string/strstr.c

   1 /* Return the offset of one string within another.
   2    Copyright (C) 1994,1996,1997,2000,2001,2003,2008 Free Software Foundation, Inc.
   3    This file is part of the GNU C Library.
   4
   5    The GNU C Library is free software; you can redistribute it and/or
   6    modify it under the terms of the GNU Lesser General Public
   7    License as published by the Free Software Foundation; either
   8    version 2.1 of the License, or (at your option) any later version.
   9
  10    The GNU C Library 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 GNU
  13    Lesser General Public License for more details.
  14
  15    You should have received a copy of the GNU Lesser General Public
  16    License along with the GNU C Library; if not, write to the Free
  17    Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA
  18    02111-1307 USA.  */
  19
  20 /* This particular implementation was written by Eric Blake, 2008.  */
  21
  22 #ifndef _LIBC
  23 # include <config.h>
  24 #endif
  25
  26 /* Specification of strstr.  */
  27 #include <string.h>
  28
  29 #include <stdbool.h>
  30
  31 #ifndef _LIBC
  32 # define __builtin_expect(expr, val)   (expr)
  33 #endif
  34
  35 #define RETURN_TYPE char *
  36 #define AVAILABLE(h, h_l, j, n_l)                       \
  37   (!memchr ((h) + (h_l), '\0', (j) + (n_l) - (h_l))     \
  38    && ((h_l) = (j) + (n_l)))
  39 #include "str-two-way.h"
  40
  41 #undef strstr
  42
  43 /* Return the first occurrence of NEEDLE in HAYSTACK.  Return HAYSTACK
  44    if NEEDLE is empty, otherwise NULL if NEEDLE is not found in
  45    HAYSTACK.  */
  46 char *
  47 strstr (const char *haystack_start, const char *needle_start)
  48 {
  49   const char *haystack = haystack_start;
  50   const char *needle = needle_start;
  51   size_t needle_len; /* Length of NEEDLE.  */
  52   size_t haystack_len; /* Known minimum length of HAYSTACK.  */
  53   bool ok = true; /* True if NEEDLE is prefix of HAYSTACK.  */
  54
  55   /* Determine length of NEEDLE, and in the process, make sure
  56      HAYSTACK is at least as long (no point processing all of a long
  57      NEEDLE if HAYSTACK is too short).  */
  58   while (*haystack && *needle)
  59     ok &= *haystack++ == *needle++;
  60   if (*needle)
  61     return NULL;
  62   if (ok)
  63     return (char *) haystack_start;
  64
  65   /* Reduce the size of haystack using strchr, since it has a smaller
  66      linear coefficient than the Two-Way algorithm.  */
  67   needle_len = needle - needle_start;
  68   haystack = strchr (haystack_start + 1, *needle_start);
  69   if (!haystack || __builtin_expect (needle_len == 1, 0))
  70     return (char *) haystack;
  71   needle -= needle_len;
  72   haystack_len = (haystack > haystack_start + needle_len ? 1
  73                   : needle_len + haystack_start - haystack);
  74
  75   /* Perform the search.  Abstract memory is considered to be an array
  76      of 'unsigned char' values, not an array of 'char' values.  See
  77      ISO C 99 section 6.2.6.1.  */
  78   if (needle_len < LONG_NEEDLE_THRESHOLD)
  79     return two_way_short_needle ((const unsigned char *) haystack,
  80                                  haystack_len,
  81                                  (const unsigned char *) needle, needle_len);
  82   return two_way_long_needle ((const unsigned char *) haystack, haystack_len,
  83                               (const unsigned char *) needle, needle_len);
  84 }
  85 libc_hidden_builtin_def (strstr)
  86
  87 #undef LONG_NEEDLE_THRESHOLD