/* Return the offset of one string within another.

   Copyright (C) 1994-2018 Free Software Foundation, Inc.

   This file is part of the GNU C Library.

   The GNU C Library 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 of the License, or (at your option) any later version.

   The GNU C Library 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 the GNU C Library; if not, see

   <http://www.gnu.org/licenses/>.  */

#ifndef _LIBC

# include <config.h>

#endif

#include <string.h>

#define RETURN_TYPE char *

#define AVAILABLE(h, h_l, j, n_l)			\

  (((j) + (n_l) <= (h_l)) \

   || ((h_l) += __strnlen ((void*)((h) + (h_l)), (n_l) + 512), \

       (j) + (n_l) <= (h_l)))

#include "str-two-way.h"

#undef strstr

#ifndef STRSTR

#define STRSTR strstr

#endif

static inline char *

strstr2 (const unsigned char *hs, const unsigned char *ne)

{

  uint32_t h1 = (ne[0] << 16) | ne[1];

  uint32_t h2 = 0;

  for (int c = hs[0]; h1 != h2 && c != 0; c = *++hs)

      h2 = (h2 << 16) | c;

  return h1 == h2 ? (char *)hs - 2 : NULL;

}

static inline char *

strstr3 (const unsigned char *hs, const unsigned char *ne)

{

  uint32_t h1 = ((uint32_t)ne[0] << 24) | (ne[1] << 16) | (ne[2] << 8);

  uint32_t h2 = 0;

  for (int c = hs[0]; h1 != h2 && c != 0; c = *++hs)

      h2 = (h2 | c) << 8;

  return h1 == h2 ? (char *)hs - 3 : NULL;

}

/* Hash character pairs so a small shift table can be used.  All bits of

   p[0] are included, but not all bits from p[-1].  So if two equal hashes

   match on p[-1], p[0] matches too.  Hash collisions are harmless and result

   in smaller shifts.  */

#define hash2(p) (((size_t)(p)[0] - ((size_t)(p)[-1] << 3)) % sizeof (shift))

/* Fast strstr algorithm with guaranteed linear-time performance.

   Small needles up to size 3 use a dedicated linear search.  Longer needles

   up to size 256 use a novel modified Horspool algorithm.  It hashes pairs

   of characters to quickly skip past mismatches.  The main search loop only

   exits if the last 2 characters match, avoiding unnecessary calls to memcmp

   and allowing for a larger skip if there is no match.  A self-adapting

   filtering check is used to quickly detect mismatches in long needles.

   By limiting the needle length to 256, the shift table can be reduced to 8

   bits per entry, lowering preprocessing overhead and minimizing cache effects.

   The limit also implies worst-case performance is linear.

   Needles larger than 256 characters use the linear-time Two-Way algorithm.  */

char *

STRSTR (const char *haystack, const char *needle)

{

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

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

  /* Handle short needle special cases first.  */

  if (ne[0] == '\0')

    return (char *)hs;

  hs = (const unsigned char *)strchr ((const char*)hs, ne[0]);

  if (hs == NULL || ne[1] == '\0')

    return (char*)hs;

  if (ne[2] == '\0')

    return strstr2 (hs, ne);

  if (ne[3] == '\0')

    return strstr3 (hs, ne);

  /* Ensure haystack length is at least as long as needle length.

     Since a match may occur early on in a huge haystack, use strnlen

     and read ahead a few cachelines for improved performance.  */

  size_t ne_len = strlen ((const char*)ne);

  size_t hs_len = __strnlen ((const char*)hs, ne_len | 512);

  if (hs_len < ne_len)

    return NULL;

  /* Check whether we have a match.  This improves performance since we

     avoid initialization overheads.  */

  if (memcmp (hs, ne, ne_len) == 0)

    return (char *) hs;

  /* Use Two-Way algorithm for very long needles.  */

  if (__glibc_unlikely (ne_len > 256))

    return two_way_long_needle (hs, hs_len, ne, ne_len);

  const unsigned char *end = hs + hs_len - ne_len;

  uint8_t shift[256];

  size_t tmp, shift1;

  size_t m1 = ne_len - 1;

  size_t offset = 0;

  /* Initialize bad character shift hash table.  */

  memset (shift, 0, sizeof (shift));

  for (int i = 1; i < m1; i++)

    shift[hash2 (ne + i)] = i;

  /* Shift1 is the amount we can skip after matching the hash of the

     needle end but not the full needle.  */

  shift1 = m1 - shift[hash2 (ne + m1)];

  shift[hash2 (ne + m1)] = m1;

  while (1)

    {

      if (__glibc_unlikely (hs > end))

	{

	  end += __strnlen ((const char*)end + m1 + 1, 2048);

	  if (hs > end)

	    return NULL;

	}

      /* Skip past character pairs not in the needle.  */

      do

	{

	  hs += m1;

	  tmp = shift[hash2 (hs)];

	}

      while (tmp == 0 && hs <= end);

      /* If the match is not at the end of the needle, shift to the end

	 and continue until we match the hash of the needle end.  */

      hs -= tmp;

      if (tmp < m1)

	continue;

      /* Hash of the last 2 characters matches.  If the needle is long,

	 try to quickly filter out mismatches.  */

      if (m1 < 15 || memcmp (hs + offset, ne + offset, 8) == 0)

	{

	  if (memcmp (hs, ne, m1) == 0)

	    return (void *) hs;

	  /* Adjust filter offset when it doesn't find the mismatch.  */

	  offset = (offset >= 8 ? offset : m1) - 8;

	}

      /* Skip based on matching the hash of the needle end.  */

      hs += shift1;

    }

}

libc_hidden_builtin_def (strstr)