sysdeps/generic/memmem.c

   1 /* Copyright (C) 1991,92,93,94,96,97,98,2000 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 #undef memmem
  23
  24 /* Return the first occurrence of NEEDLE in HAYSTACK.  */
  25 void *
  26 memmem (haystack, haystack_len, needle, needle_len)
  27      const void *haystack;
  28      size_t haystack_len;
  29      const void *needle;
  30      size_t needle_len;
  31 {
  32   const char *begin;
  33   const char *const last_possible
  34     = (const char *) haystack + haystack_len - needle_len;
  35
  36   if (needle_len == 0)
  37     /* The first occurrence of the empty string is deemed to occur at
  38        the beginning of the string.  */
  39     return (void *) haystack;
  40
  41   /* Sanity check, otherwise the loop might search through the whole
  42      memory.  */
  43   if (__builtin_expect (haystack_len < needle_len, 0))
  44     return NULL;
  45
  46   for (begin = (const char *) haystack; begin <= last_possible; ++begin)
  47     if (begin[0] == ((const char *) needle)[0] &&
  48         !memcmp ((const void *) &begin[1],
  49                  (const void *) ((const char *) needle + 1),
  50                  needle_len - 1))
  51       return (void *) begin;
  52
  53   return NULL;
  54 }