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+
+                Frequently Asked Questions about zlib
+
+
+If your question is not there, please check the zlib home page
+http://zlib.net/ which may have more recent information.
+The lastest zlib FAQ is at http://zlib.net/zlib_faq.html
+
+
+ 1. Is zlib Y2K-compliant?
+
+    Yes. zlib doesn't handle dates.
+
+ 2. Where can I get a Windows DLL version?
+
+    The zlib sources can be compiled without change to produce a DLL.  See the
+    file win32/DLL_FAQ.txt in the zlib distribution.  Pointers to the
+    precompiled DLL are found in the zlib web site at http://zlib.net/ .
+
+ 3. Where can I get a Visual Basic interface to zlib?
+
+    See
+        * http://marknelson.us/1997/01/01/zlib-engine/
+        * win32/DLL_FAQ.txt in the zlib distribution
+
+ 4. compress() returns Z_BUF_ERROR.
+
+    Make sure that before the call of compress(), the length of the compressed
+    buffer is equal to the available size of the compressed buffer and not
+    zero.  For Visual Basic, check that this parameter is passed by reference
+    ("as any"), not by value ("as long").
+
+ 5. deflate() or inflate() returns Z_BUF_ERROR.
+
+    Before making the call, make sure that avail_in and avail_out are not zero.
+    When setting the parameter flush equal to Z_FINISH, also make sure that
+    avail_out is big enough to allow processing all pending input.  Note that a
+    Z_BUF_ERROR is not fatal--another call to deflate() or inflate() can be
+    made with more input or output space.  A Z_BUF_ERROR may in fact be
+    unavoidable depending on how the functions are used, since it is not
+    possible to tell whether or not there is more output pending when
+    strm.avail_out returns with zero.  See http://zlib.net/zlib_how.html for a
+    heavily annotated example.
+
+ 6. Where's the zlib documentation (man pages, etc.)?
+
+    It's in zlib.h .  Examples of zlib usage are in the files test/example.c
+    and test/minigzip.c, with more in examples/ .
+
+ 7. Why don't you use GNU autoconf or libtool or ...?
+
+    Because we would like to keep zlib as a very small and simple package.
+    zlib is rather portable and doesn't need much configuration.
+
+ 8. I found a bug in zlib.
+
+    Most of the time, such problems are due to an incorrect usage of zlib.
+    Please try to reproduce the problem with a small program and send the
+    corresponding source to us at zlib@gzip.org .  Do not send multi-megabyte
+    data files without prior agreement.
+
+ 9. Why do I get "undefined reference to gzputc"?
+
+    If "make test" produces something like
+
+       example.o(.text+0x154): undefined reference to `gzputc'
+
+    check that you don't have old files libz.* in /usr/lib, /usr/local/lib or
+    /usr/X11R6/lib. Remove any old versions, then do "make install".
+
+10. I need a Delphi interface to zlib.
+
+    See the contrib/delphi directory in the zlib distribution.
+
+11. Can zlib handle .zip archives?
+
+    Not by itself, no.  See the directory contrib/minizip in the zlib
+    distribution.
+
+12. Can zlib handle .Z files?
+
+    No, sorry.  You have to spawn an uncompress or gunzip subprocess, or adapt
+    the code of uncompress on your own.
+
+13. How can I make a Unix shared library?
+
+    By default a shared (and a static) library is built for Unix.  So:
+
+    make distclean
+    ./configure
+    make
+
+14. How do I install a shared zlib library on Unix?
+
+    After the above, then:
+
+    make install
+
+    However, many flavors of Unix come with a shared zlib already installed.
+    Before going to the trouble of compiling a shared version of zlib and
+    trying to install it, you may want to check if it's already there!  If you
+    can #include <zlib.h>, it's there.  The -lz option will probably link to
+    it.  You can check the version at the top of zlib.h or with the
+    ZLIB_VERSION symbol defined in zlib.h .
+
+15. I have a question about OttoPDF.
