stdout
+    - illustrates the proper use of deflate() and inflate()
+    - deeply commented in zlib_how.html (see above)
+
+zran.c
+    index a zlib or gzip stream and randomly access it
+    - illustrates the use of Z_BLOCK, inflatePrime(), and
+      inflateSetDictionary() to provide random access
diff --git a/zlib/examples/enough.c b/zlib/examples/enough.c
new file mode 100644
index 0000000..c40410b
--- /dev/null
+++ b/zlib/examples/enough.c
@@ -0,0 +1,569 @@
+/* enough.c -- determine the maximum size of inflate's Huffman code tables over
+ * all possible valid and complete Huffman codes, subject to a length limit.
+ * Copyright (C) 2007, 2008 Mark Adler
+ * Version 1.3  17 February 2008  Mark Adler
+ */
+
+/* Version history:
+   1.0   3 Jan 2007  First version (derived from codecount.c version 1.4)
+   1.1   4 Jan 2007  Use faster incremental table usage computation
+                     Prune examine() search on previously visited states
+   1.2   5 Jan 2007  Comments clean up
+                     As inflate does, decrease root for short codes
+                     Refuse cases where inflate would increase root
+   1.3  17 Feb 2008  Add argument for initial root table size
+                     Fix bug for initial root table size == max - 1
+                     Use a macro to compute the history index
+ */
+
+/*
+   Examine all possible Huffman codes for a given number of symbols and a
+   maximum code length in bits to determine the maximum table size for zilb's
+   inflate.  Only complete Huffman codes are counted.
+
+   Two codes are considered distinct if the vectors of the number of codes per
+   length are not identical.  So permutations of the symbol assignments result
+   in the same code for the counting, as do permutations of the assignments of
+   the bit values to the codes (i.e. only canonical codes are counted).
+
+   We build a code from shorter to longer lengths, determining how many symbols
+   are coded at each length.  At each step, we have how many symbols remain to
+   be coded, what the last code length used was, and how many bit patterns of
+   that length remain unused. Then we add one to the code length and double the
+   number of unused patterns to graduate to the next code length.  We then
+   assign all portions of the remaining symbols to that code length that
+   preserve the properties of a correct and eventually complete code.  Those
+   properties are: we cannot use more bit patterns than are available; and when
+   all the symbols are used, there are exactly zero possible bit patterns
+   remaining.
+
+   The inflate Huffman decoding algorithm uses two-level lookup tables for
+   speed.  There is a single first-level table to decode codes up to root bits
+   in length (root == 9 in the current inflate implementation).  The table
+   has 1 << root entries and is indexed by the next root bits of input.  Codes
+   shorter than root bits have replicated table entries, so that the correct
+   entry is pointed to regardless of the bits that follow the short code.  If
+   the code is longer than root bits, then the table entry points to a second-
+   level table.  The size of that table is determined by the longest code with
+   that root-bit prefix.  If that longest code has length len, then the table
+   has size 1 << (len - root), to index the remaining bits in that set of
+   codes.  Each subsequent root-bit prefix then has its own sub-table.  The
+   total number of table entries required by the code is calculated
+   incrementally as the number of codes at each bit length is populated.  When
+   all of the codes are shorter than root bits, then root is reduced to the
+   longest code length, resulting in a single, smaller, one-level table.
+
+   The inflate algorithm also provides for small values of root (relative to
+   the log2 of the number of symbols), where the shortest code has more bits
+   than root.  In that case, root is increased to the length of the shortest
+   code.  This program, by design, does not handle that case, so it is verified
+   that the number of symbols is less than 2^(root + 1).
+
+   In order to speed up the examination (by about ten orders of magnitude for
+   the default arguments), the intermediate states in the build-up of a code
+   are remembered and previously visited branches are pruned.  The memory
+   required for this will increase rapidly with the total number of symbols and
+   the maximum code length in bits.  However this is a very small price to pay
+   for the vast speedup.
+
+   First, all of the possible Huffman codes are counted, and reachable
+   intermediate states are noted by a non-zero count in a saved-results array.
+   Second, the intermediate states that lead to (root + 1) bit or longer codes
+   are used to look at all sub-codes from those junctures for their inflate
+   memory usage.  (The amount of memory used is not affected by the number of
+   codes of root bits or less in length.)  Third, the visited states in the
+   construction of those sub-codes and the associated calculation of the table
+   size is recalled in order to avoid recalculating from the same juncture.
+   Beginning the code examination at (root + 1) bit codes, which is enabled by
+   identifying the reachable nodes, accounts for about six of the orders of
+   magnitude of improvement for the default arguments.  About another four
+   orders of magnitude come from not revisiting previous states.  Out of
+   approximately 2x10^16 possible Huffman codes, only about 2x10^6 sub-codes
+   need to be examined to cover all of the possible table memory usage cases
+   for the default arguments of 286 symbols limited to 15-bit codes.
+
+   Note that an unsigned long long type is used for counting.  It is quite easy
+   to exceed the capacity of an eight-byte integer with a large number of
+   symbols and a large maximum code length, so multiple-precision arithmetic
+   would need to replace the unsigned long long arithmetic in that case.  This
+   program will abort if an overflow occurs.  The big_t type identifies where
+   the counting takes place.
+
+   An unsigned long long type is also used for calculating the number of
+   possible codes remaining at the maximum length.  This limits the maximum
+   code length to the number of bits in a long long minus the number of bits
+   needed to represent the symbols in a flat code.  The code_t type identifies
+   where the bit pattern counting takes place.
+ */
+
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <assert.h>
+
+#define local static
+
+/* special data types */
+typedef unsigned long long big_t;   /* type for code counting */
+typedef unsigned long long code_t;  /* type for bit pattern counting */
+struct tab {                        /* type for been here check */
+    size_t len;         /* length of bit vector in char's */
+    char *vec;          /* allocated bit vector */
+};
+
+/* The array for saving results, num[], is indexed with this triplet:
+
+      syms: number of symbols remaining to code
+      left: number of available bit patterns at length len
+      len: number of bits in the codes currently being assigned
+
+   Those indices are constrained thusly when saving results:
+
+      syms: 3..totsym (totsym == total symbols to code)
+      left: 2..syms - 1, but only the evens (so syms == 8 -> 2, 4, 6)
+      len: 1..max - 1 (max == maximum code length in bits)
+
+   syms == 2 is not saved since that immediately leads to a single code.  left
+   must be even, since it represents the number of available bit patterns at
+   the current length, which is double the number at the previous length.
+   left ends at syms-1 since left == syms immediately results in a single code.
+   (left > sym is not allowed since that would result in an incomplete code.)
+   len is less than max, since the code completes immediately when len == max.
+
+   The offset into the array is calculated for the three indices with the
+   first one (syms) being outermost, and the last one (len) being innermost.
+   We build the array with length max-1 lists for the len index, with syms-3
+   of those for each symbol.  There are totsym-2 of those, with each one
+   varying in length as a function of sym.  See the calculation of index in
+   count() for the index, and the calculation of size in main() for the size
+   of the array.
+
+   For the deflate example of 286 symbols limited to 15-bit codes, the array
+   has 284,284 entries, taking up 2.17 MB for an 8-byte big_t.  More than
+   half of the space allocated for saved results is actually used -- not all
+   possible triplets are reached in the generation of valid Huffman codes.
+ */
+
+/* The array for tracking visited states, done[], is itself indexed identically
+   to the num[] array as described above for the (syms, left, len) triplet.
+   Each element in the array is further indexed by the (mem, rem) doublet,
+   where mem is the amount of inflate table space used so far, and rem is the
+   remaining unused entries in the current inflate sub-table.  Each indexed
+   element is simply one bit indicating whether the state has been visited or
+   not.  Since the ranges for mem and rem are not known a priori, each bit
+   vector is of a variable size, and grows as needed to accommodate the visited
+   states.  mem and rem are used to calculate a single index in a triangular
+   array.  Since the range of mem is expected in the default case to be about
+   ten times larger than the range of rem, the array is skewed to reduce the
+   memory usage, with eight times the range for mem than for rem.  See the
+   calculations for offset and bit in beenhere() for the details.
+
+   For the deflate example of 286 symbols limited to 15-bit codes, the bit
+   vectors grow to total approximately 21 MB, in addition to the 4.3 MB done[]
+   array itself.
+ */
+
+/* Globals to avoid propagating constants or constant pointers recursively */
+local int max;          /* maximum allowed bit length for the codes */
+local int root;         /* size of base code table in bits */
+local int large;        /* largest code table so far */
+local size_t size;      /* number of elements in num and done */
+local int *code;        /* number of symbols assigned to each bit length */
+local big_t *num;       /* saved results array for code counting */
+local struct tab *done; /* states already evaluated array */
+
+/* Index function for num[] and done[] */
+#define INDEX(i,j,k) (((size_t)((i-1)>>1)*((i-2)>>1)+(j>>1)-1)*(max-1)+k-1)
+
+/* Free allocated space.  Uses globals code, num, and done. */
+local void cleanup(void)
+{
+    size_t n;
+
+    if (done != NULL) {
+        for (n = 0; n < size; n++)
+            if (done[n].len)
+                free(done[n].vec);
+        free(done);
+    }
+    if (num != NULL)
+        free(num);
+    if (code != NULL)
+        free(code);
+}
+
+/* Return the number of possible Huffman codes using bit patterns of lengths
+   len through max inclusive, coding syms symbols, with left bit patterns of
+   length len unused -- return -1 if there is an overflow in the counting.
+   Keep a record of previous results in num to prevent repeating the same
+   calculation.  Uses the globals max and num. */
+local big_t count(int syms, int len, int left)
+{
+    big_t sum;          /* number of possible codes from this juncture */
+    big_t got;          /* value returned from count() */
+    int least;          /* least number of syms to use at this juncture */
+    int most;           /* most number of syms to use at this juncture */
+    int use;            /* number of bit patterns to use in next call */
+    size_t index;       /* index of this case in *num */
+
+    /* see if only one possible code */
+    if (syms == left)
+        return 1;
+
+    /* note and verify the expected state */
+    assert(syms > left && left > 0 && len < max);
+
+    /* see if we've done this one already */
+    index = INDEX(syms, left, len);
+    got = num[index];
+    if (got)
+        return got;         /* we have -- return the saved result */
+
+    /* we need to use at least this many bit patterns so that the code won't be
+       incomplete at the next length (more bit patterns than symbols) */
+    least = (left << 1) - syms;
+    if (least < 0)
+        least = 0;
+
+    /* we can use at most this many bit patterns, lest there not be enough
+       available for the remaining symbols at the maximum length (if there were
+       no limit to the code length, this would become: most = left - 1) */
+    most = (((code_t)left << (max - len)) - syms) /
+            (((code_t)1 << (max - len)) - 1);
+
+    /* count all possible codes from this juncture and add them up */
+    sum = 0;
+    for (use = least; use <= most; use++) {
+        got = count(syms - use, len + 1, (left - use) << 1);
+        sum += got;
+        if (got == -1 || sum < got)         /* overflow */
+            return -1;
+    }
+
+    /* verify that all recursive calls are productive */
+    assert(sum != 0);
+
+    /* save the result and return it */
+    num[index] = sum;
+    return sum;
+}
+
+/* Return true if we've been here before, set to true if not.  Set a bit in a
+   bit vector to indicate visiting this state.  Each (syms,len,left) state
+   has a variable size bit vector indexed by (mem,rem).  The bit vector is
+   lengthened if needed to allow setting the (mem,rem) bit. */
+local int beenhere(int syms, int len, int left, int mem, int rem)
+{
+    size_t index;       /* index for this state's bit vector */
+    size_t offset;      /* offset in this state's bit vector */
+    int bit;            /* mask for this state's bit */
+    size_t length;      /* length of the bit vector in bytes */
+    char *vector;       /* new or enlarged bit vector */
+
+    /* point to vector for (syms,left,len), bit in vector for (mem,rem) */
+    index = INDEX(syms, left, len);
+    mem -= 1 << root;
+    offset = (mem >> 3) + rem;
+    offset = ((offset * (offset + 1)) >> 1) + rem;
+    bit = 1 << (mem & 7);
+
+    /* see if we've been here */
+    length = done[index].len;
+    if (offset < length && (done[index].vec[offset] & bit) != 0)
+        return 1;       /* done this! */
+
+    /* we haven't been here before -- set the bit to show we have now */
+
+    /* see if we need to lengthen the vector in order to set the bit */
+    if (length <= offset) {
+        /* if we have one already, enlarge it, zero out the appended space */
+        if (length) {
+            do {
+                length <<= 1;
+            } while (length <= offset);
+            vector = realloc(done[index].vec, length);
+            if (vector != NULL)
+                memset(vector + done[index].len, 0, length - done[index].len);
+        }
+
+        /* otherwise we need to make a new vector and zero it out */
+        else {
+            length = 1 << (len - root);
+            while (length <= offset)
+                length <<= 1;
+            vector = calloc(length, sizeof(char));
+        }
+
+        /* in either case, bail if we can't get the memory */
+        if (vector == NULL) {
+            fputs("abort: unable to allocate enough memory\n", stderr);
+            cleanup();
+            exit(1);
+        }
+
+        /* install the new vector */
+        done[index].len = length;
+        done[index].vec = vector;
+    }
+
+    /* set the bit */
+    done[index].vec[offset] |= bit;
+    return 0;
+}
+
+/* Examine all possible codes from the given node (syms, len, left).  Compute
+   the amount of memory required to build inflate's decoding tables, where the
+   number of code structures used so far is mem, and the number remaining in
+   the current sub-table is rem.  Uses the globals max, code, root, large, and
+   done. */
+local void examine(int syms, int len, int left, int mem, int rem)
+{
+    int least;          /* least number of syms to use at this juncture */
+    int most;           /* most number of syms to use at this juncture */
+    int use;            /* number of bit patterns to use in next call */
+
+    /* see if we have a complete code */
+    if (syms == left) {
+        /* set the last code entry */
+        code[len] = left;
+
+        /* complete computation of memory used by this code */
+        while (rem < left) {
+            left -= rem;
+            rem = 1 << (len - root);
+            mem += rem;
+        }
+        assert(rem == left);
+
+        /* if this is a new maximum, show the entries used and the sub-code */
+        if (mem > large) {
+            large = mem;
+            printf("max %d: ", mem);
+            for (use = root + 1; use <= max; use++)
+                if (code[use])
+                    printf("%d[%d] ", code[use], use);
+            putchar('\n');
+            fflush(stdout);
+        }
+
+        /* remove entries as we drop back down in the recursion */
+        code[len] = 0;
+        return;
+    }
+
+    /* prune the tree if we can */
+    if (beenhere(syms, len, left, mem, rem))
+        return;
+
+    /* we need to use at least this many bit patterns so that the code won't be
+       incomplete at the next length (more bit patterns than symbols) */
+    least = (left << 1) - syms;
+    if (least < 0)
+        least = 0;
+
+    /* we can use at most this many bit patterns, lest there not be enough
+       available for the remaining symbols at the maximum length (if there were
+       no limit to the code length, this would become: most = left - 1) */
+    most = (((code_t)left << (max - len)) - syms) /
+            (((code_t)1 << (max - len)) - 1);
+
+    /* occupy least table spaces, creating new sub-tables as needed */
+    use = least;
+    while (rem < use) {
+        use -= rem;
+        rem = 1 << (len - root);
+        mem += rem;
+    }
+    rem -= use;
+
+    /* examine codes from here, updating table space as we go */
+    for (use = least; use <= most; use++) {
+        code[len] = use;
+        examine(syms - use, len + 1, (left - use) << 1,
+                mem + (rem ? 1 << (len - root) : 0), rem << 1);
+        if (rem == 0) {
+            rem = 1 << (len - root);
+            mem += rem;
+        }
+        rem--;
+    }
+
+    /* remove entries as we drop back down in the recursion */
+    code[len] = 0;
+}
+
+/* Look at all sub-codes starting with root + 1 bits.  Look at only the valid
+   intermediate code states (syms, left, len).  For each completed code,
+   calculate the amount of memory required by inflate to build the decoding
+   tables. Find the maximum amount of memory required and show the code that
+   requires that maximum.  Uses the globals max, root, and num. */
+local void enough(int syms)
+{
+    int n;              /* number of remaing symbols for this node */
+    int left;           /* number of unused bit patterns at this length */
+    size_t index;       /* index of this case in *num */
+
+    /* clear code */
+    for (n = 0; n <= max; n++)
+        code[n] = 0;
+
+    /* look at all (root + 1) bit and longer codes */
+    large = 1 << root;              /* base table */
+    if (root < max)                 /* otherwise, there's only a base table */
+        for (n = 3; n <= syms; n++)
+            for (left = 2; left < n; left += 2)
+            {
+                /* look at all reachable (root + 1) bit nodes, and the
+                   resulting codes (complete at root + 2 or more) */
+                index = INDEX(n, left, root + 1);
+                if (root + 1 < max && num[index])       /* reachable node */
+                    examine(n, root + 1, left, 1 << root, 0);
+
+                /* also look at root bit codes with completions at root + 1
+                   bits (not saved in num, since complete), just in case */
+                if (num[index - 1] && n <= left << 1)
+                    examine((n - left) << 1, root + 1, (n - left) << 1,
+                            1 << root, 0);
+            }
+
+    /* done */
+    printf("done: maximum of %d table entries\n", large);
+}
+
+/*
+   Examine and show the total number of possible Huffman codes for a given
+   maximum number of symbols, initial root table size, and maximum code length
+   in bits -- those are the command arguments in that order.  The default
+   values are 286, 9, and 15 respectively, for the deflate literal/length code.
+   The possible codes are counted for each number of coded symbols from two to
+   the maximum.  The counts for each of those and the total number of codes are
+   shown.  The maximum number of inflate table entires is then calculated
+   across all possible codes.  Each new maximum number of table entries and the
+   associated sub-code (starting at root + 1 == 10 bits) is shown.
+
+   To count and examine Huffman codes that are not length-limited, provide a
+   maximum length equal to the number of symbols minus one.
+
+   For the deflate literal/length code, use "enough".  For the deflate distance
+   code, use "enough 30 6".
+
+   This uses the %llu printf format to print big_t numbers, which assumes that
+   big_t is an unsigned long long.  If the big_t type is changed (for example
+   to a multiple precision type), the method of printing will also need to be
+   updated.
+ */
+int main(int argc, char **argv)
+{
+    int syms;           /* total number of symbols to code */
+    int n;              /* number of symbols to code for this run */
+    big_t got;          /* return value of count() */
+    big_t sum;          /* accumulated number of codes over n */
+
+    /* set up globals for cleanup() */
+    code = NULL;
+    num = NULL;
+    done = NULL;
+
+    /* get arguments -- default to the deflate literal/length code */
+    syms = 286;
+        root = 9;
+    max = 15;
+    if (argc > 1) {
+        syms = atoi(argv[1]);
+        if (argc > 2) {
+            root = atoi(argv[2]);
+                        if (argc > 3)
+                                max = atoi(argv[3]);
+                }
+    }
+    if (argc > 4 || syms < 2 || root < 1 || max < 1) {
+        fputs("invalid arguments, need: [sym >= 2 [root >= 1 [max >= 1]]]\n",
+                          stderr);
+        return 1;
+    }
+
+    /* if not restricting the code length, the longest is syms - 1 */
+    if (max > syms - 1)
+        max = syms - 1;
+
+    /* determine the number of bits in a code_t */
+    n = 0;
+    while (((code_t)1 << n) != 0)
+        n++;
+
+    /* make sure that the calculation of most will not overflow */
+    if (max > n || syms - 2 >= (((code_t)0 - 1) >> (max - 1))) {
+        fputs("abort: code length too long for internal types\n", stderr);
+        return 1;
+    }
+
+    /* reject impossible code requests */
+    if (syms - 1 > ((code_t)1 << max) - 1) {
+        fprintf(stderr, "%d symbols cannot be coded in %d bits\n",
+                syms, max);
+        return 1;
+    }
+
+    /* allocate code vector */
+    code = calloc(max + 1, sizeof(int));
+    if (code == NULL) {
+        fputs("abort: unable to allocate enough memory\n", stderr);
+        return 1;
+    }
+
+    /* determine size of saved results array, checking for overflows,
+       allocate and clear the array (set all to zero with calloc()) */
+    if (syms == 2)              /* iff max == 1 */
+        num = NULL;             /* won't be saving any results */
+    else {
+        size = syms >> 1;
+        if (size > ((size_t)0 - 1) / (n = (syms - 1) >> 1) ||
+                (size *= n, size > ((size_t)0 - 1) / (n = max - 1)) ||
+                (size *= n, size > ((size_t)0 - 1) / sizeof(big_t)) ||
+                (num = calloc(size, sizeof(big_t))) == NULL) {
+            fputs("abort: unable to allocate enough memory\n", stderr);
+            cleanup();
+            return 1;
+        }
+    }
+
+    /* count possible codes for all numbers of symbols, add up counts */
+    sum = 0;
+    for (n = 2; n <= syms; n++) {
+        got = count(n, 1, 2);
+        sum += got;
+        if (got == -1 || sum < got) {       /* overflow */
+            fputs("abort: can't count that high!\n", stderr);
+            cleanup();
+            return 1;
+        }
+        printf("%llu %d-codes\n", got, n);
+    }
+    printf("%llu total codes for 2 to %d symbols", sum, syms);
+    if (max < syms - 1)
+        printf(" (%d-bit length limit)\n", max);
+    else
+        puts(" (no length limit)");
+
+    /* allocate and clear done array for beenhere() */
+    if (syms == 2)
+        done = NULL;
+    else if (size > ((size_t)0 - 1) / sizeof(struct tab) ||
+             (done = calloc(size, sizeof(struct tab))) == NULL) {
+        fputs("abort: unable to allocate enough memory\n", stderr);
+        cleanup();
+        return 1;
+    }
+
+    /* find and show maximum inflate table usage */
+        if (root > max)                 /* reduce root to max length */
+                root = max;
+    if (syms < ((code_t)1 << (root + 1)))
+        enough(syms);
+    else
+        puts("cannot handle minimum code lengths > root");
+
+    /* done */
+    cleanup();
+    return 0;
+}
diff --git a/zlib/examples/fitblk.c b/zlib/examples/fitblk.c
new file mode 100644
index 0000000..c61de5c
--- /dev/null
+++ b/zlib/examples/fitblk.c
@@ -0,0 +1,233 @@
+/* fitblk.c: example of fitting compressed output to a specified size
+   Not copyrighted -- provided to the public domain
+   Version 1.1  25 November 2004  Mark Adler */
+
+/* Version history:
+   1.0  24 Nov 2004  First version
+   1.1  25 Nov 2004  Change deflateInit2() to deflateInit()
+                     Use fixed-size, stack-allocated raw buffers
+                     Simplify code moving compression to subroutines
+                     Use assert() for internal errors
+                     Add detailed description of approach
+ */
+
+/* Approach to just fitting a requested compressed size:
+
+   fitblk performs three compression passes on a portion of the input
+   data in order to determine how much of that input will compress to
+   nearly the requested output block size.  The first pass generates
+   enough deflate blocks to produce output to fill the requested
+   output size plus a specfied excess amount (see the EXCESS define
+   below).  The last deflate block may go quite a bit past that, but
+   is discarded.  The second pass decompresses and recompresses just
+   the compressed data that fit in the requested plus excess sized
+   buffer.  The deflate process is terminated after that amount of
+   input, which is less than the amount consumed on the first pass.
