string/memmem.c

   1 /* Copyright (C) 1991,92,93,94,96,97,98,2000,2004 Free Software Foundation, Inc.
   2    This file is part of the GNU C Library.
   3
   4    The GNU C Library is free software; you can redistribute it and/or
   5    modify it under the terms of the GNU Lesser General Public
   6    License as published by the Free Software Foundation; either
   7    version 2.1 of the License, or (at your option) any later version.
   8
   9    The GNU C Library is distributed in the hope that it will be useful,
  10    but WITHOUT ANY WARRANTY; without even the implied warranty of
  11    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  12    Lesser General Public License for more details.
  13
  14    You should have received a copy of the GNU Lesser General Public
  15    License along with the GNU C Library; if not, write to the Free
  16    Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA
  17    02111-1307 USA.  */
  18
  19 #include <stddef.h>
  20 #include <string.h>
  21
  22 #ifndef _LIBC
  23 # define __builtin_expect(expr, val)   (expr)
  24 #endif
  25
  26 #undef memmem
  27
  28 /* Return the first occurrence of NEEDLE in HAYSTACK.  */
  29 void *
  30 memmem (haystack, haystack_len, needle, needle_len)
  31      const void *haystack;
  32      size_t haystack_len;
  33      const void *needle;
  34      size_t needle_len;
  35 {
  36   const char *begin;
  37   const char *const last_possible
  38     = (const char *) haystack + haystack_len - needle_len;
  39
  40   if (needle_len == 0)
  41     /* The first occurrence of the empty string is deemed to occur at
  42        the beginning of the string.  */
  43     return (void *) haystack;
  44
  45   /* Sanity check, otherwise the loop might search through the whole
  46      memory.  */
  47   if (__builtin_expect (haystack_len < needle_len, 0))
  48     return NULL;
  49
  50   for (begin = (const char *) haystack; begin <= last_possible; ++begin)
  51     if (begin[0] == ((const char *) needle)[0] &&
  52         !memcmp ((const void *) &begin[1],
  53                  (const void *) ((const char *) needle + 1),
  54                  needle_len - 1))
  55       return (void *) begin;
  56
  57   return NULL;
  58 }