+
+    We are not the authors of OttoPDF. The real author is on the OttoPDF web
+    site: Joel Hainley, jhainley@myndkryme.com.
+
+16. Can zlib decode Flate data in an Adobe PDF file?
+
+    Yes. See http://www.pdflib.com/ . To modify PDF forms, see
+    http://sourceforge.net/projects/acroformtool/ .
+
+17. Why am I getting this "register_frame_info not found" error on Solaris?
+
+    After installing zlib 1.1.4 on Solaris 2.6, running applications using zlib
+    generates an error such as:
+
+        ld.so.1: rpm: fatal: relocation error: file /usr/local/lib/libz.so:
+        symbol __register_frame_info: referenced symbol not found
+
+    The symbol __register_frame_info is not part of zlib, it is generated by
+    the C compiler (cc or gcc).  You must recompile applications using zlib
+    which have this problem.  This problem is specific to Solaris.  See
+    http://www.sunfreeware.com for Solaris versions of zlib and applications
+    using zlib.
+
+18. Why does gzip give an error on a file I make with compress/deflate?
+
+    The compress and deflate functions produce data in the zlib format, which
+    is different and incompatible with the gzip format.  The gz* functions in
+    zlib on the other hand use the gzip format.  Both the zlib and gzip formats
+    use the same compressed data format internally, but have different headers
+    and trailers around the compressed data.
+
+19. Ok, so why are there two different formats?
+
+    The gzip format was designed to retain the directory information about a
+    single file, such as the name and last modification date.  The zlib format
+    on the other hand was designed for in-memory and communication channel
+    applications, and has a much more compact header and trailer and uses a
+    faster integrity check than gzip.
+
+20. Well that's nice, but how do I make a gzip file in memory?
+
+    You can request that deflate write the gzip format instead of the zlib
+    format using deflateInit2().  You can also request that inflate decode the
+    gzip format using inflateInit2().  Read zlib.h for more details.
+
+21. Is zlib thread-safe?
+
+    Yes.  However any library routines that zlib uses and any application-
+    provided memory allocation routines must also be thread-safe.  zlib's gz*
+    functions use stdio library routines, and most of zlib's functions use the
+    library memory allocation routines by default.  zlib's *Init* functions
+    allow for the application to provide custom memory allocation routines.
+
+    Of course, you should only operate on any given zlib or gzip stream from a
+    single thread at a time.
+
+22. Can I use zlib in my commercial application?
+
+    Yes.  Please read the license in zlib.h.
+
+23. Is zlib under the GNU license?
+
+    No.  Please read the license in zlib.h.
+
+24. The license says that altered source versions must be "plainly marked". So
+    what exactly do I need to do to meet that requirement?
+
+    You need to change the ZLIB_VERSION and ZLIB_VERNUM #defines in zlib.h.  In
+    particular, the final version number needs to be changed to "f", and an
+    identification string should be appended to ZLIB_VERSION.  Version numbers
+    x.x.x.f are reserved for modifications to zlib by others than the zlib
+    maintainers.  For example, if the version of the base zlib you are altering
+    is "1.2.3.4", then in zlib.h you should change ZLIB_VERNUM to 0x123f, and
+    ZLIB_VERSION to something like "1.2.3.f-zachary-mods-v3".  You can also
+    update the version strings in deflate.c and inftrees.c.
+
+    For altered source distributions, you should also note the origin and
+    nature of the changes in zlib.h, as well as in ChangeLog and README, along
+    with the dates of the alterations.  The origin should include at least your
+    name (or your company's name), and an email address to contact for help or
+    issues with the library.
+
+    Note that distributing a compiled zlib library along with zlib.h and
+    zconf.h is also a source distribution, and so you should change
+    ZLIB_VERSION and ZLIB_VERNUM and note the origin and nature of the changes
+    in zlib.h as you would for a full source distribution.
+
+25. Will zlib work on a big-endian or little-endian architecture, and can I
+    exchange compressed data between them?