+   The last deflate block of the result will be of a comparable size
+   to the final product, so that the header for that deflate block and
+   the compression ratio for that block will be about the same as in
+   the final product.  The third compression pass decompresses the
+   result of the second step, but only the compressed data up to the
+   requested size minus an amount to allow the compressed stream to
+   complete (see the MARGIN define below).  That will result in a
+   final compressed stream whose length is less than or equal to the
+   requested size.  Assuming sufficient input and a requested size
+   greater than a few hundred bytes, the shortfall will typically be
+   less than ten bytes.
+
+   If the input is short enough that the first compression completes
+   before filling the requested output size, then that compressed
+   stream is return with no recompression.
+
+   EXCESS is chosen to be just greater than the shortfall seen in a
+   two pass approach similar to the above.  That shortfall is due to
+   the last deflate block compressing more efficiently with a smaller
+   header on the second pass.  EXCESS is set to be large enough so
+   that there is enough uncompressed data for the second pass to fill
+   out the requested size, and small enough so that the final deflate
+   block of the second pass will be close in size to the final deflate
+   block of the third and final pass.  MARGIN is chosen to be just
+   large enough to assure that the final compression has enough room
+   to complete in all cases.
+ */
+
+#include <stdio.h>
+#include <stdlib.h>
+#include <assert.h>
+#include "zlib.h"
+
+#define local static
+
+/* print nastygram and leave */
+local void quit(char *why)
+{
+    fprintf(stderr, "fitblk abort: %s\n", why);
+    exit(1);
+}
+
+#define RAWLEN 4096    /* intermediate uncompressed buffer size */
+
+/* compress from file to def until provided buffer is full or end of
+   input reached; return last deflate() return value, or Z_ERRNO if
+   there was read error on the file */
+local int partcompress(FILE *in, z_streamp def)
+{
+    int ret, flush;
+    unsigned char raw[RAWLEN];
+
+    flush = Z_NO_FLUSH;
+    do {
+        def->avail_in = fread(raw, 1, RAWLEN, in);
+        if (ferror(in))
+            return Z_ERRNO;
+        def->next_in = raw;
+        if (feof(in))
+            flush = Z_FINISH;
+        ret = deflate(def, flush);
+        assert(ret != Z_STREAM_ERROR);
+    } while (def->avail_out != 0 && flush == Z_NO_FLUSH);
+    return ret;
+}
+
+/* recompress from inf's input to def's output; the input for inf and
+   the output for def are set in those structures before calling;
+   return last deflate() return value, or Z_MEM_ERROR if inflate()
+   was not able to allocate enough memory when it needed to */
+local int recompress(z_streamp inf, z_streamp def)
+{
+    int ret, flush;
+    unsigned char raw[RAWLEN];
+
+    flush = Z_NO_FLUSH;
+    do {
+        /* decompress */
+        inf->avail_out = RAWLEN;
+        inf->next_out = raw;
+        ret = inflate(inf, Z_NO_FLUSH);
+        assert(ret != Z_STREAM_ERROR && ret != Z_DATA_ERROR &&
+               ret != Z_NEED_DICT);
+        if (ret == Z_MEM_ERROR)
+            return ret;
+
+        /* compress what was decompresed until done or no room */
+        def->avail_in = RAWLEN - inf->avail_out;
+        def->next_in = raw;
+        if (inf->avail_out != 0)
+            flush = Z_FINISH;
+        ret = deflate(def, flush);
+        assert(ret != Z_STREAM_ERROR);
+    } while (ret != Z_STREAM_END && def->avail_out != 0);
+    return ret;
+}
+
+#define EXCESS 256      /* empirically determined stream overage */
+#define MARGIN 8        /* amount to back off for completion */
+
+/* compress from stdin to fixed-size block on stdout */
+int main(int argc, char **argv)
+{
+    int ret;                /* return code */
+    unsigned size;          /* requested fixed output block size */
+    unsigned have;          /* bytes written by deflate() call */
+    unsigned char *blk;     /* intermediate and final stream */
+    unsigned char *tmp;     /* close to desired size stream */
+    z_stream def, inf;      /* zlib deflate and inflate states */
+
+    /* get requested output size */
+    if (argc != 2)
+        quit("need one argument: size of output block");
+    ret = strtol(argv[1], argv + 1, 10);
+    if (argv[1][0] != 0)
+        quit("argument must be a number");
+    if (ret < 8)            /* 8 is minimum zlib stream size */
+        quit("need positive size of 8 or greater");
+    size = (unsigned)ret;
+
+    /* allocate memory for buffers and compression engine */
+    blk = malloc(size + EXCESS);
+    def.zalloc = Z_NULL;
+    def.zfree = Z_NULL;
+    def.opaque = Z_NULL;
+    ret = deflateInit(&def, Z_DEFAULT_COMPRESSION);
+    if (ret != Z_OK || blk == NULL)
+        quit("out of memory");
+
+    /* compress from stdin until output full, or no more input */
+    def.avail_out = size + EXCESS;
+    def.next_out = blk;
+    ret = partcompress(stdin, &def);
+    if (ret == Z_ERRNO)
+        quit("error reading input");
+
+    /* if it all fit, then size was undersubscribed -- done! */
+    if (ret == Z_STREAM_END && def.avail_out >= EXCESS) {
+        /* write block to stdout */
+        have = size + EXCESS - def.avail_out;
+        if (fwrite(blk, 1, have, stdout) != have || ferror(stdout))
+            quit("error writing output");
+
+        /* clean up and print results to stderr */
+        ret = deflateEnd(&def);
+        assert(ret != Z_STREAM_ERROR);
+        free(blk);
+        fprintf(stderr,
+                "%u bytes unused out of %u requested (all input)\n",
+                size - have, size);
+        return 0;
+    }
+
+    /* it didn't all fit -- set up for recompression */
+    inf.zalloc = Z_NULL;
+    inf.zfree = Z_NULL;
+    inf.opaque = Z_NULL;
+    inf.avail_in = 0;
+    inf.next_in = Z_NULL;
+    ret = inflateInit(&inf);
+    tmp = malloc(size + EXCESS);
+    if (ret != Z_OK || tmp == NULL)
+        quit("out of memory");
+    ret = deflateReset(&def);
+    assert(ret != Z_STREAM_ERROR);
+
+    /* do first recompression close to the right amount */
+    inf.avail_in = size + EXCESS;
+    inf.next_in = blk;
+    def.avail_out = size + EXCESS;
+    def.next_out = tmp;
+    ret = recompress(&inf, &def);
+    if (ret == Z_MEM_ERROR)
+        quit("out of memory");
+
+    /* set up for next reocmpression */
+    ret = inflateReset(&inf);
+    assert(ret != Z_STREAM_ERROR);
+    ret = deflateReset(&def);
+    assert(ret != Z_STREAM_ERROR);
+
+    /* do second and final recompression (third compression) */
+    inf.avail_in = size - MARGIN;   /* assure stream will complete */
+    inf.next_in = tmp;
+    def.avail_out = size;
+    def.next_out = blk;
+    ret = recompress(&inf, &def);
+    if (ret == Z_MEM_ERROR)
+        quit("out of memory");
+    assert(ret == Z_STREAM_END);    /* otherwise MARGIN too small */
+
+    /* done -- write block to stdout */
+    have = size - def.avail_out;
+    if (fwrite(blk, 1, have, stdout) != have || ferror(stdout))
+        quit("error writing output");
+
+    /* clean up and print results to stderr */
+    free(tmp);
+    ret = inflateEnd(&inf);
+    assert(ret != Z_STREAM_ERROR);
+    ret = deflateEnd(&def);
+    assert(ret != Z_STREAM_ERROR);
+    free(blk);
+    fprintf(stderr,
+            "%u bytes unused out of %u requested (%lu input)\n",
+            size - have, size, def.total_in);
+    return 0;
+}
diff --git a/zlib/examples/gun.c b/zlib/examples/gun.c
new file mode 100644
index 0000000..72b0882
--- /dev/null
+++ b/zlib/examples/gun.c
@@ -0,0 +1,701 @@
+/* gun.c -- simple gunzip to give an example of the use of inflateBack()
+ * Copyright (C) 2003, 2005, 2008, 2010 Mark Adler
+ * For conditions of distribution and use, see copyright notice in zlib.h
+   Version 1.6  17 January 2010  Mark Adler */
+
+/* Version history:
+   1.0  16 Feb 2003  First version for testing of inflateBack()
+   1.1  21 Feb 2005  Decompress concatenated gzip streams
+                     Remove use of "this" variable (C++ keyword)
+                     Fix return value for in()
+                     Improve allocation failure checking
+                     Add typecasting for void * structures
+                     Add -h option for command version and usage
+                     Add a bunch of comments
+   1.2  20 Mar 2005  Add Unix compress (LZW) decompression
+                     Copy file attributes from input file to output file
+   1.3  12 Jun 2005  Add casts for error messages [Oberhumer]
+   1.4   8 Dec 2006  LZW decompression speed improvements
+   1.5   9 Feb 2008  Avoid warning in latest version of gcc
+   1.6  17 Jan 2010  Avoid signed/unsigned comparison warnings
+ */
+
+/*
+   gun [ -t ] [ name ... ]
+
+   decompresses the data in the named gzip files.  If no arguments are given,
+   gun will decompress from stdin to stdout.  The names must end in .gz, -gz,
+   .z, -z, _z, or .Z.  The uncompressed data will be written to a file name
+   with the suffix stripped.  On success, the original file is deleted.  On
+   failure, the output file is deleted.  For most failures, the command will
+   continue to process the remaining names on the command line.  A memory
+   allocation failure will abort the command.  If -t is specified, then the
+   listed files or stdin will be tested as gzip files for integrity (without
+   checking for a proper suffix), no output will be written, and no files
+   will be deleted.
+
+   Like gzip, gun allows concatenated gzip streams and will decompress them,
+   writing all of the uncompressed data to the output.  Unlike gzip, gun allows
+   an empty file on input, and will produce no error writing an empty output
+   file.
+
+   gun will also decompress files made by Unix compress, which uses LZW
+   compression.  These files are automatically detected by virtue of their
+   magic header bytes.  Since the end of Unix compress stream is marked by the
+   end-of-file, they cannot be concantenated.  If a Unix compress stream is
+   encountered in an input file, it is the last stream in that file.
+
+   Like gunzip and uncompress, the file attributes of the orignal compressed
+   file are maintained in the final uncompressed file, to the extent that the
+   user permissions allow it.
+
+   On my Mac OS X PowerPC G4, gun is almost twice as fast as gunzip (version
+   1.2.4) is on the same file, when gun is linked with zlib 1.2.2.  Also the
+   LZW decompression provided by gun is about twice as fast as the standard
+   Unix uncompress command.
+ */
+
+/* external functions and related types and constants */
+#include <stdio.h>          /* fprintf() */
+#include <stdlib.h>         /* malloc(), free() */
+#include <string.h>         /* strerror(), strcmp(), strlen(), memcpy() */
+#include <errno.h>          /* errno */
+#include <fcntl.h>          /* open() */
+#include <unistd.h>         /* read(), write(), close(), chown(), unlink() */
+#include <sys/types.h>
+#include <sys/stat.h>       /* stat(), chmod() */
+#include <utime.h>          /* utime() */
+#include "zlib.h"           /* inflateBackInit(), inflateBack(), */
+                            /* inflateBackEnd(), crc32() */
+
+/* function declaration */
+#define local static
+
+/* buffer constants */
+#define SIZE 32768U         /* input and output buffer sizes */
+#define PIECE 16384         /* limits i/o chunks for 16-bit int case */
+
+/* structure for infback() to pass to input function in() -- it maintains the
+   input file and a buffer of size SIZE */
+struct ind {
+    int infile;
+    unsigned char *inbuf;
+};
+
+/* Load input buffer, assumed to be empty, and return bytes loaded and a
+   pointer to them.  read() is called until the buffer is full, or until it
+   returns end-of-file or error.  Return 0 on error. */
+local unsigned in(void *in_desc, unsigned char **buf)
+{
+    int ret;
+    unsigned len;
+    unsigned char *next;
+    struct ind *me = (struct ind *)in_desc;
+
+    next = me->inbuf;
+    *buf = next;
+    len = 0;
+    do {
+        ret = PIECE;
+        if ((unsigned)ret > SIZE - len)
+            ret = (int)(SIZE - len);
+        ret = (int)read(me->infile, next, ret);
+        if (ret == -1) {
+            len = 0;
+            break;
+        }
+        next += ret;
+        len += ret;
+    } while (ret != 0 && len < SIZE);
+    return len;
+}
+
+/* structure for infback() to pass to output function out() -- it maintains the
+   output file, a running CRC-32 check on the output and the total number of
+   bytes output, both for checking against the gzip trailer.  (The length in
+   the gzip trailer is stored modulo 2^32, so it's ok if a long is 32 bits and
+   the output is greater than 4 GB.) */
+struct outd {
+    int outfile;
+    int check;                  /* true if checking crc and total */
+    unsigned long crc;
+    unsigned long total;
+};
+
+/* Write output buffer and update the CRC-32 and total bytes written.  write()
+   is called until all of the output is written or an error is encountered.
+   On success out() returns 0.  For a write failure, out() returns 1.  If the
+   output file descriptor is -1, then nothing is written.
+ */
+local int out(void *out_desc, unsigned char *buf, unsigned len)
+{
+    int ret;
+    struct outd *me = (struct outd *)out_desc;
+
+    if (me->check) {
+        me->crc = crc32(me->crc, buf, len);
+        me->total += len;
+    }
+    if (me->outfile != -1)
+        do {
+            ret = PIECE;
+            if ((unsigned)ret > len)
+                ret = (int)len;
+            ret = (int)write(me->outfile, buf, ret);
+            if (ret == -1)
+                return 1;
+            buf += ret;
+            len -= ret;
+        } while (len != 0);
+    return 0;
+}
+
+/* next input byte macro for use inside lunpipe() and gunpipe() */
+#define NEXT() (have ? 0 : (have = in(indp, &next)), \
+                last = have ? (have--, (int)(*next++)) : -1)
+
+/* memory for gunpipe() and lunpipe() --
+   the first 256 entries of prefix[] and suffix[] are never used, could
+   have offset the index, but it's faster to waste the memory */
+unsigned char inbuf[SIZE];              /* input buffer */
+unsigned char outbuf[SIZE];             /* output buffer */
+unsigned short prefix[65536];           /* index to LZW prefix string */
+unsigned char suffix[65536];            /* one-character LZW suffix */
+unsigned char match[65280 + 2];         /* buffer for reversed match or gzip
+                                           32K sliding window */
+
+/* throw out what's left in the current bits byte buffer (this is a vestigial
+   aspect of the compressed data format derived from an implementation that
+   made use of a special VAX machine instruction!) */
+#define FLUSHCODE() \
+    do { \
+        left = 0; \
+        rem = 0; \
+        if (chunk > have) { \
+            chunk -= have; \
+            have = 0; \
+            if (NEXT() == -1) \
+                break; \
+            chunk--; \
+            if (chunk > have) { \
+                chunk = have = 0; \
+                break; \
+            } \
+        } \
+        have -= chunk; \
+        next += chunk; \
+        chunk = 0; \
+    } while (0)
+
+/* Decompress a compress (LZW) file from indp to outfile.  The compress magic
+   header (two bytes) has already been read and verified.  There are have bytes
+   of buffered input at next.  strm is used for passing error information back
+   to gunpipe().
+
+   lunpipe() will return Z_OK on success, Z_BUF_ERROR for an unexpected end of
+   file, read error, or write error (a write error indicated by strm->next_in
+   not equal to Z_NULL), or Z_DATA_ERROR for invalid input.
+ */
+local int lunpipe(unsigned have, unsigned char *next, struct ind *indp,
+                  int outfile, z_stream *strm)
+{
+    int last;                   /* last byte read by NEXT(), or -1 if EOF */
+    unsigned chunk;             /* bytes left in current chunk */
+    int left;                   /* bits left in rem */
+    unsigned rem;               /* unused bits from input */
+    int bits;                   /* current bits per code */
+    unsigned code;              /* code, table traversal index */
+    unsigned mask;              /* mask for current bits codes */
+    int max;                    /* maximum bits per code for this stream */
+    unsigned flags;             /* compress flags, then block compress flag */
+    unsigned end;               /* last valid entry in prefix/suffix tables */
+    unsigned temp;              /* current code */
+    unsigned prev;              /* previous code */
+    unsigned final;             /* last character written for previous code */
+    unsigned stack;             /* next position for reversed string */
+    unsigned outcnt;            /* bytes in output buffer */
+    struct outd outd;           /* output structure */
+    unsigned char *p;
+
+    /* set up output */
+    outd.outfile = outfile;
+    outd.check = 0;
+
+    /* process remainder of compress header -- a flags byte */
+    flags = NEXT();
+    if (last == -1)
+        return Z_BUF_ERROR;
+    if (flags & 0x60) {
+        strm->msg = (char *)"unknown lzw flags set";
+        return Z_DATA_ERROR;
+    }
+    max = flags & 0x1f;
+    if (max < 9 || max > 16) {
+        strm->msg = (char *)"lzw bits out of range";
+        return Z_DATA_ERROR;
+    }
+    if (max == 9)                           /* 9 doesn't really mean 9 */
+        max = 10;
+    flags &= 0x80;                          /* true if block compress */
+
+    /* clear table */
+    bits = 9;
+    mask = 0x1ff;
+    end = flags ? 256 : 255;
+
+    /* set up: get first 9-bit code, which is the first decompressed byte, but
+       don't create a table entry until the next code */
+    if (NEXT() == -1)                       /* no compressed data is ok */
+        return Z_OK;
+    final = prev = (unsigned)last;          /* low 8 bits of code */
+    if (NEXT() == -1)                       /* missing a bit */
+        return Z_BUF_ERROR;
+    if (last & 1) {                         /* code must be < 256 */
+        strm->msg = (char *)"invalid lzw code";
+        return Z_DATA_ERROR;
+    }
+    rem = (unsigned)last >> 1;              /* remaining 7 bits */
+    left = 7;
+    chunk = bits - 2;                       /* 7 bytes left in this chunk */
+    outbuf[0] = (unsigned char)final;       /* write first decompressed byte */
+    outcnt = 1;
+
+    /* decode codes */
+    stack = 0;
+    for (;;) {
+        /* if the table will be full after this, increment the code size */
+        if (end >= mask && bits < max) {
+            FLUSHCODE();
+            bits++;
+            mask <<= 1;
+            mask++;
+        }
+
+        /* get a code of length bits */
+        if (chunk == 0)                     /* decrement chunk modulo bits */
+            chunk = bits;
+        code = rem;                         /* low bits of code */
+        if (NEXT() == -1) {                 /* EOF is end of compressed data */
+            /* write remaining buffered output */
+            if (outcnt && out(&outd, outbuf, outcnt)) {
+                strm->next_in = outbuf;     /* signal write error */
+                return Z_BUF_ERROR;
+            }
+            return Z_OK;
+        }
+        code += (unsigned)last << left;     /* middle (or high) bits of code */
+        left += 8;
+        chunk--;
+        if (bits > left) {                  /* need more bits */
+            if (NEXT() == -1)               /* can't end in middle of code */
+                return Z_BUF_ERROR;
+            code += (unsigned)last << left; /* high bits of code */
+            left += 8;
+            chunk--;
+        }
+        code &= mask;                       /* mask to current code length */
+        left -= bits;                       /* number of unused bits */
+        rem = (unsigned)last >> (8 - left); /* unused bits from last byte */
+
+        /* process clear code (256) */
+        if (code == 256 && flags) {
+            FLUSHCODE();
+            bits = 9;                       /* initialize bits and mask */
+            mask = 0x1ff;
+            end = 255;                      /* empty table */
+            continue;                       /* get next code */
+        }
+
+        /* special code to reuse last match */
+        temp = code;                        /* save the current code */
+        if (code > end) {
+            /* Be picky on the allowed code here, and make sure that the code
+               we drop through (prev) will be a valid index so that random
+               input does not cause an exception.  The code != end + 1 check is
+               empirically derived, and not checked in the original uncompress
+               code.  If this ever causes a problem, that check could be safely
+               removed.  Leaving this check in greatly improves gun's ability
+               to detect random or corrupted input after a compress header.
+               In any case, the prev > end check must be retained. */
+            if (code != end + 1 || prev > end) {
+                strm->msg = (char *)"invalid lzw code";
+                return Z_DATA_ERROR;
+            }
+            match[stack++] = (unsigned char)final;
+            code = prev;
+        }
+
+        /* walk through linked list to generate output in reverse order */
+        p = match + stack;
+        while (code >= 256) {
+            *p++ = suffix[code];
+            code = prefix[code];
+        }
+        stack = p - match;
+        match[stack++] = (unsigned char)code;
+        final = code;
+
+        /* link new table entry */
+        if (end < mask) {
+            end++;
+            prefix[end] = (unsigned short)prev;
+            suffix[end] = (unsigned char)final;
+        }
+
+        /* set previous code for next iteration */
+        prev = temp;
+
+        /* write output in forward order */
+        while (stack > SIZE - outcnt) {
+            while (outcnt < SIZE)
+                outbuf[outcnt++] = match[--stack];
+            if (out(&outd, outbuf, outcnt)) {
+                strm->next_in = outbuf; /* signal write error */
+                return Z_BUF_ERROR;
+            }
+            outcnt = 0;
+        }
+        p = match + stack;
+        do {
+            outbuf[outcnt++] = *--p;
+        } while (p > match);
+        stack = 0;
+
+        /* loop for next code with final and prev as the last match, rem and
+           left provide the first 0..7 bits of the next code, end is the last
+           valid table entry */
+    }
+}
+
+/* Decompress a gzip file from infile to outfile.  strm is assumed to have been
+   successfully initialized with inflateBackInit().  The input file may consist
+   of a series of gzip streams, in which case all of them will be decompressed
+   to the output file.  If outfile is -1, then the gzip stream(s) integrity is
+   checked and nothing is written.
+
+   The return value is a zlib error code: Z_MEM_ERROR if out of memory,
+   Z_DATA_ERROR if the header or the compressed data is invalid, or if the
+   trailer CRC-32 check or length doesn't match, Z_BUF_ERROR if the input ends
+   prematurely or a write error occurs, or Z_ERRNO if junk (not a another gzip
+   stream) follows a valid gzip stream.
