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authorUlrich Drepper <drepper@redhat.com>2008-05-15 04:42:20 +0000
committerUlrich Drepper <drepper@redhat.com>2008-05-15 04:42:20 +0000
commit0caca71ac95d12c6f45bbbe39d9adb7ac7074146 (patch)
tree5cf5eff46b5e4c7a09cebaf262bfcf3a20a0f6a1 /string/strstr.c
parentb194db79852e6bbd5d5ad72690679c8be06eef15 (diff)
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* string/Makefile (distribute): Add str-two-way.h.cvs/fedora-glibc-20080515T0735
2008-03-29 Eric Blake <ebb9@byu.net> Rewrite string searches to O(n) rather than O(n^2). * string/str-two-way.h: New file. For linear fixed-allocation string searching. * string/memmem.c: New implementation. * string/strstr.c: New implementation. * string/strcasestr.c: New implementation. * sysdeps/posix/getaddrinfo.c (getaddrinfo): Call _res_hconf_init
Diffstat (limited to 'string/strstr.c')
-rw-r--r--string/strstr.c142
1 files changed, 53 insertions, 89 deletions
diff --git a/string/strstr.c b/string/strstr.c
index fce1f2a..a9dc312 100644
--- a/string/strstr.c
+++ b/string/strstr.c
@@ -1,5 +1,5 @@
/* Return the offset of one string within another.
- Copyright (C) 1994,1996,1997,2000,2001,2003 Free Software Foundation, Inc.
+ Copyright (C) 1994,1996,1997,2000,2001,2003,2008 Free Software Foundation, Inc.
This file is part of the GNU C Library.
The GNU C Library is free software; you can redistribute it and/or
@@ -17,107 +17,71 @@
Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA
02111-1307 USA. */
-/*
- * My personal strstr() implementation that beats most other algorithms.
- * Until someone tells me otherwise, I assume that this is the
- * fastest implementation of strstr() in C.
- * I deliberately chose not to comment it. You should have at least
- * as much fun trying to understand it, as I had to write it :-).
- *
- * Stephen R. van den Berg, berg@pool.informatik.rwth-aachen.de */
+/* This particular implementation was written by Eric Blake, 2008. */
-#if HAVE_CONFIG_H
+#ifndef _LIBC
# include <config.h>
#endif
-#if defined _LIBC || defined HAVE_STRING_H
-# include <string.h>
+/* Specification of strstr. */
+#include <string.h>
+
+#include <stdbool.h>
+
+#ifndef _LIBC
+# define __builtin_expect(expr, val) (expr)
#endif
-typedef unsigned chartype;
+#define RETURN_TYPE char *
+#define AVAILABLE(h, h_l, j, n_l) \
+ (!memchr ((h) + (h_l), '\0', (j) + (n_l) - (h_l)) \
+ && ((h_l) = (j) + (n_l)))
+#include "str-two-way.h"
#undef strstr
+/* Return the first occurrence of NEEDLE in HAYSTACK. Return HAYSTACK
+ if NEEDLE is empty, otherwise NULL if NEEDLE is not found in
+ HAYSTACK. */
char *
-strstr (phaystack, pneedle)
- const char *phaystack;
- const char *pneedle;
+strstr (const char *haystack_start, const char *needle_start)
{
- const unsigned char *haystack, *needle;
- chartype b;
- const unsigned char *rneedle;
-
- haystack = (const unsigned char *) phaystack;
+ const char *haystack = haystack_start;
+ const char *needle = needle_start;
+ size_t needle_len; /* Length of NEEDLE. */
+ size_t haystack_len; /* Known minimum length of HAYSTACK. */
+ bool ok = true; /* True if NEEDLE is prefix of HAYSTACK. */
- if ((b = *(needle = (const unsigned char *) pneedle)))
- {
- chartype c;
- haystack--; /* possible ANSI violation */
+ /* Determine length of NEEDLE, and in the process, make sure
+ HAYSTACK is at least as long (no point processing all of a long
+ NEEDLE if HAYSTACK is too short). */
+ while (*haystack && *needle)
+ ok &= *haystack++ == *needle++;
+ if (*needle)
+ return NULL;
+ if (ok)
+ return (char *) haystack_start;
- {
- chartype a;
- do
- if (!(a = *++haystack))
- goto ret0;
- while (a != b);
- }
+ /* Reduce the size of haystack using strchr, since it has a smaller
+ linear coefficient than the Two-Way algorithm. */
+ needle_len = needle - needle_start;
+ haystack = strchr (haystack_start + 1, *needle_start);
+ if (!haystack || __builtin_expect (needle_len == 1, 0))
+ return (char *) haystack;
+ needle -= needle_len;
+ haystack_len = (haystack > haystack_start + needle_len ? 1
+ : needle_len + haystack_start - haystack);
- if (!(c = *++needle))
- goto foundneedle;
- ++needle;
- goto jin;
-
- for (;;)
- {
- {
- chartype a;
- if (0)
- jin:{
- if ((a = *++haystack) == c)
- goto crest;
- }
- else
- a = *++haystack;
- do
- {
- for (; a != b; a = *++haystack)
- {
- if (!a)
- goto ret0;
- if ((a = *++haystack) == b)
- break;
- if (!a)
- goto ret0;
- }
- }
- while ((a = *++haystack) != c);
- }
- crest:
- {
- chartype a;
- {
- const unsigned char *rhaystack;
- if (*(rhaystack = haystack-- + 1) == (a = *(rneedle = needle)))
- do
- {
- if (!a)
- goto foundneedle;
- if (*++rhaystack != (a = *++needle))
- break;
- if (!a)
- goto foundneedle;
- }
- while (*++rhaystack == (a = *++needle));
- needle = rneedle; /* took the register-poor aproach */
- }
- if (!a)
- break;
- }
- }
- }
-foundneedle:
- return (char *) haystack;
-ret0:
- return 0;
+ /* Perform the search. Abstract memory is considered to be an array
+ of 'unsigned char' values, not an array of 'char' values. See
+ ISO C 99 section 6.2.6.1. */
+ if (needle_len < LONG_NEEDLE_THRESHOLD)
+ return two_way_short_needle ((const unsigned char *) haystack,
+ haystack_len,
+ (const unsigned char *) needle, needle_len);
+ return two_way_long_needle ((const unsigned char *) haystack, haystack_len,
+ (const unsigned char *) needle, needle_len);
}
libc_hidden_builtin_def (strstr)
+
+#undef LONG_NEEDLE_THRESHOLD