+
+    Yes and yes.
+
+26. Will zlib work on a 64-bit machine?
+
+    Yes.  It has been tested on 64-bit machines, and has no dependence on any
+    data types being limited to 32-bits in length.  If you have any
+    difficulties, please provide a complete problem report to zlib@gzip.org
+
+27. Will zlib decompress data from the PKWare Data Compression Library?
+
+    No.  The PKWare DCL uses a completely different compressed data format than
+    does PKZIP and zlib.  However, you can look in zlib's contrib/blast
+    directory for a possible solution to your problem.
+
+28. Can I access data randomly in a compressed stream?
+
+    No, not without some preparation.  If when compressing you periodically use
+    Z_FULL_FLUSH, carefully write all the pending data at those points, and
+    keep an index of those locations, then you can start decompression at those
+    points.  You have to be careful to not use Z_FULL_FLUSH too often, since it
+    can significantly degrade compression.  Alternatively, you can scan a
+    deflate stream once to generate an index, and then use that index for
+    random access.  See examples/zran.c .
+
+29. Does zlib work on MVS, OS/390, CICS, etc.?
+
+    It has in the past, but we have not heard of any recent evidence.  There
+    were working ports of zlib 1.1.4 to MVS, but those links no longer work.
+    If you know of recent, successful applications of zlib on these operating
+    systems, please let us know.  Thanks.
+
+30. Is there some simpler, easier to read version of inflate I can look at to
+    understand the deflate format?
+
+    First off, you should read RFC 1951.  Second, yes.  Look in zlib's
+    contrib/puff directory.
+
+31. Does zlib infringe on any patents?
+
+    As far as we know, no.  In fact, that was originally the whole point behind
+    zlib.  Look here for some more information:
+
+    http://www.gzip.org/#faq11
+
+32. Can zlib work with greater than 4 GB of data?
+
+    Yes.  inflate() and deflate() will process any amount of data correctly.
+    Each call of inflate() or deflate() is limited to input and output chunks
+    of the maximum value that can be stored in the compiler's "unsigned int"
+    type, but there is no limit to the number of chunks.  Note however that the
+    strm.total_in and strm_total_out counters may be limited to 4 GB.  These
+    counters are provided as a convenience and are not used internally by
+    inflate() or deflate().  The application can easily set up its own counters
+    updated after each call of inflate() or deflate() to count beyond 4 GB.
+    compress() and uncompress() may be limited to 4 GB, since they operate in a
+    single call.  gzseek() and gztell() may be limited to 4 GB depending on how
+    zlib is compiled.  See the zlibCompileFlags() function in zlib.h.
+
+    The word "may" appears several times above since there is a 4 GB limit only
+    if the compiler's "long" type is 32 bits.  If the compiler's "long" type is
+    64 bits, then the limit is 16 exabytes.
+
+33. Does zlib have any security vulnerabilities?
+
+    The only one that we are aware of is potentially in gzprintf().  If zlib is
+    compiled to use sprintf() or vsprintf(), then there is no protection
+    against a buffer overflow of an 8K string space (or other value as set by
+    gzbuffer()), other than the caller of gzprintf() assuring that the output
+    will not exceed 8K.  On the other hand, if zlib is compiled to use
+    snprintf() or vsnprintf(), which should normally be the case, then there is
+    no vulnerability.  The ./configure script will display warnings if an
+    insecure variation of sprintf() will be used by gzprintf().  Also the
+    zlibCompileFlags() function will return information on what variant of
+    sprintf() is used by gzprintf().
+
+    If you don't have snprintf() or vsnprintf() and would like one, you can
+    find a portable implementation here:
+
+        http://www.ijs.si/software/snprintf/
+
+    Note that you should be using the most recent version of zlib.  Versions
+    1.1.3 and before were subject to a double-free vulnerability, and versions
+    1.2.1 and 1.2.2 were subject to an access exception when decompressing
+    invalid compressed data.
+
+34. Is there a Java version of zlib?