+ */
+local int gunpipe(z_stream *strm, int infile, int outfile)
+{
+    int ret, first, last;
+    unsigned have, flags, len;
+    unsigned char *next = NULL;
+    struct ind ind, *indp;
+    struct outd outd;
+
+    /* setup input buffer */
+    ind.infile = infile;
+    ind.inbuf = inbuf;
+    indp = &ind;
+
+    /* decompress concatenated gzip streams */
+    have = 0;                               /* no input data read in yet */
+    first = 1;                              /* looking for first gzip header */
+    strm->next_in = Z_NULL;                 /* so Z_BUF_ERROR means EOF */
+    for (;;) {
+        /* look for the two magic header bytes for a gzip stream */
+        if (NEXT() == -1) {
+            ret = Z_OK;
+            break;                          /* empty gzip stream is ok */
+        }
+        if (last != 31 || (NEXT() != 139 && last != 157)) {
+            strm->msg = (char *)"incorrect header check";
+            ret = first ? Z_DATA_ERROR : Z_ERRNO;
+            break;                          /* not a gzip or compress header */
+        }
+        first = 0;                          /* next non-header is junk */
+
+        /* process a compress (LZW) file -- can't be concatenated after this */
+        if (last == 157) {
+            ret = lunpipe(have, next, indp, outfile, strm);
+            break;
+        }
+
+        /* process remainder of gzip header */
+        ret = Z_BUF_ERROR;
+        if (NEXT() != 8) {                  /* only deflate method allowed */
+            if (last == -1) break;
+            strm->msg = (char *)"unknown compression method";
+            ret = Z_DATA_ERROR;
+            break;
+        }
+        flags = NEXT();                     /* header flags */
+        NEXT();                             /* discard mod time, xflgs, os */
+        NEXT();
+        NEXT();
+        NEXT();
+        NEXT();
+        NEXT();
+        if (last == -1) break;
+        if (flags & 0xe0) {
+            strm->msg = (char *)"unknown header flags set";
+            ret = Z_DATA_ERROR;
+            break;
+        }
+        if (flags & 4) {                    /* extra field */
+            len = NEXT();
+            len += (unsigned)(NEXT()) << 8;
+            if (last == -1) break;
+            while (len > have) {
+                len -= have;
+                have = 0;
+                if (NEXT() == -1) break;
+                len--;
+            }
+            if (last == -1) break;
+            have -= len;
+            next += len;
+        }
+        if (flags & 8)                      /* file name */
+            while (NEXT() != 0 && last != -1)
+                ;
+        if (flags & 16)                     /* comment */
+            while (NEXT() != 0 && last != -1)
+                ;
+        if (flags & 2) {                    /* header crc */
+            NEXT();
+            NEXT();
+        }
+        if (last == -1) break;
+
+        /* set up output */
+        outd.outfile = outfile;
+        outd.check = 1;
+        outd.crc = crc32(0L, Z_NULL, 0);
+        outd.total = 0;
+
+        /* decompress data to output */
+        strm->next_in = next;
+        strm->avail_in = have;
+        ret = inflateBack(strm, in, indp, out, &outd);
+        if (ret != Z_STREAM_END) break;
+        next = strm->next_in;
+        have = strm->avail_in;
+        strm->next_in = Z_NULL;             /* so Z_BUF_ERROR means EOF */
+
+        /* check trailer */
+        ret = Z_BUF_ERROR;
+        if (NEXT() != (int)(outd.crc & 0xff) ||
+            NEXT() != (int)((outd.crc >> 8) & 0xff) ||
+            NEXT() != (int)((outd.crc >> 16) & 0xff) ||
+            NEXT() != (int)((outd.crc >> 24) & 0xff)) {
+            /* crc error */
+            if (last != -1) {
+                strm->msg = (char *)"incorrect data check";
+                ret = Z_DATA_ERROR;
+            }
+            break;
+        }
+        if (NEXT() != (int)(outd.total & 0xff) ||
+            NEXT() != (int)((outd.total >> 8) & 0xff) ||
+            NEXT() != (int)((outd.total >> 16) & 0xff) ||
+            NEXT() != (int)((outd.total >> 24) & 0xff)) {
+            /* length error */
+            if (last != -1) {
+                strm->msg = (char *)"incorrect length check";
+                ret = Z_DATA_ERROR;
+            }
+            break;
+        }
+
+        /* go back and look for another gzip stream */
+    }
+
+    /* clean up and return */
+    return ret;
+}
+
+/* Copy file attributes, from -> to, as best we can.  This is best effort, so
+   no errors are reported.  The mode bits, including suid, sgid, and the sticky
+   bit are copied (if allowed), the owner's user id and group id are copied
+   (again if allowed), and the access and modify times are copied. */
+local void copymeta(char *from, char *to)
+{
+    struct stat was;
+    struct utimbuf when;
+
+    /* get all of from's Unix meta data, return if not a regular file */
+    if (stat(from, &was) != 0 || (was.st_mode & S_IFMT) != S_IFREG)
+        return;
+
+    /* set to's mode bits, ignore errors */
+    (void)chmod(to, was.st_mode & 07777);
+
+    /* copy owner's user and group, ignore errors */
+    (void)chown(to, was.st_uid, was.st_gid);
+
+    /* copy access and modify times, ignore errors */
+    when.actime = was.st_atime;
+    when.modtime = was.st_mtime;
+    (void)utime(to, &when);
+}
+
+/* Decompress the file inname to the file outnname, of if test is true, just
+   decompress without writing and check the gzip trailer for integrity.  If
+   inname is NULL or an empty string, read from stdin.  If outname is NULL or
+   an empty string, write to stdout.  strm is a pre-initialized inflateBack
+   structure.  When appropriate, copy the file attributes from inname to
+   outname.
+
+   gunzip() returns 1 if there is an out-of-memory error or an unexpected
+   return code from gunpipe().  Otherwise it returns 0.
+ */
+local int gunzip(z_stream *strm, char *inname, char *outname, int test)
+{
+    int ret;
+    int infile, outfile;
+
+    /* open files */
+    if (inname == NULL || *inname == 0) {
+        inname = "-";
+        infile = 0;     /* stdin */
+    }
+    else {
+        infile = open(inname, O_RDONLY, 0);
+        if (infile == -1) {
+            fprintf(stderr, "gun cannot open %s\n", inname);
+            return 0;
+        }
+    }
+    if (test)
+        outfile = -1;
+    else if (outname == NULL || *outname == 0) {
+        outname = "-";
+        outfile = 1;    /* stdout */
+    }
+    else {
+        outfile = open(outname, O_CREAT | O_TRUNC | O_WRONLY, 0666);
+        if (outfile == -1) {
+            close(infile);
+            fprintf(stderr, "gun cannot create %s\n", outname);
+            return 0;
+        }
+    }
+    errno = 0;
+
+    /* decompress */
+    ret = gunpipe(strm, infile, outfile);
+    if (outfile > 2) close(outfile);
+    if (infile > 2) close(infile);
+
+    /* interpret result */
+    switch (ret) {
+    case Z_OK:
+    case Z_ERRNO:
+        if (infile > 2 && outfile > 2) {
+            copymeta(inname, outname);          /* copy attributes */
+            unlink(inname);
+        }
+        if (ret == Z_ERRNO)
+            fprintf(stderr, "gun warning: trailing garbage ignored in %s\n",
+                    inname);
+        break;
+    case Z_DATA_ERROR:
+        if (outfile > 2) unlink(outname);
+        fprintf(stderr, "gun data error on %s: %s\n", inname, strm->msg);
+        break;
+    case Z_MEM_ERROR:
+        if (outfile > 2) unlink(outname);
+        fprintf(stderr, "gun out of memory error--aborting\n");
+        return 1;
+    case Z_BUF_ERROR:
+        if (outfile > 2) unlink(outname);
+        if (strm->next_in != Z_NULL) {
+            fprintf(stderr, "gun write error on %s: %s\n",
+                    outname, strerror(errno));
+        }
+        else if (errno) {
+            fprintf(stderr, "gun read error on %s: %s\n",
+                    inname, strerror(errno));
+        }
+        else {
+            fprintf(stderr, "gun unexpected end of file on %s\n",
+                    inname);
+        }
+        break;
+    default:
+        if (outfile > 2) unlink(outname);
+        fprintf(stderr, "gun internal error--aborting\n");
+        return 1;
+    }
+    return 0;
+}
+
+/* Process the gun command line arguments.  See the command syntax near the
+   beginning of this source file. */
+int main(int argc, char **argv)
+{
+    int ret, len, test;
+    char *outname;
+    unsigned char *window;
+    z_stream strm;
+
+    /* initialize inflateBack state for repeated use */
+    window = match;                         /* reuse LZW match buffer */
+    strm.zalloc = Z_NULL;
+    strm.zfree = Z_NULL;
+    strm.opaque = Z_NULL;
+    ret = inflateBackInit(&strm, 15, window);
+    if (ret != Z_OK) {
+        fprintf(stderr, "gun out of memory error--aborting\n");
+        return 1;
+    }
+
+    /* decompress each file to the same name with the suffix removed */
+    argc--;
+    argv++;
+    test = 0;
+    if (argc && strcmp(*argv, "-h") == 0) {
+        fprintf(stderr, "gun 1.6 (17 Jan 2010)\n");
+        fprintf(stderr, "Copyright (C) 2003-2010 Mark Adler\n");
+        fprintf(stderr, "usage: gun [-t] [file1.gz [file2.Z ...]]\n");
+        return 0;
+    }
+    if (argc && strcmp(*argv, "-t") == 0) {
+        test = 1;
+        argc--;
+        argv++;
+    }
+    if (argc)
+        do {
+            if (test)
+                outname = NULL;
+            else {
+                len = (int)strlen(*argv);
+                if (strcmp(*argv + len - 3, ".gz") == 0 ||
+                    strcmp(*argv + len - 3, "-gz") == 0)
+                    len -= 3;
+                else if (strcmp(*argv + len - 2, ".z") == 0 ||
+                    strcmp(*argv + len - 2, "-z") == 0 ||
+                    strcmp(*argv + len - 2, "_z") == 0 ||
+                    strcmp(*argv + len - 2, ".Z") == 0)
+                    len -= 2;
+                else {
+                    fprintf(stderr, "gun error: no gz type on %s--skipping\n",
+                            *argv);
+                    continue;
+                }
+                outname = malloc(len + 1);
+                if (outname == NULL) {
+                    fprintf(stderr, "gun out of memory error--aborting\n");
+                    ret = 1;
+                    break;
+                }
+                memcpy(outname, *argv, len);
+                outname[len] = 0;
+            }
+            ret = gunzip(&strm, *argv, outname, test);
+            if (outname != NULL) free(outname);
+            if (ret) break;
+        } while (argv++, --argc);
+    else
+        ret = gunzip(&strm, NULL, NULL, test);
+
+    /* clean up */
+    inflateBackEnd(&strm);
+    return ret;
+}
diff --git a/zlib/examples/gzappend.c b/zlib/examples/gzappend.c
new file mode 100644
index 0000000..e9e878e
--- /dev/null
+++ b/zlib/examples/gzappend.c
@@ -0,0 +1,500 @@
+/* gzappend -- command to append to a gzip file
+
+  Copyright (C) 2003 Mark Adler, all rights reserved
+  version 1.1, 4 Nov 2003
+
+  This software is provided 'as-is', without any express or implied
+  warranty.  In no event will the author be held liable for any damages
+  arising from the use of this software.
+
+  Permission is granted to anyone to use this software for any purpose,
+  including commercial applications, and to alter it and redistribute it
+  freely, subject to the following restrictions:
+
+  1. The origin of this software must not be misrepresented; you must not
+     claim that you wrote the original software. If you use this software
+     in a product, an acknowledgment in the product documentation would be
+     appreciated but is not required.
+  2. Altered source versions must be plainly marked as such, and must not be
+     misrepresented as being the original software.
+  3. This notice may not be removed or altered from any source distribution.
+
+  Mark Adler    madler@alumni.caltech.edu
+ */
+
+/*
+ * Change history:
+ *
+ * 1.0  19 Oct 2003     - First version
+ * 1.1   4 Nov 2003     - Expand and clarify some comments and notes
+ *                      - Add version and copyright to help
+ *                      - Send help to stdout instead of stderr
+ *                      - Add some preemptive typecasts
+ *                      - Add L to constants in lseek() calls
+ *                      - Remove some debugging information in error messages
+ *                      - Use new data_type definition for zlib 1.2.1
+ *                      - Simplfy and unify file operations
+ *                      - Finish off gzip file in gztack()
+ *                      - Use deflatePrime() instead of adding empty blocks
+ *                      - Keep gzip file clean on appended file read errors
+ *                      - Use in-place rotate instead of auxiliary buffer
+ *                        (Why you ask?  Because it was fun to write!)
+ */
+
+/*
+   gzappend takes a gzip file and appends to it, compressing files from the
+   command line or data from stdin.  The gzip file is written to directly, to
+   avoid copying that file, in case it's large.  Note that this results in the
+   unfriendly behavior that if gzappend fails, the gzip file is corrupted.
+
+   This program was written to illustrate the use of the new Z_BLOCK option of
+   zlib 1.2.x's inflate() function.  This option returns from inflate() at each
+   block boundary to facilitate locating and modifying the last block bit at
+   the start of the final deflate block.  Also whether using Z_BLOCK or not,
+   another required feature of zlib 1.2.x is that inflate() now provides the
+   number of unusued bits in the last input byte used.  gzappend will not work
+   with versions of zlib earlier than 1.2.1.
+
+   gzappend first decompresses the gzip file internally, discarding all but
+   the last 32K of uncompressed data, and noting the location of the last block
+   bit and the number of unused bits in the last byte of the compressed data.
+   The gzip trailer containing the CRC-32 and length of the uncompressed data
+   is verified.  This trailer will be later overwritten.
+
+   Then the last block bit is cleared by seeking back in the file and rewriting
+   the byte that contains it.  Seeking forward, the last byte of the compressed
+   data is saved along with the number of unused bits to initialize deflate.
+
+   A deflate process is initialized, using the last 32K of the uncompressed
+   data from the gzip file to initialize the dictionary.  If the total
+   uncompressed data was less than 32K, then all of it is used to initialize
+   the dictionary.  The deflate output bit buffer is also initialized with the
+   last bits from the original deflate stream.  From here on, the data to
+   append is simply compressed using deflate, and written to the gzip file.
+   When that is complete, the new CRC-32 and uncompressed length are written
+   as the trailer of the gzip file.
+ */
+
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <fcntl.h>
+#include <unistd.h>
+#include "zlib.h"
+
+#define local static
+#define LGCHUNK 14
+#define CHUNK (1U << LGCHUNK)
+#define DSIZE 32768U
+
+/* print an error message and terminate with extreme prejudice */
+local void bye(char *msg1, char *msg2)
+{
+    fprintf(stderr, "gzappend error: %s%s\n", msg1, msg2);
+    exit(1);
+}
+
+/* return the greatest common divisor of a and b using Euclid's algorithm,
+   modified to be fast when one argument much greater than the other, and
+   coded to avoid unnecessary swapping */
+local unsigned gcd(unsigned a, unsigned b)
+{
+    unsigned c;
+
+    while (a && b)
+        if (a > b) {
+            c = b;
+            while (a - c >= c)
+                c <<= 1;
+            a -= c;
+        }
+        else {
+            c = a;
+            while (b - c >= c)
+                c <<= 1;
+            b -= c;
+        }
+    return a + b;
+}
+
+/* rotate list[0..len-1] left by rot positions, in place */
+local void rotate(unsigned char *list, unsigned len, unsigned rot)
+{
+    unsigned char tmp;
+    unsigned cycles;
+    unsigned char *start, *last, *to, *from;
+
+    /* normalize rot and handle degenerate cases */
+    if (len < 2) return;
+    if (rot >= len) rot %= len;
+    if (rot == 0) return;
+
+    /* pointer to last entry in list */
+    last = list + (len - 1);
+
+    /* do simple left shift by one */
+    if (rot == 1) {
+        tmp = *list;
+        memcpy(list, list + 1, len - 1);
+        *last = tmp;
+        return;
+    }
+
+    /* do simple right shift by one */
+    if (rot == len - 1) {
+        tmp = *last;
+        memmove(list + 1, list, len - 1);
+        *list = tmp;
+        return;
+    }
+
+    /* otherwise do rotate as a set of cycles in place */
+    cycles = gcd(len, rot);             /* number of cycles */
+    do {
+        start = from = list + cycles;   /* start index is arbitrary */
+        tmp = *from;                    /* save entry to be overwritten */
+        for (;;) {
+            to = from;                  /* next step in cycle */
+            from += rot;                /* go right rot positions */
+            if (from > last) from -= len;   /* (pointer better not wrap) */
+            if (from == start) break;   /* all but one shifted */
+            *to = *from;                /* shift left */
+        }
+        *to = tmp;                      /* complete the circle */
+    } while (--cycles);
+}
+
+/* structure for gzip file read operations */
+typedef struct {
+    int fd;                     /* file descriptor */
+    int size;                   /* 1 << size is bytes in buf */
+    unsigned left;              /* bytes available at next */
+    unsigned char *buf;         /* buffer */
+    unsigned char *next;        /* next byte in buffer */
+    char *name;                 /* file name for error messages */
+} file;
+
+/* reload buffer */
+local int readin(file *in)
+{
+    int len;
+
+    len = read(in->fd, in->buf, 1 << in->size);
+    if (len == -1) bye("error reading ", in->name);
+    in->left = (unsigned)len;
+    in->next = in->buf;
+    return len;
+}
+
+/* read from file in, exit if end-of-file */
+local int readmore(file *in)
+{
+    if (readin(in) == 0) bye("unexpected end of ", in->name);
+    return 0;
+}
+
+#define read1(in) (in->left == 0 ? readmore(in) : 0, \
+                   in->left--, *(in->next)++)
+
+/* skip over n bytes of in */
+local void skip(file *in, unsigned n)
+{
+    unsigned bypass;
+
+    if (n > in->left) {
+        n -= in->left;
+        bypass = n & ~((1U << in->size) - 1);
+        if (bypass) {
+            if (lseek(in->fd, (off_t)bypass, SEEK_CUR) == -1)
+                bye("seeking ", in->name);
+            n -= bypass;
+        }
+        readmore(in);
+        if (n > in->left)
+            bye("unexpected end of ", in->name);
+    }
+    in->left -= n;
+    in->next += n;
+}
+
+/* read a four-byte unsigned integer, little-endian, from in */
+unsigned long read4(file *in)
+{
+    unsigned long val;
+
+    val = read1(in);
+    val += (unsigned)read1(in) << 8;
+    val += (unsigned long)read1(in) << 16;
+    val += (unsigned long)read1(in) << 24;
+    return val;
+}
+
+/* skip over gzip header */
+local void gzheader(file *in)
+{
+    int flags;
+    unsigned n;
+
+    if (read1(in) != 31 || read1(in) != 139) bye(in->name, " not a gzip file");
+    if (read1(in) != 8) bye("unknown compression method in", in->name);
+    flags = read1(in);
+    if (flags & 0xe0) bye("unknown header flags set in", in->name);
+    skip(in, 6);
+    if (flags & 4) {
+        n = read1(in);
+        n += (unsigned)(read1(in)) << 8;
+        skip(in, n);
+    }
+    if (flags & 8) while (read1(in) != 0) ;
+    if (flags & 16) while (read1(in) != 0) ;
+    if (flags & 2) skip(in, 2);
+}
+
+/* decompress gzip file "name", return strm with a deflate stream ready to
+   continue compression of the data in the gzip file, and return a file
+   descriptor pointing to where to write the compressed data -- the deflate
+   stream is initialized to compress using level "level" */
+local int gzscan(char *name, z_stream *strm, int level)
+{
+    int ret, lastbit, left, full;
+    unsigned have;
+    unsigned long crc, tot;
+    unsigned char *window;
+    off_t lastoff, end;
+    file gz;
+
+    /* open gzip file */
+    gz.name = name;
+    gz.fd = open(name, O_RDWR, 0);
+    if (gz.fd == -1) bye("cannot open ", name);
+    gz.buf = malloc(CHUNK);
+    if (gz.buf == NULL) bye("out of memory", "");
+    gz.size = LGCHUNK;
+    gz.left = 0;
+
+    /* skip gzip header */
+    gzheader(&gz);
+
+    /* prepare to decompress */
+    window = malloc(DSIZE);
+    if (window == NULL) bye("out of memory", "");
+    strm->zalloc = Z_NULL;
+    strm->zfree = Z_NULL;
+    strm->opaque = Z_NULL;
+    ret = inflateInit2(strm, -15);
+    if (ret != Z_OK) bye("out of memory", " or library mismatch");
+
+    /* decompress the deflate stream, saving append information */
+    lastbit = 0;
+    lastoff = lseek(gz.fd, 0L, SEEK_CUR) - gz.left;
+    left = 0;
+    strm->avail_in = gz.left;
+    strm->next_in = gz.next;
+    crc = crc32(0L, Z_NULL, 0);
+    have = full = 0;
+    do {
+        /* if needed, get more input */
+        if (strm->avail_in == 0) {
+            readmore(&gz);
+            strm->avail_in = gz.left;
+            strm->next_in = gz.next;
+        }
+
+        /* set up output to next available section of sliding window */
+        strm->avail_out = DSIZE - have;
+        strm->next_out = window + have;
+
+        /* inflate and check for errors */
+        ret = inflate(strm, Z_BLOCK);
+        if (ret == Z_STREAM_ERROR) bye("internal stream error!", "");
+        if (ret == Z_MEM_ERROR) bye("out of memory", "");
+        if (ret == Z_DATA_ERROR)
+            bye("invalid compressed data--format violated in", name);
+
+        /* update crc and sliding window pointer */
+        crc = crc32(crc, window + have, DSIZE - have - strm->avail_out);
+        if (strm->avail_out)
+            have = DSIZE - strm->avail_out;
+        else {
+            have = 0;
+            full = 1;
+        }
+
+        /* process end of block */
+        if (strm->data_type & 128) {
+            if (strm->data_type & 64)
+                left = strm->data_type & 0x1f;
+            else {
+                lastbit = strm->data_type & 0x1f;
+                lastoff = lseek(gz.fd, 0L, SEEK_CUR) - strm->avail_in;
+            }
+        }
+    } while (ret != Z_STREAM_END);
+    inflateEnd(strm);
+    gz.left = strm->avail_in;
+    gz.next = strm->next_in;
+
+    /* save the location of the end of the compressed data */
+    end = lseek(gz.fd, 0L, SEEK_CUR) - gz.left;
+
+    /* check gzip trailer and save total for deflate */
+    if (crc != read4(&gz))
+        bye("invalid compressed data--crc mismatch in ", name);
+    tot = strm->total_out;
+    if ((tot & 0xffffffffUL) != read4(&gz))
+        bye("invalid compressed data--length mismatch in", name);
+
+    /* if not at end of file, warn */
+    if (gz.left || readin(&gz))
+        fprintf(stderr,
+            "gzappend warning: junk at end of gzip file overwritten\n");
+
+    /* clear last block bit */
+    lseek(gz.fd, lastoff - (lastbit != 0), SEEK_SET);
+    if (read(gz.fd, gz.buf, 1) != 1) bye("reading after seek on ", name);
+    *gz.buf = (unsigned char)(*gz.buf ^ (1 << ((8 - lastbit) & 7)));
+    lseek(gz.fd, -1L, SEEK_CUR);
+    if (write(gz.fd, gz.buf, 1) != 1) bye("writing after seek to ", name);
+
+    /* if window wrapped, build dictionary from window by rotating */
+    if (full) {
+        rotate(window, DSIZE, have);
+        have = DSIZE;
+    }
+
+    /* set up deflate stream with window, crc, total_in, and leftover bits */
+    ret = deflateInit2(strm, level, Z_DEFLATED, -15, 8, Z_DEFAULT_STRATEGY);
+    if (ret != Z_OK) bye("out of memory", "");
+    deflateSetDictionary(strm, window, have);
+    strm->adler = crc;
+    strm->total_in = tot;
+    if (left) {
+        lseek(gz.fd, --end, SEEK_SET);
+        if (read(gz.fd, gz.buf, 1) != 1) bye("reading after seek on ", name);
+        deflatePrime(strm, 8 - left, *gz.buf);
+    }
+    lseek(gz.fd, end, SEEK_SET);
+
+    /* clean up and return */
+    free(window);
+    free(gz.buf);
+    return gz.fd;
+}
+
+/* append file "name" to gzip file gd using deflate stream strm -- if last
+   is true, then finish off the deflate stream at the end */
+local void gztack(char *name, int gd, z_stream *strm, int last)
+{
+    int fd, len, ret;
+    unsigned left;
+    unsigned char *in, *out;
+
+    /* open file to compress and append */
+    fd = 0;
+    if (name != NULL) {
+        fd = open(name, O_RDONLY, 0);
+        if (fd == -1)
+            fprintf(stderr, "gzappend warning: %s not found, skipping ...\n",
+                    name);
+    }
+
+    /* allocate buffers */
+    in = fd == -1 ? NULL : malloc(CHUNK);
+    out = malloc(CHUNK);
+    if (out == NULL) bye("out of memory", "");
+
+    /* compress input file and append to gzip file */
+    do {
+        /* get more input */
+        len = fd == -1 ? 0 : read(fd, in, CHUNK);
+        if (len == -1) {
+            fprintf(stderr,
+                    "gzappend warning: error reading %s, skipping rest ...\n",
+                    name);
+            len = 0;
+        }
+        strm->avail_in = (unsigned)len;
+        strm->next_in = in;
+        if (len) strm->adler = crc32(strm->adler, in, (unsigned)len);
+
+        /* compress and write all available output */
+        do {
+            strm->avail_out = CHUNK;
+            strm->next_out = out;
+            ret = deflate(strm, last && len == 0 ? Z_FINISH : Z_NO_FLUSH);
+            left = CHUNK - strm->avail_out;
+            while (left) {
+                len = write(gd, out + CHUNK - strm->avail_out - left, left);
+                if (len == -1) bye("writing gzip file", "");
+                left -= (unsigned)len;
+            }
+        } while (strm->avail_out == 0 && ret != Z_STREAM_END);
+    } while (len != 0);
+
+    /* write trailer after last entry */
+    if (last) {
+        deflateEnd(strm);
+        out[0] = (unsigned char)(strm->adler);
+        out[1] = (unsigned char)(strm->adler >> 8);
+        out[2] = (unsigned char)(strm->adler >> 16);
+        out[3] = (unsigned char)(strm->adler >> 24);
+        out[4] = (unsigned char)(strm->total_in);
+        out[5] = (unsigned char)(strm->total_in >> 8);
+        out[6] = (unsigned char)(strm->total_in >> 16);
+        out[7] = (unsigned char)(strm->total_in >> 24);
+        len = 8;
+        do {
+            ret = write(gd, out + 8 - len, len);
+            if (ret == -1) bye("writing gzip file", "");
+            len -= ret;
+        } while (len);
+        close(gd);
+    }
+
+    /* clean up and return */
+    free(out);
+    if (in != NULL) free(in);
+    if (fd > 0) close(fd);
+}
+
+/* process the compression level option if present, scan the gzip file, and
+   append the specified files, or append the data from stdin if no other file
+   names are provided on the command line -- the gzip file must be writable
+   and seekable */
+int main(int argc, char **argv)
+{
+    int gd, level;
+    z_stream strm;
+
+    /* ignore command name */
+    argv++;
+
+    /* provide usage if no arguments */
+    if (*argv == NULL) {
+        printf("gzappend 1.1 (4 Nov 2003) Copyright (C) 2003 Mark Adler\n");
+        printf(
+            "usage: gzappend [-level] file.gz [ addthis [ andthis ... ]]\n");
+        return 0;
+    }
+
+    /* set compression level */
+    level = Z_DEFAULT_COMPRESSION;
+    if (argv[0][0] == '-') {
+        if (argv[0][1] < '0' || argv[0][1] > '9' || argv[0][2] != 0)
+            bye("invalid compression level", "");
+        level = argv[0][1] - '0';
+        if (*++argv == NULL) bye("no gzip file name after options", "");
+    }
+
+    /* prepare to append to gzip file */
+    gd = gzscan(*argv++, &strm, level);
+
+    /* append files on command line, or from stdin if none */
+    if (*argv == NULL)
+        gztack(NULL, gd, &strm, 1);
+    else
+        do {
+            gztack(*argv, gd, &strm, argv[1] == NULL);
+        } while (*++argv != NULL);
+    return 0;
+}
diff --git a/zlib/examples/gzjoin.c b/zlib/examples/gzjoin.c
new file mode 100644
index 0000000..129347c
--- /dev/null
+++ b/zlib/examples/gzjoin.c
@@ -0,0 +1,448 @@
+/* gzjoin -- command to join gzip files into one gzip file
+
+  Copyright (C) 2004 Mark Adler, all rights reserved
+  version 1.0, 11 Dec 2004
+
+  This software is provided 'as-is', without any express or implied
+  warranty.  In no event will the author be held liable for any damages
+  arising from the use of this software.
