/* Copyright (C) 1991-1994, 1996-1998, 2000, 2004, 2007-2020 Free Software

   Foundation, Inc.

   This file is part of the GNU C Library.

   This program is free software; you can redistribute it and/or modify

   it under the terms of the GNU Lesser General Public License as published by

   the Free Software Foundation; either version 2.1, or (at your option)

   any later version.

   This program is distributed in the hope that it will be useful,

   but WITHOUT ANY WARRANTY; without even the implied warranty of

   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the

   GNU Lesser General Public License for more details.

   You should have received a copy of the GNU Lesser General Public License along

   with this program; if not, see <https://www.gnu.org/licenses/>.  */

/* This particular implementation was written by Eric Blake, 2008.  */

#ifndef _LIBC

# include <config.h>

#endif

/* Specification of memmem.  */

#include <string.h>

#define RETURN_TYPE void *

#define AVAILABLE(h, h_l, j, n_l) ((j) <= (h_l) - (n_l))

#include "str-two-way.h"

/* Return the first occurrence of NEEDLE in HAYSTACK.  Return HAYSTACK

   if NEEDLE_LEN is 0, otherwise NULL if NEEDLE is not found in

   HAYSTACK.  */

void *

memmem (const void *haystack_start, size_t haystack_len,

        const void *needle_start, size_t needle_len)

{

  /* Abstract memory is considered to be an array of 'unsigned char' values,

     not an array of 'char' values.  See ISO C 99 section 6.2.6.1.  */

  const unsigned char *haystack = (const unsigned char *) haystack_start;

  const unsigned char *needle = (const unsigned char *) needle_start;

  if (needle_len == 0)

    /* The first occurrence of the empty string is deemed to occur at

       the beginning of the string.  */

    return (void *) haystack;

  /* Sanity check, otherwise the loop might search through the whole

     memory.  */

  if (__builtin_expect (haystack_len < needle_len, 0))

    return NULL;

  /* Use optimizations in memchr when possible, to reduce the search

     size of haystack using a linear algorithm with a smaller

     coefficient.  However, avoid memchr for long needles, since we

     can often achieve sublinear performance.  */

  if (needle_len < LONG_NEEDLE_THRESHOLD)

    {

      haystack = memchr (haystack, *needle, haystack_len);

      if (!haystack || __builtin_expect (needle_len == 1, 0))

        return (void *) haystack;

      haystack_len -= haystack - (const unsigned char *) haystack_start;

      if (haystack_len < needle_len)

        return NULL;

      return two_way_short_needle (haystack, haystack_len, needle, needle_len);

    }

  else

    return two_way_long_needle (haystack, haystack_len, needle, needle_len);

}

#undef LONG_NEEDLE_THRESHOLD