libiberty/memmem.c

   1 /* Copyright (C) 1991-2023 Free Software Foundation, Inc.
   2    This file is part of the GNU C Library.
   3
   4    This program is free software; you can redistribute it and/or modify
   5    it under the terms of the GNU General Public License as published by
   6    the Free Software Foundation; either version 2, or (at your option)
   7    any later version.
   8
   9    This program 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
  12    GNU General Public License for more details.
  13
  14    You should have received a copy of the GNU General Public License along
  15    with this program; if not, write to the Free Software Foundation,
  16    Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.  */
  17
  18 /*
  19
  20 @deftypefn Supplemental void* memmem (const void *@var{haystack}, @
  21   size_t @var{haystack_len} const void *@var{needle}, size_t @var{needle_len})
  22
  23 Returns a pointer to the first occurrence of @var{needle} (length
  24 @var{needle_len}) in @var{haystack} (length @var{haystack_len}).
  25 Returns @code{NULL} if not found.
  26
  27 @end deftypefn
  28
  29 */
  30
  31 #ifndef _LIBC
  32 # include <config.h>
  33 #endif
  34
  35 #include <stddef.h>
  36 #include <string.h>
  37
  38 #ifndef _LIBC
  39 # define __builtin_expect(expr, val)   (expr)
  40 #endif
  41
  42 #undef memmem
  43
  44 /* Return the first occurrence of NEEDLE in HAYSTACK.  */
  45 void *
  46 memmem (const void *haystack, size_t haystack_len, const void *needle,
  47         size_t needle_len)
  48 {
  49   const char *begin;
  50   const char *const last_possible
  51     = (const char *) haystack + haystack_len - needle_len;
  52
  53   if (needle_len == 0)
  54     /* The first occurrence of the empty string is deemed to occur at
  55        the beginning of the string.  */
  56     return (void *) haystack;
  57
  58   /* Sanity check, otherwise the loop might search through the whole
  59      memory.  */
  60   if (__builtin_expect (haystack_len < needle_len, 0))
  61     return NULL;
  62
  63   for (begin = (const char *) haystack; begin <= last_possible; ++begin)
  64     if (begin[0] == ((const char *) needle)[0] &&
  65         !memcmp ((const void *) &begin[1],
  66                  (const void *) ((const char *) needle + 1),
  67                  needle_len - 1))
  68       return (void *) begin;
  69
  70   return NULL;
  71 }