+
+  Permission is granted to anyone to use this software for any purpose,
+  including commercial applications, and to alter it and redistribute it
+  freely, subject to the following restrictions:
+
+  1. The origin of this software must not be misrepresented; you must not
+     claim that you wrote the original software. If you use this software
+     in a product, an acknowledgment in the product documentation would be
+     appreciated but is not required.
+  2. Altered source versions must be plainly marked as such, and must not be
+     misrepresented as being the original software.
+  3. This notice may not be removed or altered from any source distribution.
+
+  Mark Adler    madler@alumni.caltech.edu
+ */
+
+/*
+ * Change history:
+ *
+ * 1.0  11 Dec 2004     - First version
+ * 1.1  12 Jun 2005     - Changed ssize_t to long for portability
+ */
+
+/*
+   gzjoin takes one or more gzip files on the command line and writes out a
+   single gzip file that will uncompress to the concatenation of the
+   uncompressed data from the individual gzip files.  gzjoin does this without
+   having to recompress any of the data and without having to calculate a new
+   crc32 for the concatenated uncompressed data.  gzjoin does however have to
+   decompress all of the input data in order to find the bits in the compressed
+   data that need to be modified to concatenate the streams.
+
+   gzjoin does not do an integrity check on the input gzip files other than
+   checking the gzip header and decompressing the compressed data.  They are
+   otherwise assumed to be complete and correct.
+
+   Each joint between gzip files removes at least 18 bytes of previous trailer
+   and subsequent header, and inserts an average of about three bytes to the
+   compressed data in order to connect the streams.  The output gzip file
+   has a minimal ten-byte gzip header with no file name or modification time.
+
+   This program was written to illustrate the use of the Z_BLOCK option of
+   inflate() and the crc32_combine() function.  gzjoin will not compile with
+   versions of zlib earlier than 1.2.3.
+ */
+
+#include <stdio.h>      /* fputs(), fprintf(), fwrite(), putc() */
+#include <stdlib.h>     /* exit(), malloc(), free() */
+#include <fcntl.h>      /* open() */
+#include <unistd.h>     /* close(), read(), lseek() */
+#include "zlib.h"
+    /* crc32(), crc32_combine(), inflateInit2(), inflate(), inflateEnd() */
+
+#define local static
+
+/* exit with an error (return a value to allow use in an expression) */
+local int bail(char *why1, char *why2)
+{
+    fprintf(stderr, "gzjoin error: %s%s, output incomplete\n", why1, why2);
+    exit(1);
+    return 0;
+}
+
+/* -- simple buffered file input with access to the buffer -- */
+
+#define CHUNK 32768         /* must be a power of two and fit in unsigned */
+
+/* bin buffered input file type */
+typedef struct {
+    char *name;             /* name of file for error messages */
+    int fd;                 /* file descriptor */
+    unsigned left;          /* bytes remaining at next */
+    unsigned char *next;    /* next byte to read */
+    unsigned char *buf;     /* allocated buffer of length CHUNK */
+} bin;
+
+/* close a buffered file and free allocated memory */
+local void bclose(bin *in)
+{
+    if (in != NULL) {
+        if (in->fd != -1)
+            close(in->fd);
+        if (in->buf != NULL)
+            free(in->buf);
+        free(in);
+    }
+}
+
+/* open a buffered file for input, return a pointer to type bin, or NULL on
+   failure */
+local bin *bopen(char *name)
+{
+    bin *in;
+
+    in = malloc(sizeof(bin));
+    if (in == NULL)
+        return NULL;
+    in->buf = malloc(CHUNK);
+    in->fd = open(name, O_RDONLY, 0);
+    if (in->buf == NULL || in->fd == -1) {
+        bclose(in);
+        return NULL;
+    }
+    in->left = 0;
+    in->next = in->buf;
+    in->name = name;
+    return in;
+}
+
+/* load buffer from file, return -1 on read error, 0 or 1 on success, with
+   1 indicating that end-of-file was reached */
+local int bload(bin *in)
+{
+    long len;
+
+    if (in == NULL)
+        return -1;
+    if (in->left != 0)
+        return 0;
+    in->next = in->buf;
+    do {
+        len = (long)read(in->fd, in->buf + in->left, CHUNK - in->left);
+        if (len < 0)
+            return -1;
+        in->left += (unsigned)len;
+    } while (len != 0 && in->left < CHUNK);
+    return len == 0 ? 1 : 0;
+}
+
+/* get a byte from the file, bail if end of file */
+#define bget(in) (in->left ? 0 : bload(in), \
+                  in->left ? (in->left--, *(in->next)++) : \
+                    bail("unexpected end of file on ", in->name))
+
+/* get a four-byte little-endian unsigned integer from file */
+local unsigned long bget4(bin *in)
+{
+    unsigned long val;
+
+    val = bget(in);
+    val += (unsigned long)(bget(in)) << 8;
+    val += (unsigned long)(bget(in)) << 16;
+    val += (unsigned long)(bget(in)) << 24;
+    return val;
+}
+
+/* skip bytes in file */
+local void bskip(bin *in, unsigned skip)
+{
+    /* check pointer */
+    if (in == NULL)
+        return;
+
+    /* easy case -- skip bytes in buffer */
+    if (skip <= in->left) {
+        in->left -= skip;
+        in->next += skip;
+        return;
+    }
+
+    /* skip what's in buffer, discard buffer contents */
+    skip -= in->left;
+    in->left = 0;
+
+    /* seek past multiples of CHUNK bytes */
+    if (skip > CHUNK) {
+        unsigned left;
+
+        left = skip & (CHUNK - 1);
+        if (left == 0) {
+            /* exact number of chunks: seek all the way minus one byte to check
+               for end-of-file with a read */
+            lseek(in->fd, skip - 1, SEEK_CUR);
+            if (read(in->fd, in->buf, 1) != 1)
+                bail("unexpected end of file on ", in->name);
+            return;
+        }
+
+        /* skip the integral chunks, update skip with remainder */
+        lseek(in->fd, skip - left, SEEK_CUR);
+        skip = left;
+    }
+
+    /* read more input and skip remainder */
+    bload(in);
+    if (skip > in->left)
+        bail("unexpected end of file on ", in->name);
+    in->left -= skip;
+    in->next += skip;
+}
+
+/* -- end of buffered input functions -- */
+
+/* skip the gzip header from file in */
+local void gzhead(bin *in)
+{
+    int flags;
+
+    /* verify gzip magic header and compression method */
+    if (bget(in) != 0x1f || bget(in) != 0x8b || bget(in) != 8)
+        bail(in->name, " is not a valid gzip file");
+
+    /* get and verify flags */
+    flags = bget(in);
+    if ((flags & 0xe0) != 0)
+        bail("unknown reserved bits set in ", in->name);
+
+    /* skip modification time, extra flags, and os */
+    bskip(in, 6);
+
+    /* skip extra field if present */
+    if (flags & 4) {
+        unsigned len;
+
+        len = bget(in);
+        len += (unsigned)(bget(in)) << 8;
+        bskip(in, len);
+    }
+
+    /* skip file name if present */
+    if (flags & 8)
+        while (bget(in) != 0)
+            ;
+
+    /* skip comment if present */
+    if (flags & 16)
+        while (bget(in) != 0)
+            ;
+
+    /* skip header crc if present */
+    if (flags & 2)
+        bskip(in, 2);
+}
+
+/* write a four-byte little-endian unsigned integer to out */
+local void put4(unsigned long val, FILE *out)
+{
+    putc(val & 0xff, out);
+    putc((val >> 8) & 0xff, out);
+    putc((val >> 16) & 0xff, out);
+    putc((val >> 24) & 0xff, out);
+}
+
+/* Load up zlib stream from buffered input, bail if end of file */
+local void zpull(z_streamp strm, bin *in)
+{
+    if (in->left == 0)
+        bload(in);
+    if (in->left == 0)
+        bail("unexpected end of file on ", in->name);
+    strm->avail_in = in->left;
+    strm->next_in = in->next;
+}
+
+/* Write header for gzip file to out and initialize trailer. */
+local void gzinit(unsigned long *crc, unsigned long *tot, FILE *out)
+{
+    fwrite("\x1f\x8b\x08\0\0\0\0\0\0\xff", 1, 10, out);
+    *crc = crc32(0L, Z_NULL, 0);
+    *tot = 0;
+}
+
+/* Copy the compressed data from name, zeroing the last block bit of the last
+   block if clr is true, and adding empty blocks as needed to get to a byte
+   boundary.  If clr is false, then the last block becomes the last block of
+   the output, and the gzip trailer is written.  crc and tot maintains the
+   crc and length (modulo 2^32) of the output for the trailer.  The resulting
+   gzip file is written to out.  gzinit() must be called before the first call
+   of gzcopy() to write the gzip header and to initialize crc and tot. */
+local void gzcopy(char *name, int clr, unsigned long *crc, unsigned long *tot,
+                  FILE *out)
+{
+    int ret;                /* return value from zlib functions */
+    int pos;                /* where the "last block" bit is in byte */
+    int last;               /* true if processing the last block */
+    bin *in;                /* buffered input file */
+    unsigned char *start;   /* start of compressed data in buffer */
+    unsigned char *junk;    /* buffer for uncompressed data -- discarded */
+    z_off_t len;            /* length of uncompressed data (support > 4 GB) */
+    z_stream strm;          /* zlib inflate stream */
+
+    /* open gzip file and skip header */
+    in = bopen(name);
+    if (in == NULL)
+        bail("could not open ", name);
+    gzhead(in);
+
+    /* allocate buffer for uncompressed data and initialize raw inflate
+       stream */
+    junk = malloc(CHUNK);
+    strm.zalloc = Z_NULL;
+    strm.zfree = Z_NULL;
+    strm.opaque = Z_NULL;
+    strm.avail_in = 0;
+    strm.next_in = Z_NULL;
+    ret = inflateInit2(&strm, -15);
+    if (junk == NULL || ret != Z_OK)
+        bail("out of memory", "");
+
+    /* inflate and copy compressed data, clear last-block bit if requested */
+    len = 0;
+    zpull(&strm, in);
+    start = strm.next_in;
+    last = start[0] & 1;
+    if (last && clr)
+        start[0] &= ~1;
+    strm.avail_out = 0;
+    for (;;) {
+        /* if input used and output done, write used input and get more */
+        if (strm.avail_in == 0 && strm.avail_out != 0) {
+            fwrite(start, 1, strm.next_in - start, out);
+            start = in->buf;
+            in->left = 0;
+            zpull(&strm, in);
+        }
+
+        /* decompress -- return early when end-of-block reached */
+        strm.avail_out = CHUNK;
+        strm.next_out = junk;
+        ret = inflate(&strm, Z_BLOCK);
+        switch (ret) {
+        case Z_MEM_ERROR:
+            bail("out of memory", "");
+        case Z_DATA_ERROR:
+            bail("invalid compressed data in ", in->name);
+        }
+
+        /* update length of uncompressed data */
+        len += CHUNK - strm.avail_out;
+
+        /* check for block boundary (only get this when block copied out) */
+        if (strm.data_type & 128) {
+            /* if that was the last block, then done */
+            if (last)
+                break;
+
+            /* number of unused bits in last byte */
+            pos = strm.data_type & 7;
+
+            /* find the next last-block bit */
+            if (pos != 0) {
+                /* next last-block bit is in last used byte */
+                pos = 0x100 >> pos;
+                last = strm.next_in[-1] & pos;
+                if (last && clr)
+                    strm.next_in[-1] &= ~pos;
+            }
+            else {
+                /* next last-block bit is in next unused byte */
+                if (strm.avail_in == 0) {
+                    /* don't have that byte yet -- get it */
+                    fwrite(start, 1, strm.next_in - start, out);
+                    start = in->buf;
+                    in->left = 0;
+                    zpull(&strm, in);
+                }
+                last = strm.next_in[0] & 1;
+                if (last && clr)
+                    strm.next_in[0] &= ~1;
+            }
+        }
+    }
+
+    /* update buffer with unused input */
+    in->left = strm.avail_in;
+    in->next = strm.next_in;
+
+    /* copy used input, write empty blocks to get to byte boundary */
+    pos = strm.data_type & 7;
+    fwrite(start, 1, in->next - start - 1, out);
+    last = in->next[-1];
+    if (pos == 0 || !clr)
+        /* already at byte boundary, or last file: write last byte */
+        putc(last, out);
+    else {
+        /* append empty blocks to last byte */
+        last &= ((0x100 >> pos) - 1);       /* assure unused bits are zero */
+        if (pos & 1) {
+            /* odd -- append an empty stored block */
+            putc(last, out);
+            if (pos == 1)
+                putc(0, out);               /* two more bits in block header */
+            fwrite("\0\0\xff\xff", 1, 4, out);
+        }
+        else {
+            /* even -- append 1, 2, or 3 empty fixed blocks */
+            switch (pos) {
+            case 6:
+                putc(last | 8, out);
+                last = 0;
+            case 4:
+                putc(last | 0x20, out);
+                last = 0;
+            case 2:
+                putc(last | 0x80, out);
+                putc(0, out);
+            }
+        }
+    }
+
+    /* update crc and tot */
+    *crc = crc32_combine(*crc, bget4(in), len);
+    *tot += (unsigned long)len;
+
+    /* clean up */
+    inflateEnd(&strm);
+    free(junk);
+    bclose(in);
+
+    /* write trailer if this is the last gzip file */
+    if (!clr) {
+        put4(*crc, out);
+        put4(*tot, out);
+    }
+}
+
+/* join the gzip files on the command line, write result to stdout */
+int main(int argc, char **argv)
+{
+    unsigned long crc, tot;     /* running crc and total uncompressed length */
+
+    /* skip command name */
+    argc--;
+    argv++;
+
+    /* show usage if no arguments */
+    if (argc == 0) {
+        fputs("gzjoin usage: gzjoin f1.gz [f2.gz [f3.gz ...]] > fjoin.gz\n",
+              stderr);
+        return 0;
+    }
+
+    /* join gzip files on command line and write to stdout */
+    gzinit(&crc, &tot, stdout);
+    while (argc--)
+        gzcopy(*argv++, argc, &crc, &tot, stdout);
+
+    /* done */
+    return 0;
+}
diff --git a/zlib/examples/gzlog.c b/zlib/examples/gzlog.c
new file mode 100644
index 0000000..d70aaca
--- /dev/null
+++ b/zlib/examples/gzlog.c
@@ -0,0 +1,1058 @@
+/*
+ * gzlog.c
+ * Copyright (C) 2004, 2008 Mark Adler, all rights reserved
+ * For conditions of distribution and use, see copyright notice in gzlog.h
+ * version 2.0, 25 Apr 2008
+ */
+
+/*
+   gzlog provides a mechanism for frequently appending short strings to a gzip
+   file that is efficient both in execution time and compression ratio.  The
+   strategy is to write the short strings in an uncompressed form to the end of
+   the gzip file, only compressing when the amount of uncompressed data has
+   reached a given threshold.
+
+   gzlog also provides protection against interruptions in the process due to
+   system crashes.  The status of the operation is recorded in an extra field
+   in the gzip file, and is only updated once the gzip file is brought to a
+   valid state.  The last data to be appended or compressed is saved in an
+   auxiliary file, so that if the operation is interrupted, it can be completed
+   the next time an append operation is attempted.
+
+   gzlog maintains another auxiliary file with the last 32K of data from the
+   compressed portion, which is preloaded for the compression of the subsequent
+   data.  This minimizes the impact to the compression ratio of appending.
+ */
+
+/*
+   Operations Concept:
+
+   Files (log name "foo"):
+   foo.gz -- gzip file with the complete log
+   foo.add -- last message to append or last data to compress
+   foo.dict -- dictionary of the last 32K of data for next compression
+   foo.temp -- temporary dictionary file for compression after this one
+   foo.lock -- lock file for reading and writing the other files
+   foo.repairs -- log file for log file recovery operations (not compressed)
+
+   gzip file structure:
+   - fixed-length (no file name) header with extra field (see below)
+   - compressed data ending initially with empty stored block
+   - uncompressed data filling out originally empty stored block and
+     subsequent stored blocks as needed (16K max each)
+   - gzip trailer
+   - no junk at end (no other gzip streams)
+
+   When appending data, the information in the first three items above plus the
+   foo.add file are sufficient to recover an interrupted append operation.  The
+   extra field has the necessary information to restore the start of the last
+   stored block and determine where to append the data in the foo.add file, as
+   well as the crc and length of the gzip data before the append operation.
+
+   The foo.add file is created before the gzip file is marked for append, and
+   deleted after the gzip file is marked as complete.  So if the append
+   operation is interrupted, the data to add will still be there.  If due to
+   some external force, the foo.add file gets deleted between when the append
+   operation was interrupted and when recovery is attempted, the gzip file will
+   still be restored, but without the appended data.
+
+   When compressing data, the information in the first two items above plus the
+   foo.add file are sufficient to recover an interrupted compress operation.
+   The extra field has the necessary information to find the end of the
+   compressed data, and contains both the crc and length of just the compressed
+   data and of the complete set of data including the contents of the foo.add
+   file.
+
+   Again, the foo.add file is maintained during the compress operation in case
+   of an interruption.  If in the unlikely event the foo.add file with the data
+   to be compressed is missing due to some external force, a gzip file with
+   just the previous compressed data will be reconstructed.  In this case, all
+   of the data that was to be compressed is lost (approximately one megabyte).
+   This will not occur if all that happened was an interruption of the compress
+   operation.
+
+   The third state that is marked is the replacement of the old dictionary with
+   the new dictionary after a compress operation.  Once compression is
+   complete, the gzip file is marked as being in the replace state.  This
+   completes the gzip file, so an interrupt after being so marked does not
+   result in recompression.  Then the dictionary file is replaced, and the gzip
+   file is marked as completed.  This state prevents the possibility of
+   restarting compression with the wrong dictionary file.
+
+   All three operations are wrapped by a lock/unlock procedure.  In order to
+   gain exclusive access to the log files, first a foo.lock file must be
+   exclusively created.  When all operations are complete, the lock is
+   released by deleting the foo.lock file.  If when attempting to create the
+   lock file, it already exists and the modify time of the lock file is more
+   than five minutes old (set by the PATIENCE define below), then the old
+   lock file is considered stale and deleted, and the exclusive creation of
+   the lock file is retried.  To assure that there are no false assessments
+   of the staleness of the lock file, the operations periodically touch the
+   lock file to update the modified date.
