gl/strstr.c

   1 /* Copyright (C) 1991, 1992, 1993, 1994, 1996, 1997, 1998, 2000, 2004, 2007,
   2    2008, 2009, 2010 Free Software Foundation, Inc.
   3    This file is part of the GNU C Library.
   4
   5    This program is free software; you can redistribute it and/or modify
   6    it under the terms of the GNU General Public License as published by
   7    the Free Software Foundation; either version 3, or (at your option)
   8    any later version.
   9
  10    This program is distributed in the hope that it will be useful,
  11    but WITHOUT ANY WARRANTY; without even the implied warranty of
  12    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  13    GNU General Public License for more details.
  14
  15    You should have received a copy of the GNU General Public License along
  16    with this program; if not, write to the Free Software Foundation,
  17    Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.  */
  18
  19 /* This particular implementation was written by Eric Blake, 2008.  */
  20
  21 #ifndef _LIBC
  22 # include <config.h>
  23 #endif
  24
  25 /* Specification of strstr.  */
  26 #include <string.h>
  27
  28 #include <stdbool.h>
  29
  30 #ifndef _LIBC
  31 # define __builtin_expect(expr, val)   (expr)
  32 #endif
  33
  34 #define RETURN_TYPE char *
  35 #define AVAILABLE(h, h_l, j, n_l)                       \
  36   (!memchr ((h) + (h_l), '\0', (j) + (n_l) - (h_l))     \
  37    && ((h_l) = (j) + (n_l)))
  38 #include "str-two-way.h"
  39
  40 /* Return the first occurrence of NEEDLE in HAYSTACK.  Return HAYSTACK
  41    if NEEDLE is empty, otherwise NULL if NEEDLE is not found in
  42    HAYSTACK.  */
  43 char *
  44 strstr (const char *haystack_start, const char *needle_start)
  45 {
  46   const char *haystack = haystack_start;
  47   const char *needle = needle_start;
  48   size_t needle_len; /* Length of NEEDLE.  */
  49   size_t haystack_len; /* Known minimum length of HAYSTACK.  */
  50   bool ok = true; /* True if NEEDLE is prefix of HAYSTACK.  */
  51
  52   /* Determine length of NEEDLE, and in the process, make sure
  53      HAYSTACK is at least as long (no point processing all of a long
  54      NEEDLE if HAYSTACK is too short).  */
  55   while (*haystack && *needle)
  56     ok &= *haystack++ == *needle++;
  57   if (*needle)
  58     return NULL;
  59   if (ok)
  60     return (char *) haystack_start;
  61
  62   /* Reduce the size of haystack using strchr, since it has a smaller
  63      linear coefficient than the Two-Way algorithm.  */
  64   needle_len = needle - needle_start;
  65   haystack = strchr (haystack_start + 1, *needle_start);
  66   if (!haystack || __builtin_expect (needle_len == 1, 0))
  67     return (char *) haystack;
  68   needle -= needle_len;
  69   haystack_len = (haystack > haystack_start + needle_len ? 1
  70                   : needle_len + haystack_start - haystack);
  71
  72   /* Perform the search.  Abstract memory is considered to be an array
  73      of 'unsigned char' values, not an array of 'char' values.  See
  74      ISO C 99 section 6.2.6.1.  */
  75   if (needle_len < LONG_NEEDLE_THRESHOLD)
  76     return two_way_short_needle ((const unsigned char *) haystack,
  77                                  haystack_len,
  78                                  (const unsigned char *) needle, needle_len);
  79   return two_way_long_needle ((const unsigned char *) haystack, haystack_len,
  80                               (const unsigned char *) needle, needle_len);
  81 }
  82
  83 #undef LONG_NEEDLE_THRESHOLD