+
+    Probably what you want is to use zlib in Java. zlib is already included
+    as part of the Java SDK in the java.util.zip package. If you really want
+    a version of zlib written in the Java language, look on the zlib home
+    page for links: http://zlib.net/ .
+
+35. I get this or that compiler or source-code scanner warning when I crank it
+    up to maximally-pedantic. Can't you guys write proper code?
+
+    Many years ago, we gave up attempting to avoid warnings on every compiler
+    in the universe.  It just got to be a waste of time, and some compilers
+    were downright silly as well as contradicted each other.  So now, we simply
+    make sure that the code always works.
+
+36. Valgrind (or some similar memory access checker) says that deflate is
+    performing a conditional jump that depends on an uninitialized value.
+    Isn't that a bug?
+
+    No.  That is intentional for performance reasons, and the output of deflate
+    is not affected.  This only started showing up recently since zlib 1.2.x
+    uses malloc() by default for allocations, whereas earlier versions used
+    calloc(), which zeros out the allocated memory.  Even though the code was
+    correct, versions 1.2.4 and later was changed to not stimulate these
+    checkers.
+
+37. Will zlib read the (insert any ancient or arcane format here) compressed
+    data format?
+
+    Probably not. Look in the comp.compression FAQ for pointers to various
+    formats and associated software.
+
+38. How can I encrypt/decrypt zip files with zlib?
+
+    zlib doesn't support encryption.  The original PKZIP encryption is very
+    weak and can be broken with freely available programs.  To get strong
+    encryption, use GnuPG, http://www.gnupg.org/ , which already includes zlib
+    compression.  For PKZIP compatible "encryption", look at
+    http://www.info-zip.org/
+
+39. What's the difference between the "gzip" and "deflate" HTTP 1.1 encodings?
+
+    "gzip" is the gzip format, and "deflate" is the zlib format.  They should
+    probably have called the second one "zlib" instead to avoid confusion with
+    the raw deflate compressed data format.  While the HTTP 1.1 RFC 2616
+    correctly points to the zlib specification in RFC 1950 for the "deflate"
+    transfer encoding, there have been reports of servers and browsers that
+    incorrectly produce or expect raw deflate data per the deflate
+    specification in RFC 1951, most notably Microsoft.  So even though the
+    "deflate" transfer encoding using the zlib format would be the more
+    efficient approach (and in fact exactly what the zlib format was designed
+    for), using the "gzip" transfer encoding is probably more reliable due to
+    an unfortunate choice of name on the part of the HTTP 1.1 authors.
+
+    Bottom line: use the gzip format for HTTP 1.1 encoding.
+
+40. Does zlib support the new "Deflate64" format introduced by PKWare?
+
+    No.  PKWare has apparently decided to keep that format proprietary, since
+    they have not documented it as they have previous compression formats.  In
+    any case, the compression improvements are so modest compared to other more
+    modern approaches, that it's not worth the effort to implement.
+
+41. I'm having a problem with the zip functions in zlib, can you help?
+
+    There are no zip functions in zlib.  You are probably using minizip by
+    Giles Vollant, which is found in the contrib directory of zlib.  It is not
+    part of zlib.  In fact none of the stuff in contrib is part of zlib.  The
+    files in there are not supported by the zlib authors.  You need to contact
+    the authors of the respective contribution for help.
+
+42. The match.asm code in contrib is under the GNU General Public License.
+    Since it's part of zlib, doesn't that mean that all of zlib falls under the
+    GNU GPL?
+
+    No.  The files in contrib are not part of zlib.  They were contributed by
+    other authors and are provided as a convenience to the user within the zlib
+    distribution.  Each item in contrib has its own license.
+
+43. Is zlib subject to export controls?  What is its ECCN?
+
+    zlib is not subject to export controls, and so is classified as EAR99.
+
+44. Can you please sign these lengthy legal documents and fax them back to us
+    so that we can use your software in our product?
+
+    No. Go away. Shoo.