+
+   Following is the definition of the extra field with all of the information
+   required to enable the above append and compress operations and their
+   recovery if interrupted.  Multi-byte values are stored little endian
+   (consistent with the gzip format).  File pointers are eight bytes long.
+   The crc's and lengths for the gzip trailer are four bytes long.  (Note that
+   the length at the end of a gzip file is used for error checking only, and
+   for large files is actually the length modulo 2^32.)  The stored block
+   length is two bytes long.  The gzip extra field two-byte identification is
+   "ap" for append.  It is assumed that writing the extra field to the file is
+   an "atomic" operation.  That is, either all of the extra field is written
+   to the file, or none of it is, if the operation is interrupted right at the
+   point of updating the extra field.  This is a reasonable assumption, since
+   the extra field is within the first 52 bytes of the file, which is smaller
+   than any expected block size for a mass storage device (usually 512 bytes or
+   larger).
+
+   Extra field (35 bytes):
+   - Pointer to first stored block length -- this points to the two-byte length
+     of the first stored block, which is followed by the two-byte, one's
+     complement of that length.  The stored block length is preceded by the
+     three-bit header of the stored block, which is the actual start of the
+     stored block in the deflate format.  See the bit offset field below.
+   - Pointer to the last stored block length.  This is the same as above, but
+     for the last stored block of the uncompressed data in the gzip file.
+     Initially this is the same as the first stored block length pointer.
+     When the stored block gets to 16K (see the MAX_STORE define), then a new
+     stored block as added, at which point the last stored block length pointer
+     is different from the first stored block length pointer.  When they are
+     different, the first bit of the last stored block header is eight bits, or
+     one byte back from the block length.
+   - Compressed data crc and length.  This is the crc and length of the data
+     that is in the compressed portion of the deflate stream.  These are used
+     only in the event that the foo.add file containing the data to compress is
+     lost after a compress operation is interrupted.
+   - Total data crc and length.  This is the crc and length of all of the data
+     stored in the gzip file, compressed and uncompressed.  It is used to
+     reconstruct the gzip trailer when compressing, as well as when recovering
+     interrupted operations.
+   - Final stored block length.  This is used to quickly find where to append,
+     and allows the restoration of the original final stored block state when
+     an append operation is interrupted.
+   - First stored block start as the number of bits back from the final stored
+     block first length byte.  This value is in the range of 3..10, and is
+     stored as the low three bits of the final byte of the extra field after
+     subtracting three (0..7).  This allows the last-block bit of the stored
+     block header to be updated when a new stored block is added, for the case
+     when the first stored block and the last stored block are the same.  (When
+     they are different, the numbers of bits back is known to be eight.)  This
+     also allows for new compressed data to be appended to the old compressed
+     data in the compress operation, overwriting the previous first stored
+     block, or for the compressed data to be terminated and a valid gzip file
+     reconstructed on the off chance that a compression operation was
+     interrupted and the data to compress in the foo.add file was deleted.
+   - The operation in process.  This is the next two bits in the last byte (the
+     bits under the mask 0x18).  The are interpreted as 0: nothing in process,
+     1: append in process, 2: compress in process, 3: replace in process.
+   - The top three bits of the last byte in the extra field are reserved and
+     are currently set to zero.
+
+   Main procedure:
+   - Exclusively create the foo.lock file using the O_CREAT and O_EXCL modes of
+     the system open() call.  If the modify time of an existing lock file is
+     more than PATIENCE seconds old, then the lock file is deleted and the
+     exclusive create is retried.
+   - Load the extra field from the foo.gz file, and see if an operation was in
+     progress but not completed.  If so, apply the recovery procedure below.
+   - Perform the append procedure with the provided data.
+   - If the uncompressed data in the foo.gz file is 1MB or more, apply the
+     compress procedure.
+   - Delete the foo.lock file.
+
+   Append procedure:
+   - Put what to append in the foo.add file so that the operation can be
+     restarted if this procedure is interrupted.
+   - Mark the foo.gz extra field with the append operation in progress.
+   + Restore the original last-block bit and stored block length of the last
+     stored block from the information in the extra field, in case a previous
+     append operation was interrupted.
+   - Append the provided data to the last stored block, creating new stored
+     blocks as needed and updating the stored blocks last-block bits and
+     lengths.
+   - Update the crc and length with the new data, and write the gzip trailer.
+   - Write over the extra field (with a single write operation) with the new
+     pointers, lengths, and crc's, and mark the gzip file as not in process.
+     Though there is still a foo.add file, it will be ignored since nothing
+     is in process.  If a foo.add file is leftover from a previously
+     completed operation, it is truncated when writing new data to it.
+   - Delete the foo.add file.
+
+   Compress and replace procedures:
+   - Read all of the uncompressed data in the stored blocks in foo.gz and write
+     it to foo.add.  Also write foo.temp with the last 32K of that data to
+     provide a dictionary for the next invocation of this procedure.
+   - Rewrite the extra field marking foo.gz with a compression in process.
+   * If there is no data provided to compress (due to a missing foo.add file
+     when recovering), reconstruct and truncate the foo.gz file to contain
+     only the previous compressed data and proceed to the step after the next
+     one.  Otherwise ...
+   - Compress the data with the dictionary in foo.dict, and write to the
+     foo.gz file starting at the bit immediately following the last previously
+     compressed block.  If there is no foo.dict, proceed anyway with the
+     compression at slightly reduced efficiency.  (For the foo.dict file to be
+     missing requires some external failure beyond simply the interruption of
+     a compress operation.)  During this process, the foo.lock file is
+     periodically touched to assure that that file is not considered stale by
+     another process before we're done.  The deflation is terminated with a
+     non-last empty static block (10 bits long), that is then located and
+     written over by a last-bit-set empty stored block.
+   - Append the crc and length of the data in the gzip file (previously
+     calculated during the append operations).
+   - Write over the extra field with the updated stored block offsets, bits
+     back, crc's, and lengths, and mark foo.gz as in process for a replacement
+     of the dictionary.
+   @ Delete the foo.add file.
+   - Replace foo.dict with foo.temp.
+   - Write over the extra field, marking foo.gz as complete.
+
+   Recovery procedure:
+   - If not a replace recovery, read in the foo.add file, and provide that data
+     to the appropriate recovery below.  If there is no foo.add file, provide
+     a zero data length to the recovery.  In that case, the append recovery
+     restores the foo.gz to the previous compressed + uncompressed data state.
+     For the the compress recovery, a missing foo.add file results in foo.gz
+     being restored to the previous compressed-only data state.
+   - Append recovery:
+     - Pick up append at + step above
+   - Compress recovery:
+     - Pick up compress at * step above
+   - Replace recovery:
+     - Pick up compress at @ step above
+   - Log the repair with a date stamp in foo.repairs
+ */
+
+#include <sys/types.h>
+#include <stdio.h>      /* rename, fopen, fprintf, fclose */
+#include <stdlib.h>     /* malloc, free */
+#include <string.h>     /* strlen, strrchr, strcpy, strncpy, strcmp */
+#include <fcntl.h>      /* open */
+#include <unistd.h>     /* lseek, read, write, close, unlink, sleep, */
+                        /* ftruncate, fsync */
+#include <errno.h>      /* errno */
+#include <time.h>       /* time, ctime */
+#include <sys/stat.h>   /* stat */
+#include <sys/time.h>   /* utimes */
+#include "zlib.h"       /* crc32 */
+
+#include "gzlog.h"      /* header for external access */
+
+#define local static
+typedef unsigned int uint;
+typedef unsigned long ulong;
+
+/* Macro for debugging to deterministically force recovery operations */
+#ifdef DEBUG
+    #include <setjmp.h>         /* longjmp */
+    jmp_buf gzlog_jump;         /* where to go back to */
+    int gzlog_bail = 0;         /* which point to bail at (1..8) */
+    int gzlog_count = -1;       /* number of times through to wait */
+#   define BAIL(n) do { if (n == gzlog_bail && gzlog_count-- == 0) \
+                            longjmp(gzlog_jump, gzlog_bail); } while (0)
+#else
+#   define BAIL(n)
+#endif
+
+/* how old the lock file can be in seconds before considering it stale */
+#define PATIENCE 300
+
+/* maximum stored block size in Kbytes -- must be in 1..63 */
+#define MAX_STORE 16
+
+/* number of stored Kbytes to trigger compression (must be >= 32 to allow
+   dictionary construction, and <= 204 * MAX_STORE, in order for >> 10 to
+   discard the stored block headers contribution of five bytes each) */
+#define TRIGGER 1024
+
+/* size of a deflate dictionary (this cannot be changed) */
+#define DICT 32768U
+
+/* values for the operation (2 bits) */
+#define NO_OP 0
+#define APPEND_OP 1
+#define COMPRESS_OP 2
+#define REPLACE_OP 3
+
+/* macros to extract little-endian integers from an unsigned byte buffer */
+#define PULL2(p) ((p)[0]+((uint)((p)[1])<<8))
+#define PULL4(p) (PULL2(p)+((ulong)PULL2(p+2)<<16))
+#define PULL8(p) (PULL4(p)+((off_t)PULL4(p+4)<<32))
+
+/* macros to store integers into a byte buffer in little-endian order */
+#define PUT2(p,a) do {(p)[0]=a;(p)[1]=(a)>>8;} while(0)
+#define PUT4(p,a) do {PUT2(p,a);PUT2(p+2,a>>16);} while(0)
+#define PUT8(p,a) do {PUT4(p,a);PUT4(p+4,a>>32);} while(0)
+
+/* internal structure for log information */
+#define LOGID "\106\035\172"    /* should be three non-zero characters */
+struct log {
+    char id[4];     /* contains LOGID to detect inadvertent overwrites */
+    int fd;         /* file descriptor for .gz file, opened read/write */
+    char *path;     /* allocated path, e.g. "/var/log/foo" or "foo" */
+    char *end;      /* end of path, for appending suffices such as ".gz" */
+    off_t first;    /* offset of first stored block first length byte */
+    int back;       /* location of first block id in bits back from first */
+    uint stored;    /* bytes currently in last stored block */
+    off_t last;     /* offset of last stored block first length byte */
+    ulong ccrc;     /* crc of compressed data */
+    ulong clen;     /* length (modulo 2^32) of compressed data */
+    ulong tcrc;     /* crc of total data */
+    ulong tlen;     /* length (modulo 2^32) of total data */
+    time_t lock;    /* last modify time of our lock file */
+};
+
+/* gzip header for gzlog */
+local unsigned char log_gzhead[] = {
+    0x1f, 0x8b,                 /* magic gzip id */
+    8,                          /* compression method is deflate */
+    4,                          /* there is an extra field (no file name) */
+    0, 0, 0, 0,                 /* no modification time provided */
+    0, 0xff,                    /* no extra flags, no OS specified */
+    39, 0, 'a', 'p', 35, 0      /* extra field with "ap" subfield */
+                                /* 35 is EXTRA, 39 is EXTRA + 4 */
+};
+
+#define HEAD sizeof(log_gzhead)     /* should be 16 */
+
+/* initial gzip extra field content (52 == HEAD + EXTRA + 1) */
+local unsigned char log_gzext[] = {
+    52, 0, 0, 0, 0, 0, 0, 0,    /* offset of first stored block length */
+    52, 0, 0, 0, 0, 0, 0, 0,    /* offset of last stored block length */
+    0, 0, 0, 0, 0, 0, 0, 0,     /* compressed data crc and length */
+    0, 0, 0, 0, 0, 0, 0, 0,     /* total data crc and length */
+    0, 0,                       /* final stored block data length */
+    5                           /* op is NO_OP, last bit 8 bits back */
+};
+
+#define EXTRA sizeof(log_gzext)     /* should be 35 */
+
+/* initial gzip data and trailer */
+local unsigned char log_gzbody[] = {
+    1, 0, 0, 0xff, 0xff,        /* empty stored block (last) */
+    0, 0, 0, 0,                 /* crc */
+    0, 0, 0, 0                  /* uncompressed length */
+};
+
+#define BODY sizeof(log_gzbody)
+
+/* Exclusively create foo.lock in order to negotiate exclusive access to the
+   foo.* files.  If the modify time of an existing lock file is greater than
+   PATIENCE seconds in the past, then consider the lock file to have been
+   abandoned, delete it, and try the exclusive create again.  Save the lock
+   file modify time for verification of ownership.  Return 0 on success, or -1
+   on failure, usually due to an access restriction or invalid path.  Note that
+   if stat() or unlink() fails, it may be due to another process noticing the
+   abandoned lock file a smidge sooner and deleting it, so those are not
+   flagged as an error. */
+local int log_lock(struct log *log)
+{
+    int fd;
+    struct stat st;
+
+    strcpy(log->end, ".lock");
+    while ((fd = open(log->path, O_CREAT | O_EXCL, 0644)) < 0) {
+        if (errno != EEXIST)
+            return -1;
+        if (stat(log->path, &st) == 0 && time(NULL) - st.st_mtime > PATIENCE) {
+            unlink(log->path);
+            continue;
+        }
+        sleep(2);       /* relinquish the CPU for two seconds while waiting */
+    }
+    close(fd);
+    if (stat(log->path, &st) == 0)
+        log->lock = st.st_mtime;
+    return 0;
+}
+
+/* Update the modify time of the lock file to now, in order to prevent another
+   task from thinking that the lock is stale.  Save the lock file modify time
+   for verification of ownership. */
+local void log_touch(struct log *log)
+{
+    struct stat st;
+
+    strcpy(log->end, ".lock");
+    utimes(log->path, NULL);
+    if (stat(log->path, &st) == 0)
+        log->lock = st.st_mtime;
+}
+
+/* Check the log file modify time against what is expected.  Return true if
+   this is not our lock.  If it is our lock, touch it to keep it. */
+local int log_check(struct log *log)
+{
+    struct stat st;
+
+    strcpy(log->end, ".lock");
+    if (stat(log->path, &st) || st.st_mtime != log->lock)
+        return 1;
+    log_touch(log);
+    return 0;
+}
+
+/* Unlock a previously acquired lock, but only if it's ours. */
+local void log_unlock(struct log *log)
+{
+    if (log_check(log))
+        return;
+    strcpy(log->end, ".lock");
+    unlink(log->path);
+    log->lock = 0;
+}
+
+/* Check the gzip header and read in the extra field, filling in the values in
+   the log structure.  Return op on success or -1 if the gzip header was not as
+   expected.  op is the current operation in progress last written to the extra
+   field.  This assumes that the gzip file has already been opened, with the
+   file descriptor log->fd. */
+local int log_head(struct log *log)
+{
+    int op;
+    unsigned char buf[HEAD + EXTRA];
+
+    if (lseek(log->fd, 0, SEEK_SET) < 0 ||
+        read(log->fd, buf, HEAD + EXTRA) != HEAD + EXTRA ||
+        memcmp(buf, log_gzhead, HEAD)) {
+        return -1;
+    }
+    log->first = PULL8(buf + HEAD);
+    log->last = PULL8(buf + HEAD + 8);
+    log->ccrc = PULL4(buf + HEAD + 16);
+    log->clen = PULL4(buf + HEAD + 20);
+    log->tcrc = PULL4(buf + HEAD + 24);
+    log->tlen = PULL4(buf + HEAD + 28);
+    log->stored = PULL2(buf + HEAD + 32);
+    log->back = 3 + (buf[HEAD + 34] & 7);
+    op = (buf[HEAD + 34] >> 3) & 3;
+    return op;
+}
+
+/* Write over the extra field contents, marking the operation as op.  Use fsync
+   to assure that the device is written to, and in the requested order.  This
+   operation, and only this operation, is assumed to be atomic in order to
+   assure that the log is recoverable in the event of an interruption at any
+   point in the process.  Return -1 if the write to foo.gz failed. */
+local int log_mark(struct log *log, int op)
+{
+    int ret;
+    unsigned char ext[EXTRA];
+
+    PUT8(ext, log->first);
+    PUT8(ext + 8, log->last);
+    PUT4(ext + 16, log->ccrc);
+    PUT4(ext + 20, log->clen);
+    PUT4(ext + 24, log->tcrc);
+    PUT4(ext + 28, log->tlen);
+    PUT2(ext + 32, log->stored);
+    ext[34] = log->back - 3 + (op << 3);
+    fsync(log->fd);
+    ret = lseek(log->fd, HEAD, SEEK_SET) < 0 ||
+          write(log->fd, ext, EXTRA) != EXTRA ? -1 : 0;
+    fsync(log->fd);
+    return ret;
+}
+
+/* Rewrite the last block header bits and subsequent zero bits to get to a byte
+   boundary, setting the last block bit if last is true, and then write the
+   remainder of the stored block header (length and one's complement).  Leave
+   the file pointer after the end of the last stored block data.  Return -1 if
+   there is a read or write failure on the foo.gz file */
+local int log_last(struct log *log, int last)
+{
+    int back, len, mask;
+    unsigned char buf[6];
+
+    /* determine the locations of the bytes and bits to modify */
+    back = log->last == log->first ? log->back : 8;
+    len = back > 8 ? 2 : 1;                 /* bytes back from log->last */
+    mask = 0x80 >> ((back - 1) & 7);        /* mask for block last-bit */
+
+    /* get the byte to modify (one or two back) into buf[0] -- don't need to
+       read the byte if the last-bit is eight bits back, since in that case
+       the entire byte will be modified */
+    buf[0] = 0;
+    if (back != 8 && (lseek(log->fd, log->last - len, SEEK_SET) < 0 ||
+                      read(log->fd, buf, 1) != 1))
+        return -1;
+
+    /* change the last-bit of the last stored block as requested -- note
+       that all bits above the last-bit are set to zero, per the type bits
+       of a stored block being 00 and per the convention that the bits to
+       bring the stream to a byte boundary are also zeros */
+    buf[1] = 0;
+    buf[2 - len] = (*buf & (mask - 1)) + (last ? mask : 0);
+
+    /* write the modified stored block header and lengths, move the file
+       pointer to after the last stored block data */
+    PUT2(buf + 2, log->stored);
+    PUT2(buf + 4, log->stored ^ 0xffff);
+    return lseek(log->fd, log->last - len, SEEK_SET) < 0 ||
+           write(log->fd, buf + 2 - len, len + 4) != len + 4 ||
+           lseek(log->fd, log->stored, SEEK_CUR) < 0 ? -1 : 0;
+}
+
+/* Append len bytes from data to the locked and open log file.  len may be zero
+   if recovering and no .add file was found.  In that case, the previous state
+   of the foo.gz file is restored.  The data is appended uncompressed in
+   deflate stored blocks.  Return -1 if there was an error reading or writing
+   the foo.gz file. */
+local int log_append(struct log *log, unsigned char *data, size_t len)
+{
+    uint put;
+    off_t end;
+    unsigned char buf[8];
+
+    /* set the last block last-bit and length, in case recovering an
+       interrupted append, then position the file pointer to append to the
+       block */
+    if (log_last(log, 1))
+        return -1;
+
+    /* append, adding stored blocks and updating the offset of the last stored
+       block as needed, and update the total crc and length */
+    while (len) {
+        /* append as much as we can to the last block */
+        put = (MAX_STORE << 10) - log->stored;
+        if (put > len)
+            put = (uint)len;
+        if (put) {
+            if (write(log->fd, data, put) != put)
+                return -1;
+            BAIL(1);
+            log->tcrc = crc32(log->tcrc, data, put);
+            log->tlen += put;
+            log->stored += put;
+            data += put;
+            len -= put;
+        }
+
+        /* if we need to, add a new empty stored block */
+        if (len) {
+            /* mark current block as not last */
+            if (log_last(log, 0))
+                return -1;
+
+            /* point to new, empty stored block */
+            log->last += 4 + log->stored + 1;
+            log->stored = 0;
+        }
+
+        /* mark last block as last, update its length */
+        if (log_last(log, 1))
+            return -1;
+        BAIL(2);
+    }
+
+    /* write the new crc and length trailer, and truncate just in case (could
+       be recovering from partial append with a missing foo.add file) */
+    PUT4(buf, log->tcrc);
+    PUT4(buf + 4, log->tlen);
+    if (write(log->fd, buf, 8) != 8 ||
+        (end = lseek(log->fd, 0, SEEK_CUR)) < 0 || ftruncate(log->fd, end))
+        return -1;
+
+    /* write the extra field, marking the log file as done, delete .add file */
+    if (log_mark(log, NO_OP))
+        return -1;
+    strcpy(log->end, ".add");
+    unlink(log->path);          /* ignore error, since may not exist */
+    return 0;
+}
+
+/* Replace the foo.dict file with the foo.temp file.  Also delete the foo.add
+   file, since the compress operation may have been interrupted before that was
+   done.  Returns 1 if memory could not be allocated, or -1 if reading or
+   writing foo.gz fails, or if the rename fails for some reason other than
+   foo.temp not existing.  foo.temp not existing is a permitted error, since
+   the replace operation may have been interrupted after the rename is done,
+   but before foo.gz is marked as complete. */
+local int log_replace(struct log *log)
+{
+    int ret;
+    char *dest;
+
+    /* delete foo.add file */
+    strcpy(log->end, ".add");
+    unlink(log->path);         /* ignore error, since may not exist */
+    BAIL(3);
+
+    /* rename foo.name to foo.dict, replacing foo.dict if it exists */
+    strcpy(log->end, ".dict");
+    dest = malloc(strlen(log->path) + 1);
+    if (dest == NULL)
+        return -2;
+    strcpy(dest, log->path);
+    strcpy(log->end, ".temp");
+    ret = rename(log->path, dest);
+    free(dest);
+    if (ret && errno != ENOENT)
+        return -1;
+    BAIL(4);
+
+    /* mark the foo.gz file as done */
+    return log_mark(log, NO_OP);
+}
+
+/* Compress the len bytes at data and append the compressed data to the
+   foo.gz deflate data immediately after the previous compressed data.  This
+   overwrites the previous uncompressed data, which was stored in foo.add
+   and is the data provided in data[0..len-1].  If this operation is
+   interrupted, it picks up at the start of this routine, with the foo.add
+   file read in again.  If there is no data to compress (len == 0), then we
+   simply terminate the foo.gz file after the previously compressed data,
+   appending a final empty stored block and the gzip trailer.  Return -1 if
+   reading or writing the log.gz file failed, or -2 if there was a memory
+   allocation failure. */
+local int log_compress(struct log *log, unsigned char *data, size_t len)
+{
+    int fd;
+    uint got, max;
+    ssize_t dict;
+    off_t end;
+    z_stream strm;
+    unsigned char buf[DICT];
+
+    /* compress and append compressed data */
+    if (len) {
+        /* set up for deflate, allocating memory */
+        strm.zalloc = Z_NULL;
+        strm.zfree = Z_NULL;
+        strm.opaque = Z_NULL;
+        if (deflateInit2(&strm, Z_DEFAULT_COMPRESSION, Z_DEFLATED, -15, 8,
+                         Z_DEFAULT_STRATEGY) != Z_OK)
+            return -2;
+
+        /* read in dictionary (last 32K of data that was compressed) */
+        strcpy(log->end, ".dict");
+        fd = open(log->path, O_RDONLY, 0);
+        if (fd >= 0) {
+            dict = read(fd, buf, DICT);
+            close(fd);
+            if (dict < 0) {
+                deflateEnd(&strm);
+                return -1;
+            }
+            if (dict)
+                deflateSetDictionary(&strm, buf, (uint)dict);
+        }
+        log_touch(log);
+
+        /* prime deflate with last bits of previous block, position write
+           pointer to write those bits and overwrite what follows */
+        if (lseek(log->fd, log->first - (log->back > 8 ? 2 : 1),
+                SEEK_SET) < 0 ||
+            read(log->fd, buf, 1) != 1 || lseek(log->fd, -1, SEEK_CUR) < 0) {
+            deflateEnd(&strm);
+            return -1;
+        }
+        deflatePrime(&strm, (8 - log->back) & 7, *buf);
+
+        /* compress, finishing with a partial non-last empty static block */
+        strm.next_in = data;
+        max = (((uint)0 - 1) >> 1) + 1; /* in case int smaller than size_t */
+        do {
+            strm.avail_in = len > max ? max : (uint)len;
+            len -= strm.avail_in;
+            do {
+                strm.avail_out = DICT;
+                strm.next_out = buf;
+                deflate(&strm, len ? Z_NO_FLUSH : Z_PARTIAL_FLUSH);
+                got = DICT - strm.avail_out;
+                if (got && write(log->fd, buf, got) != got) {
+                    deflateEnd(&strm);
+                    return -1;
+                }
+                log_touch(log);
+            } while (strm.avail_out == 0);
+        } while (len);
+        deflateEnd(&strm);
+        BAIL(5);
+
+        /* find start of empty static block -- scanning backwards the first one
+           bit is the second bit of the block, if the last byte is zero, then
+           we know the byte before that has a one in the top bit, since an
+           empty static block is ten bits long */
+        if ((log->first = lseek(log->fd, -1, SEEK_CUR)) < 0 ||
+            read(log->fd, buf, 1) != 1)
+            return -1;
+        log->first++;
+        if (*buf) {
+            log->back = 1;
+            while ((*buf & ((uint)1 << (8 - log->back++))) == 0)
+                ;       /* guaranteed to terminate, since *buf != 0 */
+        }
+        else
+            log->back = 10;
+
+        /* update compressed crc and length */
+        log->ccrc = log->tcrc;
+        log->clen = log->tlen;
+    }
+    else {
+        /* no data to compress -- fix up existing gzip stream */
+        log->tcrc = log->ccrc;
+        log->tlen = log->clen;
+    }
+
+    /* complete and truncate gzip stream */
+    log->last = log->first;
+    log->stored = 0;
+    PUT4(buf, log->tcrc);
+    PUT4(buf + 4, log->tlen);
+    if (log_last(log, 1) || write(log->fd, buf, 8) != 8 ||
+        (end = lseek(log->fd, 0, SEEK_CUR)) < 0 || ftruncate(log->fd, end))
+        return -1;
+    BAIL(6);
+
+    /* mark as being in the replace operation */
+    if (log_mark(log, REPLACE_OP))
+        return -1;
+
+    /* execute the replace operation and mark the file as done */
+    return log_replace(log);
+}
+
+/* log a repair record to the .repairs file */
+local void log_log(struct log *log, int op, char *record)
+{
+    time_t now;
+    FILE *rec;
+
+    now = time(NULL);
+    strcpy(log->end, ".repairs");
+    rec = fopen(log->path, "a");
+    if (rec == NULL)
+        return;
+    fprintf(rec, "%.24s %s recovery: %s\n", ctime(&now), op == APPEND_OP ?
