sysdeps/generic/memmem.c

   1 /* Copyright (C) 1991, 1992, 1993, 1994, 1996 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 Library General Public License as
   6 published by the Free Software Foundation; either version 2 of the
   7 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 Library General Public License for more details.
  13
  14 You should have received a copy of the GNU Library General Public
  15 License along with the GNU C Library; see the file COPYING.LIB.  If
  16 not, write to the Free Software Foundation, Inc., 675 Mass Ave,
  17 Cambridge, MA 02139, USA.  */
  18
  19 #include <ansidecl.h>
  20 #include <stddef.h>
  21 #include <string.h>
  22
  23
  24 /* Return the first occurrence of NEEDLE in HAYSTACK.  */
  25 PTR
  26 DEFUN(memmem, (haystack, haystack_len,
  27                needle, needle_len),
  28       CONST PTRCONST haystack AND CONST size_t haystack_len AND
  29       CONST PTRCONST needle AND CONST size_t needle_len)
  30 {
  31   register CONST char *begin;
  32   register CONST char *CONST last_possible
  33     = (CONST char *) haystack + haystack_len - needle_len;
  34
  35   if (needle_len == 0)
  36     /* The first occurrence of the empty string is deemed to occur at
  37        the end of the string.  */
  38     return (PTR) &((CONST char *) haystack)[haystack_len - 1];
  39
  40   for (begin = (CONST char *) haystack; begin <= last_possible; ++begin)
  41     if (begin[0] == ((CONST char *) needle)[0] &&
  42         !memcmp ((CONST PTR) &begin[1],
  43                  (CONST PTR) ((CONST char *) needle + 1),
  44                  needle_len - 1))
  45       return (PTR) begin;
  46
  47   return NULL;
  48 }