+            "append" : (op == COMPRESS_OP ? "compress" : "replace"), record);
+    fclose(rec);
+    return;
+}
+
+/* Recover the interrupted operation op.  First read foo.add for recovering an
+   append or compress operation.  Return -1 if there was an error reading or
+   writing foo.gz or reading an existing foo.add, or -2 if there was a memory
+   allocation failure. */
+local int log_recover(struct log *log, int op)
+{
+    int fd, ret = 0;
+    unsigned char *data = NULL;
+    size_t len = 0;
+    struct stat st;
+
+    /* log recovery */
+    log_log(log, op, "start");
+
+    /* load foo.add file if expected and present */
+    if (op == APPEND_OP || op == COMPRESS_OP) {
+        strcpy(log->end, ".add");
+        if (stat(log->path, &st) == 0 && st.st_size) {
+            len = (size_t)(st.st_size);
+            if (len != st.st_size || (data = malloc(st.st_size)) == NULL) {
+                log_log(log, op, "allocation failure");
+                return -2;
+            }
+            if ((fd = open(log->path, O_RDONLY, 0)) < 0) {
+                log_log(log, op, ".add file read failure");
+                return -1;
+            }
+            ret = read(fd, data, len) != len;
+            close(fd);
+            if (ret) {
+                log_log(log, op, ".add file read failure");
+                return -1;
+            }
+            log_log(log, op, "loaded .add file");
+        }
+        else
+            log_log(log, op, "missing .add file!");
+    }
+
+    /* recover the interrupted operation */
+    switch (op) {
+    case APPEND_OP:
+        ret = log_append(log, data, len);
+        break;
+    case COMPRESS_OP:
+        ret = log_compress(log, data, len);
+        break;
+    case REPLACE_OP:
+        ret = log_replace(log);
+    }
+
+    /* log status */
+    log_log(log, op, ret ? "failure" : "complete");
+
+    /* clean up */
+    if (data != NULL)
+        free(data);
+    return ret;
+}
+
+/* Close the foo.gz file (if open) and release the lock. */
+local void log_close(struct log *log)
+{
+    if (log->fd >= 0)
+        close(log->fd);
+    log->fd = -1;
+    log_unlock(log);
+}
+
+/* Open foo.gz, verify the header, and load the extra field contents, after
+   first creating the foo.lock file to gain exclusive access to the foo.*
+   files.  If foo.gz does not exist or is empty, then write the initial header,
+   extra, and body content of an empty foo.gz log file.  If there is an error
+   creating the lock file due to access restrictions, or an error reading or
+   writing the foo.gz file, or if the foo.gz file is not a proper log file for
+   this object (e.g. not a gzip file or does not contain the expected extra
+   field), then return true.  If there is an error, the lock is released.
+   Otherwise, the lock is left in place. */
+local int log_open(struct log *log)
+{
+    int op;
+
+    /* release open file resource if left over -- can occur if lock lost
+       between gzlog_open() and gzlog_write() */
+    if (log->fd >= 0)
+        close(log->fd);
+    log->fd = -1;
+
+    /* negotiate exclusive access */
+    if (log_lock(log) < 0)
+        return -1;
+
+    /* open the log file, foo.gz */
+    strcpy(log->end, ".gz");
+    log->fd = open(log->path, O_RDWR | O_CREAT, 0644);
+    if (log->fd < 0) {
+        log_close(log);
+        return -1;
+    }
+
+    /* if new, initialize foo.gz with an empty log, delete old dictionary */
+    if (lseek(log->fd, 0, SEEK_END) == 0) {
+        if (write(log->fd, log_gzhead, HEAD) != HEAD ||
+            write(log->fd, log_gzext, EXTRA) != EXTRA ||
+            write(log->fd, log_gzbody, BODY) != BODY) {
+            log_close(log);
+            return -1;
+        }
+        strcpy(log->end, ".dict");
+        unlink(log->path);
+    }
+
+    /* verify log file and load extra field information */
+    if ((op = log_head(log)) < 0) {
+        log_close(log);
+        return -1;
+    }
+
+    /* check for interrupted process and if so, recover */
+    if (op != NO_OP && log_recover(log, op)) {
+        log_close(log);
+        return -1;
+    }
+
+    /* touch the lock file to prevent another process from grabbing it */
+    log_touch(log);
+    return 0;
+}
+
+/* See gzlog.h for the description of the external methods below */
+gzlog *gzlog_open(char *path)
+{
+    size_t n;
+    struct log *log;
+
+    /* check arguments */
+    if (path == NULL || *path == 0)
+        return NULL;
+
+    /* allocate and initialize log structure */
+    log = malloc(sizeof(struct log));
+    if (log == NULL)
+        return NULL;
+    strcpy(log->id, LOGID);
+    log->fd = -1;
+
+    /* save path and end of path for name construction */
+    n = strlen(path);
+    log->path = malloc(n + 9);              /* allow for ".repairs" */
+    if (log->path == NULL) {
+        free(log);
+        return NULL;
+    }
+    strcpy(log->path, path);
+    log->end = log->path + n;
+
+    /* gain exclusive access and verify log file -- may perform a
+       recovery operation if needed */
+    if (log_open(log)) {
+        free(log->path);
+        free(log);
+        return NULL;
+    }
+
+    /* return pointer to log structure */
+    return log;
+}
+
+/* gzlog_compress() return values:
+    0: all good
+   -1: file i/o error (usually access issue)
+   -2: memory allocation failure
+   -3: invalid log pointer argument */
+int gzlog_compress(gzlog *logd)
+{
+    int fd, ret;
+    uint block;
+    size_t len, next;
+    unsigned char *data, buf[5];
+    struct log *log = logd;
+
+    /* check arguments */
+    if (log == NULL || strcmp(log->id, LOGID) || len < 0)
+        return -3;
+
+    /* see if we lost the lock -- if so get it again and reload the extra
+       field information (it probably changed), recover last operation if
+       necessary */
+    if (log_check(log) && log_open(log))
+        return -1;
+
+    /* create space for uncompressed data */
+    len = ((size_t)(log->last - log->first) & ~(((size_t)1 << 10) - 1)) +
+          log->stored;
+    if ((data = malloc(len)) == NULL)
+        return -2;
+
+    /* do statement here is just a cheap trick for error handling */
+    do {
+        /* read in the uncompressed data */
+        if (lseek(log->fd, log->first - 1, SEEK_SET) < 0)
+            break;
+        next = 0;
+        while (next < len) {
+            if (read(log->fd, buf, 5) != 5)
+                break;
+            block = PULL2(buf + 1);
+            if (next + block > len ||
+                read(log->fd, (char *)data + next, block) != block)
+                break;
+            next += block;
+        }
+        if (lseek(log->fd, 0, SEEK_CUR) != log->last + 4 + log->stored)
+            break;
+        log_touch(log);
+
+        /* write the uncompressed data to the .add file */
+        strcpy(log->end, ".add");
+        fd = open(log->path, O_WRONLY | O_CREAT | O_TRUNC, 0644);
+        if (fd < 0)
+            break;
+        ret = write(fd, data, len) != len;
+        if (ret | close(fd))
+            break;
+        log_touch(log);
+
+        /* write the dictionary for the next compress to the .temp file */
+        strcpy(log->end, ".temp");
+        fd = open(log->path, O_WRONLY | O_CREAT | O_TRUNC, 0644);
+        if (fd < 0)
+            break;
+        next = DICT > len ? len : DICT;
+        ret = write(fd, (char *)data + len - next, next) != next;
+        if (ret | close(fd))
+            break;
+        log_touch(log);
+
+        /* roll back to compressed data, mark the compress in progress */
+        log->last = log->first;
+        log->stored = 0;
+        if (log_mark(log, COMPRESS_OP))
+            break;
+        BAIL(7);
+
+        /* compress and append the data (clears mark) */
+        ret = log_compress(log, data, len);
+        free(data);
+        return ret;
+    } while (0);
+
+    /* broke out of do above on i/o error */
+    free(data);
+    return -1;
+}
+
+/* gzlog_write() return values:
+    0: all good
+   -1: file i/o error (usually access issue)
+   -2: memory allocation failure
+   -3: invalid log pointer argument */
+int gzlog_write(gzlog *logd, void *data, size_t len)
+{
+    int fd, ret;
+    struct log *log = logd;
+
+    /* check arguments */
+    if (log == NULL || strcmp(log->id, LOGID) || len < 0)
+        return -3;
+    if (data == NULL || len == 0)
+        return 0;
+
+    /* see if we lost the lock -- if so get it again and reload the extra
+       field information (it probably changed), recover last operation if
+       necessary */
+    if (log_check(log) && log_open(log))
+        return -1;
+
+    /* create and write .add file */
+    strcpy(log->end, ".add");
+    fd = open(log->path, O_WRONLY | O_CREAT | O_TRUNC, 0644);
+    if (fd < 0)
+        return -1;
+    ret = write(fd, data, len) != len;
+    if (ret | close(fd))
+        return -1;
+    log_touch(log);
+
+    /* mark log file with append in progress */
+    if (log_mark(log, APPEND_OP))
+        return -1;
+    BAIL(8);
+
+    /* append data (clears mark) */
+    if (log_append(log, data, len))
+        return -1;
+
+    /* check to see if it's time to compress -- if not, then done */
+    if (((log->last - log->first) >> 10) + (log->stored >> 10) < TRIGGER)
+        return 0;
+
+    /* time to compress */
+    return gzlog_compress(log);
+}
+
+/* gzlog_close() return values:
+    0: ok
+   -3: invalid log pointer argument */
+int gzlog_close(gzlog *logd)
+{
+    struct log *log = logd;
+
+    /* check arguments */
+    if (log == NULL || strcmp(log->id, LOGID))
+        return -3;
+
+    /* close the log file and release the lock */
+    log_close(log);
+
+    /* free structure and return */
+    if (log->path != NULL)
+        free(log->path);
+    strcpy(log->id, "bad");
+    free(log);
+    return 0;
+}
diff --git a/zlib/examples/gzlog.h b/zlib/examples/gzlog.h
new file mode 100644
index 0000000..c461426
--- /dev/null
+++ b/zlib/examples/gzlog.h
@@ -0,0 +1,89 @@
+/* gzlog.h
+  Copyright (C) 2004, 2008 Mark Adler, all rights reserved
+  version 2.0, 25 Apr 2008
+
+  This software is provided 'as-is', without any express or implied
+  warranty.  In no event will the author be held liable for any damages
+  arising from the use of this software.
+
+  Permission is granted to anyone to use this software for any purpose,
+  including commercial applications, and to alter it and redistribute it
+  freely, subject to the following restrictions:
+
+  1. The origin of this software must not be misrepresented; you must not
+     claim that you wrote the original software. If you use this software
+     in a product, an acknowledgment in the product documentation would be
+     appreciated but is not required.
+  2. Altered source versions must be plainly marked as such, and must not be
+     misrepresented as being the original software.
+  3. This notice may not be removed or altered from any source distribution.
+
+  Mark Adler    madler@alumni.caltech.edu
+ */
+
+/* Version History:
+   1.0  26 Nov 2004  First version
+   2.0  25 Apr 2008  Complete redesign for recovery of interrupted operations
+                     Interface changed slightly in that now path is a prefix
+                     Compression now occurs as needed during gzlog_write()
+                     gzlog_write() now always leaves the log file as valid gzip
+ */
+
+/*
+   The gzlog object allows writing short messages to a gzipped log file,
+   opening the log file locked for small bursts, and then closing it.  The log
+   object works by appending stored (uncompressed) data to the gzip file until
+   1 MB has been accumulated.  At that time, the stored data is compressed, and
+   replaces the uncompressed data in the file.  The log file is truncated to
+   its new size at that time.  After each write operation, the log file is a
+   valid gzip file that can decompressed to recover what was written.
+
+   The gzlog operations can be interupted at any point due to an application or
+   system crash, and the log file will be recovered the next time the log is
+   opened with gzlog_open().
+ */
+
+#ifndef GZLOG_H
+#define GZLOG_H
+
+/* gzlog object type */
+typedef void gzlog;
+
+/* Open a gzlog object, creating the log file if it does not exist.  Return
+   NULL on error.  Note that gzlog_open() could take a while to complete if it
+   has to wait to verify that a lock is stale (possibly for five minutes), or
+   if there is significant contention with other instantiations of this object
+   when locking the resource.  path is the prefix of the file names created by
+   this object.  If path is "foo", then the log file will be "foo.gz", and
+   other auxiliary files will be created and destroyed during the process:
+   "foo.dict" for a compression dictionary, "foo.temp" for a temporary (next)
+   dictionary, "foo.add" for data being added or compressed, "foo.lock" for the
+   lock file, and "foo.repairs" to log recovery operations performed due to
+   interrupted gzlog operations.  A gzlog_open() followed by a gzlog_close()
+   will recover a previously interrupted operation, if any. */
+gzlog *gzlog_open(char *path);
+
+/* Write to a gzlog object.  Return zero on success, -1 if there is a file i/o
+   error on any of the gzlog files (this should not happen if gzlog_open()
+   succeeded, unless the device has run out of space or leftover auxiliary
+   files have permissions or ownership that prevent their use), -2 if there is
+   a memory allocation failure, or -3 if the log argument is invalid (e.g. if
+   it was not created by gzlog_open()).  This function will write data to the
+   file uncompressed, until 1 MB has been accumulated, at which time that data
+   will be compressed.  The log file will be a valid gzip file upon successful
+   return. */
+int gzlog_write(gzlog *log, void *data, size_t len);
+
+/* Force compression of any uncompressed data in the log.  This should be used
+   sparingly, if at all.  The main application would be when a log file will
+   not be appended to again.  If this is used to compress frequently while
+   appending, it will both significantly increase the execution time and
+   reduce the compression ratio.  The return codes are the same as for
+   gzlog_write(). */
+int gzlog_compress(gzlog *log);
+
+/* Close a gzlog object.  Return zero on success, -3 if the log argument is
+   invalid.  The log object is freed, and so cannot be referenced again. */
+int gzlog_close(gzlog *log);
+
+#endif
diff --git a/zlib/examples/zlib_how.html b/zlib/examples/zlib_how.html
new file mode 100644
index 0000000..444ff1c
--- /dev/null
+++ b/zlib/examples/zlib_how.html
@@ -0,0 +1,545 @@
+<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN"
+  "http://www.w3.org/TR/REC-html40/loose.dtd">
+<html>
+<head>
+<meta http-equiv="Content-Type" content="text/html; charset=ISO-8859-1">
+<title>zlib Usage Example</title>
+<!--  Copyright (c) 2004, 2005 Mark Adler.  -->
+</head>
+<body bgcolor="#FFFFFF" text="#000000" link="#0000FF" vlink="#00A000">
+<h2 align="center"> zlib Usage Example </h2>
+We often get questions about how the <tt>deflate()</tt> and <tt>inflate()</tt> functions should be used.
+Users wonder when they should provide more input, when they should use more output,
+what to do with a <tt>Z_BUF_ERROR</tt>, how to make sure the process terminates properly, and
+so on.  So for those who have read <tt>zlib.h</tt> (a few times), and
+would like further edification, below is an annotated example in C of simple routines to compress and decompress
+from an input file to an output file using <tt>deflate()</tt> and <tt>inflate()</tt> respectively.  The
+annotations are interspersed between lines of the code.  So please read between the lines.
+We hope this helps explain some of the intricacies of <em>zlib</em>.
+<p>
+Without further adieu, here is the program <a href="zpipe.c"><tt>zpipe.c</tt></a>:
+<pre><b>
+/* zpipe.c: example of proper use of zlib's inflate() and deflate()
+   Not copyrighted -- provided to the public domain
+   Version 1.4  11 December 2005  Mark Adler */
+
+/* Version history:
+   1.0  30 Oct 2004  First version
+   1.1   8 Nov 2004  Add void casting for unused return values
+                     Use switch statement for inflate() return values
+   1.2   9 Nov 2004  Add assertions to document zlib guarantees
+   1.3   6 Apr 2005  Remove incorrect assertion in inf()
+   1.4  11 Dec 2005  Add hack to avoid MSDOS end-of-line conversions
+                     Avoid some compiler warnings for input and output buffers
+ */
+</b></pre><!-- -->
+We now include the header files for the required definitions.  From
+<tt>stdio.h</tt> we use <tt>fopen()</tt>, <tt>fread()</tt>, <tt>fwrite()</tt>,
+<tt>feof()</tt>, <tt>ferror()</tt>, and <tt>fclose()</tt> for file i/o, and
+<tt>fputs()</tt> for error messages.  From <tt>string.h</tt> we use
+<tt>strcmp()</tt> for command line argument processing.
+From <tt>assert.h</tt> we use the <tt>assert()</tt> macro.
+From <tt>zlib.h</tt>
+we use the basic compression functions <tt>deflateInit()</tt>,
+<tt>deflate()</tt>, and <tt>deflateEnd()</tt>, and the basic decompression
+functions <tt>inflateInit()</tt>, <tt>inflate()</tt>, and
+<tt>inflateEnd()</tt>.
+<pre><b>
+#include &lt;stdio.h&gt;
+#include &lt;string.h&gt;
+#include &lt;assert.h&gt;
+#include "zlib.h"
+</b></pre><!-- -->
+This is an ugly hack required to avoid corruption of the input and output data on
+Windows/MS-DOS systems.  Without this, those systems would assume that the input and output
+files are text, and try to convert the end-of-line characters from one standard to
+another.  That would corrupt binary data, and in particular would render the compressed data unusable.
+This sets the input and output to binary which suppresses the end-of-line conversions.
+<tt>SET_BINARY_MODE()</tt> will be used later on <tt>stdin</tt> and <tt>stdout</tt>, at the beginning of <tt>main()</tt>.
+<pre><b>
+#if defined(MSDOS) || defined(OS2) || defined(WIN32) || defined(__CYGWIN__)
+#  include &lt;fcntl.h&gt;
+#  include &lt;io.h&gt;
+#  define SET_BINARY_MODE(file) setmode(fileno(file), O_BINARY)
+#else
+#  define SET_BINARY_MODE(file)
+#endif
+</b></pre><!-- -->
+<tt>CHUNK</tt> is simply the buffer size for feeding data to and pulling data
+from the <em>zlib</em> routines.  Larger buffer sizes would be more efficient,
+especially for <tt>inflate()</tt>.  If the memory is available, buffers sizes
+on the order of 128K or 256K bytes should be used.
+<pre><b>
+#define CHUNK 16384
+</b></pre><!-- -->
+The <tt>def()</tt> routine compresses data from an input file to an output file.  The output data
+will be in the <em>zlib</em> format, which is different from the <em>gzip</em> or <em>zip</em>
+formats.  The <em>zlib</em> format has a very small header of only two bytes to identify it as
+a <em>zlib</em> stream and to provide decoding information, and a four-byte trailer with a fast
+check value to verify the integrity of the uncompressed data after decoding.
+<pre><b>
+/* Compress from file source to file dest until EOF on source.
+   def() returns Z_OK on success, Z_MEM_ERROR if memory could not be
+   allocated for processing, Z_STREAM_ERROR if an invalid compression
+   level is supplied, Z_VERSION_ERROR if the version of zlib.h and the
+   version of the library linked do not match, or Z_ERRNO if there is
+   an error reading or writing the files. */
+int def(FILE *source, FILE *dest, int level)
+{
+</b></pre>
+Here are the local variables for <tt>def()</tt>.  <tt>ret</tt> will be used for <em>zlib</em>
+return codes.  <tt>flush</tt> will keep track of the current flushing state for <tt>deflate()</tt>,
+which is either no flushing, or flush to completion after the end of the input file is reached.
+<tt>have</tt> is the amount of data returned from <tt>deflate()</tt>.  The <tt>strm</tt> structure
+is used to pass information to and from the <em>zlib</em> routines, and to maintain the
+<tt>deflate()</tt> state.  <tt>in</tt> and <tt>out</tt> are the input and output buffers for
+<tt>deflate()</tt>.
+<pre><b>
+    int ret, flush;
+    unsigned have;
+    z_stream strm;
+    unsigned char in[CHUNK];
+    unsigned char out[CHUNK];
+</b></pre><!-- -->
+The first thing we do is to initialize the <em>zlib</em> state for compression using
+<tt>deflateInit()</tt>.  This must be done before the first use of <tt>deflate()</tt>.
+The <tt>zalloc</tt>, <tt>zfree</tt>, and <tt>opaque</tt> fields in the <tt>strm</tt>
+structure must be initialized before calling <tt>deflateInit()</tt>.  Here they are
+set to the <em>zlib</em> constant <tt>Z_NULL</tt> to request that <em>zlib</em> use
+the default memory allocation routines.  An application may also choose to provide
+custom memory allocation routines here.  <tt>deflateInit()</tt> will allocate on the
+order of 256K bytes for the internal state.
+(See <a href="zlib_tech.html"><em>zlib Technical Details</em></a>.)
+<p>
+<tt>deflateInit()</tt> is called with a pointer to the structure to be initialized and
+the compression level, which is an integer in the range of -1 to 9.  Lower compression
+levels result in faster execution, but less compression.  Higher levels result in
+greater compression, but slower execution.  The <em>zlib</em> constant Z_DEFAULT_COMPRESSION,
+equal to -1,
+provides a good compromise between compression and speed and is equivalent to level 6.
+Level 0 actually does no compression at all, and in fact expands the data slightly to produce
+the <em>zlib</em> format (it is not a byte-for-byte copy of the input).
+More advanced applications of <em>zlib</em>
+may use <tt>deflateInit2()</tt> here instead.  Such an application may want to reduce how
+much memory will be used, at some price in compression.  Or it may need to request a
+<em>gzip</em> header and trailer instead of a <em>zlib</em> header and trailer, or raw
+encoding with no header or trailer at all.
+<p>
+We must check the return value of <tt>deflateInit()</tt> against the <em>zlib</em> constant
+<tt>Z_OK</tt> to make sure that it was able to
+allocate memory for the internal state, and that the provided arguments were valid.
+<tt>deflateInit()</tt> will also check that the version of <em>zlib</em> that the <tt>zlib.h</tt>
+file came from matches the version of <em>zlib</em> actually linked with the program.  This
+is especially important for environments in which <em>zlib</em> is a shared library.
+<p>
+Note that an application can initialize multiple, independent <em>zlib</em> streams, which can
+operate in parallel.  The state information maintained in the structure allows the <em>zlib</em>
+routines to be reentrant.
+<pre><b>
+    /* allocate deflate state */
+    strm.zalloc = Z_NULL;
+    strm.zfree = Z_NULL;
+    strm.opaque = Z_NULL;
+    ret = deflateInit(&amp;strm, level);
+    if (ret != Z_OK)
+        return ret;
+</b></pre><!-- -->
+With the pleasantries out of the way, now we can get down to business.  The outer <tt>do</tt>-loop
+reads all of the input file and exits at the bottom of the loop once end-of-file is reached.
+This loop contains the only call of <tt>deflate()</tt>.  So we must make sure that all of the
+input data has been processed and that all of the output data has been generated and consumed
+before we fall out of the loop at the bottom.
+<pre><b>
+    /* compress until end of file */
+    do {
+</b></pre>
+We start off by reading data from the input file.  The number of bytes read is put directly
+into <tt>avail_in</tt>, and a pointer to those bytes is put into <tt>next_in</tt>.  We also
+check to see if end-of-file on the input has been reached.  If we are at the end of file, then <tt>flush</tt> is set to the
+<em>zlib</em> constant <tt>Z_FINISH</tt>, which is later passed to <tt>deflate()</tt> to
+indicate that this is the last chunk of input data to compress.  We need to use <tt>feof()</tt>
+to check for end-of-file as opposed to seeing if fewer than <tt>CHUNK</tt> bytes have been read.  The
+reason is that if the input file length is an exact multiple of <tt>CHUNK</tt>, we will miss
+the fact that we got to the end-of-file, and not know to tell <tt>deflate()</tt> to finish
+up the compressed stream.  If we are not yet at the end of the input, then the <em>zlib</em>
+constant <tt>Z_NO_FLUSH</tt> will be passed to <tt>deflate</tt> to indicate that we are still
+in the middle of the uncompressed data.
+<p>
+If there is an error in reading from the input file, the process is aborted with
+<tt>deflateEnd()</tt> being called to free the allocated <em>zlib</em> state before returning
+the error.  We wouldn't want a memory leak, now would we?  <tt>deflateEnd()</tt> can be called
+at any time after the state has been initialized.  Once that's done, <tt>deflateInit()</tt> (or
+<tt>deflateInit2()</tt>) would have to be called to start a new compression process.  There is
+no point here in checking the <tt>deflateEnd()</tt> return code.  The deallocation can't fail.
+<pre><b>
+        strm.avail_in = fread(in, 1, CHUNK, source);
+        if (ferror(source)) {
+            (void)deflateEnd(&amp;strm);
+            return Z_ERRNO;
+        }
+        flush = feof(source) ? Z_FINISH : Z_NO_FLUSH;
+        strm.next_in = in;
+</b></pre><!-- -->
+The inner <tt>do</tt>-loop passes our chunk of input data to <tt>deflate()</tt>, and then
+keeps calling <tt>deflate()</tt> until it is done producing output.  Once there is no more
+new output, <tt>deflate()</tt> is guaranteed to have consumed all of the input, i.e.,
+<tt>avail_in</tt> will be zero.
+<pre><b>
+        /* run deflate() on input until output buffer not full, finish
+           compression if all of source has been read in */
+        do {
+</b></pre>
+Output space is provided to <tt>deflate()</tt> by setting <tt>avail_out</tt> to the number
+of available output bytes and <tt>next_out</tt> to a pointer to that space.
+<pre><b>
+            strm.avail_out = CHUNK;
+            strm.next_out = out;
+</b></pre>
+Now we call the compression engine itself, <tt>deflate()</tt>.  It takes as many of the
+<tt>avail_in</tt> bytes at <tt>next_in</tt> as it can process, and writes as many as
+<tt>avail_out</tt> bytes to <tt>next_out</tt>.  Those counters and pointers are then
+updated past the input data consumed and the output data written.  It is the amount of
+output space available that may limit how much input is consumed.
+Hence the inner loop to make sure that
+all of the input is consumed by providing more output space each time.  Since <tt>avail_in</tt>
+and <tt>next_in</tt> are updated by <tt>deflate()</tt>, we don't have to mess with those
+between <tt>deflate()</tt> calls until it's all used up.
+<p>
+The parameters to <tt>deflate()</tt> are a pointer to the <tt>strm</tt> structure containing
+the input and output information and the internal compression engine state, and a parameter
+indicating whether and how to flush data to the output.  Normally <tt>deflate</tt> will consume
+several K bytes of input data before producing any output (except for the header), in order
+to accumulate statistics on the data for optimum compression.  It will then put out a burst of
+compressed data, and proceed to consume more input before the next burst.  Eventually,
+<tt>deflate()</tt>
+must be told to terminate the stream, complete the compression with provided input data, and
+write out the trailer check value.  <tt>deflate()</tt> will continue to compress normally as long
+as the flush parameter is <tt>Z_NO_FLUSH</tt>.  Once the <tt>Z_FINISH</tt> parameter is provided,
+<tt>deflate()</tt> will begin to complete the compressed output stream.  However depending on how
+much output space is provided, <tt>deflate()</tt> may have to be called several times until it
+has provided the complete compressed stream, even after it has consumed all of the input.  The flush
+parameter must continue to be <tt>Z_FINISH</tt> for those subsequent calls.
+<p>
+There are other values of the flush parameter that are used in more advanced applications.  You can
+force <tt>deflate()</tt> to produce a burst of output that encodes all of the input data provided
+so far, even if it wouldn't have otherwise, for example to control data latency on a link with
+compressed data.  You can also ask that <tt>deflate()</tt> do that as well as erase any history up to
+that point so that what follows can be decompressed independently, for example for random access
+applications.  Both requests will degrade compression by an amount depending on how often such
+requests are made.
+<p>
+<tt>deflate()</tt> has a return value that can indicate errors, yet we do not check it here.  Why
+not?  Well, it turns out that <tt>deflate()</tt> can do no wrong here.  Let's go through
+<tt>deflate()</tt>'s return values and dispense with them one by one.  The possible values are
+<tt>Z_OK</tt>, <tt>Z_STREAM_END</tt>, <tt>Z_STREAM_ERROR</tt>, or <tt>Z_BUF_ERROR</tt>.  <tt>Z_OK</tt>
+is, well, ok.  <tt>Z_STREAM_END</tt> is also ok and will be returned for the last call of
+<tt>deflate()</tt>.  This is already guaranteed by calling <tt>deflate()</tt> with <tt>Z_FINISH</tt>
+until it has no more output.  <tt>Z_STREAM_ERROR</tt> is only possible if the stream is not
+initialized properly, but we did initialize it properly.  There is no harm in checking for
+<tt>Z_STREAM_ERROR</tt> here, for example to check for the possibility that some
+other part of the application inadvertently clobbered the memory containing the <em>zlib</em> state.
+<tt>Z_BUF_ERROR</tt> will be explained further below, but
+suffice it to say that this is simply an indication that <tt>deflate()</tt> could not consume
+more input or produce more output.  <tt>deflate()</tt> can be called again with more output space
+or more available input, which it will be in this code.
+<pre><b>
+            ret = deflate(&amp;strm, flush);    /* no bad return value */
+            assert(ret != Z_STREAM_ERROR);  /* state not clobbered */
+</b></pre>
+Now we compute how much output <tt>deflate()</tt> provided on the last call, which is the
+difference between how much space was provided before the call, and how much output space
+is still available after the call.  Then that data, if any, is written to the output file.
+We can then reuse the output buffer for the next call of <tt>deflate()</tt>.  Again if there
+is a file i/o error, we call <tt>deflateEnd()</tt> before returning to avoid a memory leak.
+<pre><b>
+            have = CHUNK - strm.avail_out;
+            if (fwrite(out, 1, have, dest) != have || ferror(dest)) {
+                (void)deflateEnd(&amp;strm);
+                return Z_ERRNO;
+            }
+</b></pre>
+The inner <tt>do</tt>-loop is repeated until the last <tt>deflate()</tt> call fails to fill the
+provided output buffer.  Then we know that <tt>deflate()</tt> has done as much as it can with
+the provided input, and that all of that input has been consumed.  We can then fall out of this
+loop and reuse the input buffer.
+<p>
+The way we tell that <tt>deflate()</tt> has no more output is by seeing that it did not fill
+the output buffer, leaving <tt>avail_out</tt> greater than zero.  However suppose that
+<tt>deflate()</tt> has no more output, but just so happened to exactly fill the output buffer!
+<tt>avail_out</tt> is zero, and we can't tell that <tt>deflate()</tt> has done all it can.
+As far as we know, <tt>deflate()</tt>
+has more output for us.  So we call it again.  But now <tt>deflate()</tt> produces no output
+at all, and <tt>avail_out</tt> remains unchanged as <tt>CHUNK</tt>.  That <tt>deflate()</tt> call
+wasn't able to do anything, either consume input or produce output, and so it returns
+<tt>Z_BUF_ERROR</tt>.  (See, I told you I'd cover this later.)  However this is not a problem at
+all.  Now we finally have the desired indication that <tt>deflate()</tt> is really done,
+and so we drop out of the inner loop to provide more input to <tt>deflate()</tt>.
+<p>
+With <tt>flush</tt> set to <tt>Z_FINISH</tt>, this final set of <tt>deflate()</tt> calls will
+complete the output stream.  Once that is done, subsequent calls of <tt>deflate()</tt> would return
+<tt>Z_STREAM_ERROR</tt> if the flush parameter is not <tt>Z_FINISH</tt>, and do no more processing
+until the state is reinitialized.
+<p>
+Some applications of <em>zlib</em> have two loops that call <tt>deflate()</tt>
+instead of the single inner loop we have here.  The first loop would call
+without flushing and feed all of the data to <tt>deflate()</tt>.  The second loop would call
+<tt>deflate()</tt> with no more
+data and the <tt>Z_FINISH</tt> parameter to complete the process.  As you can see from this
+example, that can be avoided by simply keeping track of the current flush state.
+<pre><b>
+        } while (strm.avail_out == 0);
+        assert(strm.avail_in == 0);     /* all input will be used */
+</b></pre><!-- -->
+Now we check to see if we have already processed all of the input file.  That information was
+saved in the <tt>flush</tt> variable, so we see if that was set to <tt>Z_FINISH</tt>.  If so,
+then we're done and we fall out of the outer loop.  We're guaranteed to get <tt>Z_STREAM_END</tt>
+from the last <tt>deflate()</tt> call, since we ran it until the last chunk of input was
+consumed and all of the output was generated.
+<pre><b>
+        /* done when last data in file processed */
+    } while (flush != Z_FINISH);
+    assert(ret == Z_STREAM_END);        /* stream will be complete */
+</b></pre><!-- -->
+The process is complete, but we still need to deallocate the state to avoid a memory leak
+(or rather more like a memory hemorrhage if you didn't do this).  Then
+finally we can return with a happy return value.
+<pre><b>
+    /* clean up and return */
+    (void)deflateEnd(&amp;strm);
+    return Z_OK;
+}
+</b></pre><!-- -->
+Now we do the same thing for decompression in the <tt>inf()</tt> routine. <tt>inf()</tt>
+decompresses what is hopefully a valid <em>zlib</em> stream from the input file and writes the
+uncompressed data to the output file.  Much of the discussion above for <tt>def()</tt>
+applies to <tt>inf()</tt> as well, so the discussion here will focus on the differences between
+the two.
+<pre><b>
+/* Decompress from file source to file dest until stream ends or EOF.
+   inf() returns Z_OK on success, Z_MEM_ERROR if memory could not be
+   allocated for processing, Z_DATA_ERROR if the deflate data is
+   invalid or incomplete, Z_VERSION_ERROR if the version of zlib.h and
+   the version of the library linked do not match, or Z_ERRNO if there
+   is an error reading or writing the files. */
+int inf(FILE *source, FILE *dest)
+{
+</b></pre>
+The local variables have the same functionality as they do for <tt>def()</tt>.  The
+only difference is that there is no <tt>flush</tt> variable, since <tt>inflate()</tt>
+can tell from the <em>zlib</em> stream itself when the stream is complete.
+<pre><b>
+    int ret;
+    unsigned have;
+    z_stream strm;
+    unsigned char in[CHUNK];
+    unsigned char out[CHUNK];
+</b></pre><!-- -->
+The initialization of the state is the same, except that there is no compression level,
+of course, and two more elements of the structure are initialized.  <tt>avail_in</tt>
+and <tt>next_in</tt> must be initialized before calling <tt>inflateInit()</tt>.  This
+is because the application has the option to provide the start of the zlib stream in
+order for <tt>inflateInit()</tt> to have access to information about the compression
+method to aid in memory allocation.  In the current implementation of <em>zlib</em>
+(up through versions 1.2.x), the method-dependent memory allocations are deferred to the first call of
+<tt>inflate()</tt> anyway.  However those fields must be initialized since later versions
+of <em>zlib</em> that provide more compression methods may take advantage of this interface.
+In any case, no decompression is performed by <tt>inflateInit()</tt>, so the
+<tt>avail_out</tt> and <tt>next_out</tt> fields do not need to be initialized before calling.
+<p>
+Here <tt>avail_in</tt> is set to zero and <tt>next_in</tt> is set to <tt>Z_NULL</tt> to
+indicate that no input data is being provided.
+<pre><b>
+    /* allocate inflate state */
+    strm.zalloc = Z_NULL;
+    strm.zfree = Z_NULL;
+    strm.opaque = Z_NULL;
+    strm.avail_in = 0;
+    strm.next_in = Z_NULL;
+    ret = inflateInit(&amp;strm);
+    if (ret != Z_OK)
+        return ret;
+</b></pre><!-- -->
+The outer <tt>do</tt>-loop decompresses input until <tt>inflate()</tt> indicates
+that it has reached the end of the compressed data and has produced all of the uncompressed
+output.  This is in contrast to <tt>def()</tt> which processes all of the input file.
+If end-of-file is reached before the compressed data self-terminates, then the compressed
+data is incomplete and an error is returned.
+<pre><b>
+    /* decompress until deflate stream ends or end of file */
+    do {
+</b></pre>
+We read input data and set the <tt>strm</tt> structure accordingly.  If we've reached the
+end of the input file, then we leave the outer loop and report an error, since the
+compressed data is incomplete.  Note that we may read more data than is eventually consumed
+by <tt>inflate()</tt>, if the input file continues past the <em>zlib</em> stream.
+For applications where <em>zlib</em> streams are embedded in other data, this routine would
+need to be modified to return the unused data, or at least indicate how much of the input
+data was not used, so the application would know where to pick up after the <em>zlib</em> stream.
+<pre><b>
+        strm.avail_in = fread(in, 1, CHUNK, source);
+        if (ferror(source)) {
+            (void)inflateEnd(&amp;strm);
+            return Z_ERRNO;
+        }
+        if (strm.avail_in == 0)
+            break;
+        strm.next_in = in;
+</b></pre><!-- -->
+The inner <tt>do</tt>-loop has the same function it did in <tt>def()</tt>, which is to
+keep calling <tt>inflate()</tt> until has generated all of the output it can with the
+provided input.
+<pre><b>
+        /* run inflate() on input until output buffer not full */
+        do {
+</b></pre>
+Just like in <tt>def()</tt>, the same output space is provided for each call of <tt>inflate()</tt>.
+<pre><b>
+            strm.avail_out = CHUNK;
+            strm.next_out = out;
+</b></pre>
+Now we run the decompression engine itself.  There is no need to adjust the flush parameter, since
+the <em>zlib</em> format is self-terminating. The main difference here is that there are
+return values that we need to pay attention to.  <tt>Z_DATA_ERROR</tt>
+indicates that <tt>inflate()</tt> detected an error in the <em>zlib</em> compressed data format,
+which means that either the data is not a <em>zlib</em> stream to begin with, or that the data was
+corrupted somewhere along the way since it was compressed.  The other error to be processed is
+<tt>Z_MEM_ERROR</tt>, which can occur since memory allocation is deferred until <tt>inflate()</tt>
+needs it, unlike <tt>deflate()</tt>, whose memory is allocated at the start by <tt>deflateInit()</tt>.
+<p>
+Advanced applications may use
+<tt>deflateSetDictionary()</tt> to prime <tt>deflate()</tt> with a set of likely data to improve the
+first 32K or so of compression.  This is noted in the <em>zlib</em> header, so <tt>inflate()</tt>
+requests that that dictionary be provided before it can start to decompress.  Without the dictionary,
+correct decompression is not possible.  For this routine, we have no idea what the dictionary is,
+so the <tt>Z_NEED_DICT</tt> indication is converted to a <tt>Z_DATA_ERROR</tt>.
+<p>
+<tt>inflate()</tt> can also return <tt>Z_STREAM_ERROR</tt>, which should not be possible here,
+but could be checked for as noted above for <tt>def()</tt>.  <tt>Z_BUF_ERROR</tt> does not need to be
+checked for here, for the same reasons noted for <tt>def()</tt>.  <tt>Z_STREAM_END</tt> will be
+checked for later.
+<pre><b>
+            ret = inflate(&amp;strm, Z_NO_FLUSH);
+            assert(ret != Z_STREAM_ERROR);  /* state not clobbered */
+            switch (ret) {
+            case Z_NEED_DICT:
+                ret = Z_DATA_ERROR;     /* and fall through */
+            case Z_DATA_ERROR:
+            case Z_MEM_ERROR:
+                (void)inflateEnd(&amp;strm);
+                return ret;
+            }
+</b></pre>
+The output of <tt>inflate()</tt> is handled identically to that of <tt>deflate()</tt>.
+<pre><b>
+            have = CHUNK - strm.avail_out;
+            if (fwrite(out, 1, have, dest) != have || ferror(dest)) {
+                (void)inflateEnd(&amp;strm);
+                return Z_ERRNO;
+            }
+</b></pre>
+The inner <tt>do</tt>-loop ends when <tt>inflate()</tt> has no more output as indicated
+by not filling the output buffer, just as for <tt>deflate()</tt>.  In this case, we cannot
+assert that <tt>strm.avail_in</tt> will be zero, since the deflate stream may end before the file
+does.
+<pre><b>
+        } while (strm.avail_out == 0);
+</b></pre><!-- -->
+The outer <tt>do</tt>-loop ends when <tt>inflate()</tt> reports that it has reached the
+end of the input <em>zlib</em> stream, has completed the decompression and integrity
+check, and has provided all of the output.  This is indicated by the <tt>inflate()</tt>
+return value <tt>Z_STREAM_END</tt>.  The inner loop is guaranteed to leave <tt>ret</tt>
+equal to <tt>Z_STREAM_END</tt> if the last chunk of the input file read contained the end
+of the <em>zlib</em> stream.  So if the return value is not <tt>Z_STREAM_END</tt>, the
+loop continues to read more input.
+<pre><b>
+        /* done when inflate() says it's done */
+    } while (ret != Z_STREAM_END);
+</b></pre><!-- -->
+At this point, decompression successfully completed, or we broke out of the loop due to no
+more data being available from the input file.  If the last <tt>inflate()</tt> return value
+is not <tt>Z_STREAM_END</tt>, then the <em>zlib</em> stream was incomplete and a data error
+is returned.  Otherwise, we return with a happy return value.  Of course, <tt>inflateEnd()</tt>
+is called first to avoid a memory leak.
+<pre><b>
+    /* clean up and return */
+    (void)inflateEnd(&amp;strm);
+    return ret == Z_STREAM_END ? Z_OK : Z_DATA_ERROR;
+}
+</b></pre><!-- -->
+That ends the routines that directly use <em>zlib</em>.  The following routines make this
+a command-line program by running data through the above routines from <tt>stdin</tt> to
+<tt>stdout</tt>, and handling any errors reported by <tt>def()</tt> or <tt>inf()</tt>.
+<p>
+<tt>zerr()</tt> is used to interpret the possible error codes from <tt>def()</tt>
+and <tt>inf()</tt>, as detailed in their comments above, and print out an error message.
+Note that these are only a subset of the possible return values from <tt>deflate()</tt>
+and <tt>inflate()</tt>.
+<pre><b>
+/* report a zlib or i/o error */
+void zerr(int ret)
+{
+    fputs("zpipe: ", stderr);
+    switch (ret) {
+    case Z_ERRNO:
+        if (ferror(stdin))
+            fputs("error reading stdin\n", stderr);
+        if (ferror(stdout))
+            fputs("error writing stdout\n", stderr);
+        break;
+    case Z_STREAM_ERROR:
+        fputs("invalid compression level\n", stderr);
+        break;
+    case Z_DATA_ERROR:
+        fputs("invalid or incomplete deflate data\n", stderr);
+        break;
+    case Z_MEM_ERROR:
+        fputs("out of memory\n", stderr);
+        break;
+    case Z_VERSION_ERROR:
+        fputs("zlib version mismatch!\n", stderr);
+    }
+}
+</b></pre><!-- -->
+Here is the <tt>main()</tt> routine used to test <tt>def()</tt> and <tt>inf()</tt>.  The
+<tt>zpipe</tt> command is simply a compression pipe from <tt>stdin</tt> to <tt>stdout</tt>, if
+no arguments are given, or it is a decompression pipe if <tt>zpipe -d</tt> is used.  If any other
+arguments are provided, no compression or decompression is performed.  Instead a usage
+message is displayed.  Examples are <tt>zpipe < foo.txt > foo.txt.z</tt> to compress, and
+<tt>zpipe -d < foo.txt.z > foo.txt</tt> to decompress.
+<pre><b>
+/* compress or decompress from stdin to stdout */
+int main(int argc, char **argv)
+{
+    int ret;
+
+    /* avoid end-of-line conversions */
+    SET_BINARY_MODE(stdin);
+    SET_BINARY_MODE(stdout);
+
+    /* do compression if no arguments */
+    if (argc == 1) {
+        ret = def(stdin, stdout, Z_DEFAULT_COMPRESSION);
+        if (ret != Z_OK)
+            zerr(ret);
+        return ret;
+    }
+
+    /* do decompression if -d specified */
+    else if (argc == 2 &amp;&amp; strcmp(argv[1], "-d") == 0) {
+        ret = inf(stdin, stdout);
+        if (ret != Z_OK)
+            zerr(ret);
+        return ret;
+    }
+
+    /* otherwise, report usage */
+    else {
+        fputs("zpipe usage: zpipe [-d] &lt; source &gt; dest\n", stderr);
+        return 1;
+    }
+}
+</b></pre>
+<hr>
+<i>Copyright (c) 2004, 2005 by Mark Adler<br>Last modified 11 December 2005</i>
+</body>
+</html>
diff --git a/zlib/examples/zpipe.c b/zlib/examples/zpipe.c
new file mode 100644
index 0000000..83535d1
--- /dev/null
+++ b/zlib/examples/zpipe.c
@@ -0,0 +1,205 @@
+/* zpipe.c: example of proper use of zlib's inflate() and deflate()
+   Not copyrighted -- provided to the public domain
+   Version 1.4  11 December 2005  Mark Adler */
+
+/* Version history:
+   1.0  30 Oct 2004  First version
+   1.1   8 Nov 2004  Add void casting for unused return values
+                     Use switch statement for inflate() return values
+   1.2   9 Nov 2004  Add assertions to document zlib guarantees
+   1.3   6 Apr 2005  Remove incorrect assertion in inf()
+   1.4  11 Dec 2005  Add hack to avoid MSDOS end-of-line conversions
+                     Avoid some compiler warnings for input and output buffers
+ */
+
+#include <stdio.h>
+#include <string.h>
+#include <assert.h>
+#include "zlib.h"
+
+#if defined(MSDOS) || defined(OS2) || defined(WIN32) || defined(__CYGWIN__)
+#  include <fcntl.h>
+#  include <io.h>
+#  define SET_BINARY_MODE(file) setmode(fileno(file), O_BINARY)
+#else
+#  define SET_BINARY_MODE(file)
+#endif
+
+#define CHUNK 16384
+
+/* Compress from file source to file dest until EOF on source.
+   def() returns Z_OK on success, Z_MEM_ERROR if memory could not be
+   allocated for processing, Z_STREAM_ERROR if an invalid compression
+   level is supplied, Z_VERSION_ERROR if the version of zlib.h and the
+   version of the library linked do not match, or Z_ERRNO if there is
+   an error reading or writing the files. */
+int def(FILE *source, FILE *dest, int level)
+{
+    int ret, flush;
+    unsigned have;
+    z_stream strm;
+    unsigned char in[CHUNK];
+    unsigned char out[CHUNK];
+
+    /* allocate deflate state */
+    strm.zalloc = Z_NULL;
+    strm.zfree = Z_NULL;
+    strm.opaque = Z_NULL;
+    ret = deflateInit(&strm, level);
+    if (ret != Z_OK)
+        return ret;
+
+    /* compress until end of file */
+    do {
+        strm.avail_in = fread(in, 1, CHUNK, source);
+        if (ferror(source)) {
+            (void)deflateEnd(&strm);
+            return Z_ERRNO;
+        }
+        flush = feof(source) ? Z_FINISH : Z_NO_FLUSH;
+        strm.next_in = in;
+
+        /* run deflate() on input until output buffer not full, finish
+           compression if all of source has been read in */
+        do {
+            strm.avail_out = CHUNK;
+            strm.next_out = out;
+            ret = deflate(&strm, flush);    /* no bad return value */
+            assert(ret != Z_STREAM_ERROR);  /* state not clobbered */
+            have = CHUNK - strm.avail_out;
+            if (fwrite(out, 1, have, dest) != have || ferror(dest)) {
+                (void)deflateEnd(&strm);
+                return Z_ERRNO;
+            }
+        } while (strm.avail_out == 0);
+        assert(strm.avail_in == 0);     /* all input will be used */
+
+        /* done when last data in file processed */
+    } while (flush != Z_FINISH);
+    assert(ret == Z_STREAM_END);        /* stream will be complete */
+
+    /* clean up and return */
+    (void)deflateEnd(&strm);
+    return Z_OK;
+}
+
+/* Decompress from file source to file dest until stream ends or EOF.
+   inf() returns Z_OK on success, Z_MEM_ERROR if memory could not be
+   allocated for processing, Z_DATA_ERROR if the deflate data is
+   invalid or incomplete, Z_VERSION_ERROR if the version of zlib.h and
+   the version of the library linked do not match, or Z_ERRNO if there
+   is an error reading or writing the files. */
+int inf(FILE *source, FILE *dest)
+{
+    int ret;
+    unsigned have;
+    z_stream strm;
+    unsigned char in[CHUNK];
+    unsigned char out[CHUNK];
+
+    /* allocate inflate state */
+    strm.zalloc = Z_NULL;
+    strm.zfree = Z_NULL;
+    strm.opaque = Z_NULL;
+    strm.avail_in = 0;
+    strm.next_in = Z_NULL;
+    ret = inflateInit(&strm);
+    if (ret != Z_OK)
+        return ret;
+
+    /* decompress until deflate stream ends or end of file */
+    do {
+        strm.avail_in = fread(in, 1, CHUNK, source);
+        if (ferror(source)) {
+            (void)inflateEnd(&strm);
+            return Z_ERRNO;
+        }
+        if (strm.avail_in == 0)
+            break;
+        strm.next_in = in;
+
+        /* run inflate() on input until output buffer not full */
+        do {
+            strm.avail_out = CHUNK;
+            strm.next_out = out;
+            ret = inflate(&strm, Z_NO_FLUSH);
+            assert(ret != Z_STREAM_ERROR);  /* state not clobbered */
+            switch (ret) {
+            case Z_NEED_DICT:
+                ret = Z_DATA_ERROR;     /* and fall through */
+            case Z_DATA_ERROR:
+            case Z_MEM_ERROR:
+                (void)inflateEnd(&strm);
+                return ret;
+            }
+            have = CHUNK - strm.avail_out;
+            if (fwrite(out, 1, have, dest) != have || ferror(dest)) {
+                (void)inflateEnd(&strm);
+                return Z_ERRNO;
+            }
+        } while (strm.avail_out == 0);
+
+        /* done when inflate() says it's done */
+    } while (ret != Z_STREAM_END);
+
+    /* clean up and return */
+    (void)inflateEnd(&strm);
+    return ret == Z_STREAM_END ? Z_OK : Z_DATA_ERROR;
+}
+
+/* report a zlib or i/o error */
+void zerr(int ret)
+{
+    fputs("zpipe: ", stderr);
+    switch (ret) {
+    case Z_ERRNO:
+        if (ferror(stdin))
+            fputs("error reading stdin\n", stderr);
+        if (ferror(stdout))
+            fputs("error writing stdout\n", stderr);
+        break;
+    case Z_STREAM_ERROR:
+        fputs("invalid compression level\n", stderr);
+        break;
+    case Z_DATA_ERROR:
+        fputs("invalid or incomplete deflate data\n", stderr);
+        break;
+    case Z_MEM_ERROR:
+        fputs("out of memory\n", stderr);
+        break;
+    case Z_VERSION_ERROR:
+        fputs("zlib version mismatch!\n", stderr);
+    }
+}
+
+/* compress or decompress from stdin to stdout */
+int main(int argc, char **argv)
+{
+    int ret;
+
+    /* avoid end-of-line conversions */
+    SET_BINARY_MODE(stdin);
+    SET_BINARY_MODE(stdout);
+
+    /* do compression if no arguments */
+    if (argc == 1) {
+        ret = def(stdin, stdout, Z_DEFAULT_COMPRESSION);
+        if (ret != Z_OK)
+            zerr(ret);
+        return ret;
+    }
+
+    /* do decompression if -d specified */
+    else if (argc == 2 && strcmp(argv[1], "-d") == 0) {
+        ret = inf(stdin, stdout);
+        if (ret != Z_OK)
+            zerr(ret);
+        return ret;
+    }
+
+    /* otherwise, report usage */
+    else {
+        fputs("zpipe usage: zpipe [-d] < source > dest\n", stderr);
+        return 1;
+    }
+}
diff --git a/zlib/examples/zran.c b/zlib/examples/zran.c
new file mode 100644
index 0000000..617a130
--- /dev/null
+++ b/zlib/examples/zran.c
@@ -0,0 +1,404 @@
+/* zran.c -- example of zlib/gzip stream indexing and random access
+ * Copyright (C) 2005 Mark Adler
+ * For conditions of distribution and use, see copyright notice in zlib.h
+   Version 1.0  29 May 2005  Mark Adler */
+
+/* Illustrate the use of Z_BLOCK, inflatePrime(), and inflateSetDictionary()
+   for random access of a compressed file.  A file containing a zlib or gzip
+   stream is provided on the command line.  The compressed stream is decoded in
+   its entirety, and an index built with access points about every SPAN bytes
+   in the uncompressed output.  The compressed file is left open, and can then
+   be read randomly, having to decompress on the average SPAN/2 uncompressed
+   bytes before getting to the desired block of data.
+
+   An access point can be created at the start of any deflate block, by saving
+   the starting file offset and bit of that block, and the 32K bytes of
+   uncompressed data that precede that block.  Also the uncompressed offset of
+   that block is saved to provide a referece for locating a desired starting
+   point in the uncompressed stream.  build_index() works by decompressing the
+   input zlib or gzip stream a block at a time, and at the end of each block
+   deciding if enough uncompressed data has gone by to justify the creation of
+   a new access point.  If so, that point is saved in a data structure that
+   grows as needed to accommodate the points.
+
+   To use the index, an offset in the uncompressed data is provided, for which
+   the latest accees point at or preceding that offset is located in the index.
+   The input file is positioned to the specified location in the index, and if
+   necessary the first few bits of the compressed data is read from the file.
+   inflate is initialized with those bits and the 32K of uncompressed data, and
+   the decompression then proceeds until the desired offset in the file is
+   reached.  Then the decompression continues to read the desired uncompressed
+   data from the file.
+
+   Another approach would be to generate the index on demand.  In that case,
+   requests for random access reads from the compressed data would try to use
+   the index, but if a read far enough past the end of the index is required,
+   then further index entries would be generated and added.
+
+   There is some fair bit of overhead to starting inflation for the random
+   access, mainly copying the 32K byte dictionary.  So if small pieces of the
+   file are being accessed, it would make sense to implement a cache to hold
+   some lookahead and avoid many calls to extract() for small lengths.
+
+   Another way to build an index would be to use inflateCopy().  That would
+   not be constrained to have access points at block boundaries, but requires
+   more memory per access point, and also cannot be saved to file due to the
+   use of pointers in the state.  The approach here allows for storage of the
+   index in a file.
+ */
+
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include "zlib.h"
+
+#define local static
+
+#define SPAN 1048576L       /* desired distance between access points */
+#define WINSIZE 32768U      /* sliding window size */
+#define CHUNK 16384         /* file input buffer size */
+
+/* access point entry */
+struct point {
+    off_t out;          /* corresponding offset in uncompressed data */
+    off_t in;           /* offset in input file of first full byte */
+    int bits;           /* number of bits (1-7) from byte at in - 1, or 0 */
+    unsigned char window[WINSIZE];  /* preceding 32K of uncompressed data */
+};
+
+/* access point list */
+struct access {
+    int have;           /* number of list entries filled in */
+    int size;           /* number of list entries allocated */
+    struct point *list; /* allocated list */
+};
+
+/* Deallocate an index built by build_index() */
+local void free_index(struct access *index)
+{
+    if (index != NULL) {
+        free(index->list);
+        free(index);
+    }
+}
+
+/* Add an entry to the access point list.  If out of memory, deallocate the
+   existing list and return NULL. */
+local struct access *addpoint(struct access *index, int bits,
+    off_t in, off_t out, unsigned left, unsigned char *window)
+{
+    struct point *next;
+
+    /* if list is empty, create it (start with eight points) */
+    if (index == NULL) {
+        index = malloc(sizeof(struct access));
+        if (index == NULL) return NULL;
+        index->list = malloc(sizeof(struct point) << 3);
+        if (index->list == NULL) {
+            free(index);
+            return NULL;
+        }
+        index->size = 8;
+        index->have = 0;
+    }
+
+    /* if list is full, make it bigger */
+    else if (index->have == index->size) {
+        index->size <<= 1;
+        next = realloc(index->list, sizeof(struct point) * index->size);
+        if (next == NULL) {
+            free_index(index);
+            return NULL;
+        }
+        index->list = next;
+    }
+
+    /* fill in entry and increment how many we have */
+    next = index->list + index->have;
+    next->bits = bits;
+    next->in = in;
+    next->out = out;
+    if (left)
+        memcpy(next->window, window + WINSIZE - left, left);
+    if (left < WINSIZE)
+        memcpy(next->window + left, window, WINSIZE - left);
+    index->have++;
+
+    /* return list, possibly reallocated */
+    return index;
+}
+
+/* Make one entire pass through the compressed stream and build an index, with
+   access points about every span bytes of uncompressed output -- span is
+   chosen to balance the speed of random access against the memory requirements
+   of the list, about 32K bytes per access point.  Note that data after the end
+   of the first zlib or gzip stream in the file is ignored.  build_index()
+   returns the number of access points on success (>= 1), Z_MEM_ERROR for out
+   of memory, Z_DATA_ERROR for an error in the input file, or Z_ERRNO for a
+   file read error.  On success, *built points to the resulting index. */
+local int build_index(FILE *in, off_t span, struct access **built)
+{
+    int ret;
+    off_t totin, totout;        /* our own total counters to avoid 4GB limit */
+    off_t last;                 /* totout value of last access point */
+    struct access *index;       /* access points being generated */
+    z_stream strm;
+    unsigned char input[CHUNK];
+    unsigned char window[WINSIZE];
+
+    /* initialize inflate */
+    strm.zalloc = Z_NULL;
+    strm.zfree = Z_NULL;
+    strm.opaque = Z_NULL;
+    strm.avail_in = 0;
+    strm.next_in = Z_NULL;
+    ret = inflateInit2(&strm, 47);      /* automatic zlib or gzip decoding */
+    if (ret != Z_OK)
+        return ret;
+
+    /* inflate the input, maintain a sliding window, and build an index -- this
+       also validates the integrity of the compressed data using the check
+       information at the end of the gzip or zlib stream */
+    totin = totout = last = 0;
+    index = NULL;               /* will be allocated by first addpoint() */
+    strm.avail_out = 0;
+    do {
+        /* get some compressed data from input file */
+        strm.avail_in = fread(input, 1, CHUNK, in);
+        if (ferror(in)) {
+            ret = Z_ERRNO;
+            goto build_index_error;
+        }
+        if (strm.avail_in == 0) {
+            ret = Z_DATA_ERROR;
+            goto build_index_error;
+        }
+        strm.next_in = input;
+
+        /* process all of that, or until end of stream */
+        do {
+            /* reset sliding window if necessary */
+            if (strm.avail_out == 0) {
+                strm.avail_out = WINSIZE;
+                strm.next_out = window;
+            }
+
+            /* inflate until out of input, output, or at end of block --
+               update the total input and output counters */
+            totin += strm.avail_in;
+            totout += strm.avail_out;
+            ret = inflate(&strm, Z_BLOCK);      /* return at end of block */
+            totin -= strm.avail_in;
+            totout -= strm.avail_out;
+            if (ret == Z_NEED_DICT)
+                ret = Z_DATA_ERROR;
+            if (ret == Z_MEM_ERROR || ret == Z_DATA_ERROR)
+                goto build_index_error;
+            if (ret == Z_STREAM_END)
+                break;
+
+            /* if at end of block, consider adding an index entry (note that if
+               data_type indicates an end-of-block, then all of the
+               uncompressed data from that block has been delivered, and none
+               of the compressed data after that block has been consumed,
+               except for up to seven bits) -- the totout == 0 provides an
+               entry point after the zlib or gzip header, and assures that the
+               index always has at least one access point; we avoid creating an
+               access point after the last block by checking bit 6 of data_type
+             */
+            if ((strm.data_type & 128) && !(strm.data_type & 64) &&
+                (totout == 0 || totout - last > span)) {
+                index = addpoint(index, strm.data_type & 7, totin,
+                                 totout, strm.avail_out, window);
+                if (index == NULL) {
+                    ret = Z_MEM_ERROR;
+                    goto build_index_error;
+                }
+                last = totout;
+            }
+        } while (strm.avail_in != 0);
+    } while (ret != Z_STREAM_END);
+
+    /* clean up and return index (release unused entries in list) */
+    (void)inflateEnd(&strm);
+    index = realloc(index, sizeof(struct point) * index->have);
+    index->size = index->have;
+    *built = index;
+    return index->size;
+
+    /* return error */
+  build_index_error:
+    (void)inflateEnd(&strm);
+    if (index != NULL)
+        free_index(index);
+    return ret;
+}
+
+/* Use the index to read len bytes from offset into buf, return bytes read or
+   negative for error (Z_DATA_ERROR or Z_MEM_ERROR).  If data is requested past
+   the end of the uncompressed data, then extract() will return a value less
+   than len, indicating how much as actually read into buf.  This function
+   should not return a data error unless the file was modified since the index
+   was generated.  extract() may also return Z_ERRNO if there is an error on
+   reading or seeking the input file. */
+local int extract(FILE *in, struct access *index, off_t offset,
+                  unsigned char *buf, int len)
+{
+    int ret, skip;
+    z_stream strm;
+    struct point *here;
+    unsigned char input[CHUNK];
+    unsigned char discard[WINSIZE];
+
+    /* proceed only if something reasonable to do */
+    if (len < 0)
+        return 0;
+
+    /* find where in stream to start */
+    here = index->list;
+    ret = index->have;
+    while (--ret && here[1].out <= offset)
+        here++;
+
+    /* initialize file and inflate state to start there */
+    strm.zalloc = Z_NULL;
+    strm.zfree = Z_NULL;
+    strm.opaque = Z_NULL;
+    strm.avail_in = 0;
+    strm.next_in = Z_NULL;
+    ret = inflateInit2(&strm, -15);         /* raw inflate */
+    if (ret != Z_OK)
+        return ret;
+    ret = fseeko(in, here->in - (here->bits ? 1 : 0), SEEK_SET);
+    if (ret == -1)
+        goto extract_ret;
+    if (here->bits) {
+        ret = getc(in);
+        if (ret == -1) {
+            ret = ferror(in) ? Z_ERRNO : Z_DATA_ERROR;
+            goto extract_ret;
+        }
+        (void)inflatePrime(&strm, here->bits, ret >> (8 - here->bits));
+    }
+    (void)inflateSetDictionary(&strm, here->window, WINSIZE);
+
+    /* skip uncompressed bytes until offset reached, then satisfy request */
+    offset -= here->out;
+    strm.avail_in = 0;
+    skip = 1;                               /* while skipping to offset */
+    do {
+        /* define where to put uncompressed data, and how much */
+        if (offset == 0 && skip) {          /* at offset now */
+            strm.avail_out = len;
+            strm.next_out = buf;
+            skip = 0;                       /* only do this once */
+        }
+        if (offset > WINSIZE) {             /* skip WINSIZE bytes */
+            strm.avail_out = WINSIZE;
+            strm.next_out = discard;
+            offset -= WINSIZE;
+        }
+        else if (offset != 0) {             /* last skip */
+            strm.avail_out = (unsigned)offset;
+            strm.next_out = discard;
+            offset = 0;
+        }
+
+        /* uncompress until avail_out filled, or end of stream */
+        do {
+            if (strm.avail_in == 0) {
+                strm.avail_in = fread(input, 1, CHUNK, in);
+                if (ferror(in)) {
+                    ret = Z_ERRNO;
+                    goto extract_ret;
+                }
+                if (strm.avail_in == 0) {
+                    ret = Z_DATA_ERROR;
+                    goto extract_ret;
+                }
+                strm.next_in = input;
+            }
+            ret = inflate(&strm, Z_NO_FLUSH);       /* normal inflate */
+            if (ret == Z_NEED_DICT)
+                ret = Z_DATA_ERROR;
+            if (ret == Z_MEM_ERROR || ret == Z_DATA_ERROR)
+                goto extract_ret;
+            if (ret == Z_STREAM_END)
+                break;
+        } while (strm.avail_out != 0);
+
+        /* if reach end of stream, then don't keep trying to get more */
+        if (ret == Z_STREAM_END)
+            break;
+
+        /* do until offset reached and requested data read, or stream ends */
+    } while (skip);
+
+    /* compute number of uncompressed bytes read after offset */
+    ret = skip ? 0 : len - strm.avail_out;
+
+    /* clean up and return bytes read or error */
+  extract_ret:
+    (void)inflateEnd(&strm);
+    return ret;
+}
+
+/* Demonstrate the use of build_index() and extract() by processing the file
+   provided on the command line, and the extracting 16K from about 2/3rds of
+   the way through the uncompressed output, and writing that to stdout. */
+int main(int argc, char **argv)
+{
+    int len;
+    off_t offset;
+    FILE *in;
+    struct access *index = NULL;
+    unsigned char buf[CHUNK];
+
+    /* open input file */
+    if (argc != 2) {
+        fprintf(stderr, "usage: zran file.gz\n");
+        return 1;
+    }
+    in = fopen(argv[1], "rb");
+    if (in == NULL) {
+        fprintf(stderr, "zran: could not open %s for reading\n", argv[1]);
+        return 1;
+    }
+
+    /* build index */
+    len = build_index(in, SPAN, &index);
+    if (len < 0) {
+        fclose(in);
+        switch (len) {
+        case Z_MEM_ERROR:
+            fprintf(stderr, "zran: out of memory\n");
+            break;
+        case Z_DATA_ERROR:
+            fprintf(stderr, "zran: compressed data error in %s\n", argv[1]);
+            break;
+        case Z_ERRNO:
+            fprintf(stderr, "zran: read error on %s\n", argv[1]);
+            break;
+        default:
+            fprintf(stderr, "zran: error %d while building index\n", len);
+        }
+        return 1;
+    }
+    fprintf(stderr, "zran: built index with %d access points\n", len);
+
+    /* use index by reading some bytes from an arbitrary offset */
+    offset = (index->list[index->have - 1].out << 1) / 3;
+    len = extract(in, index, offset, buf, CHUNK);
+    if (len < 0)
+        fprintf(stderr, "zran: extraction failed: %s error\n",
+                len == Z_MEM_ERROR ? "out of memory" : "input corrupted");
+    else {
+        fwrite(buf, 1, len, stdout);
+        fprintf(stderr, "zran: extracted %d bytes at %llu\n", len, offset);
+    }
+
+    /* clean up and exit */
+    free_index(index);
+    fclose(in);
+    return 0;
+}