1  /* Copyright (C) 1991-1994, 1996-1998, 2000, 2004, 2007-2023 Free Software
       2     Foundation, Inc.
       3     This file is part of the GNU C Library.
       4  
       5     This file is free software: you can redistribute it and/or modify
       6     it under the terms of the GNU Lesser General Public License as
       7     published by the Free Software Foundation; either version 2.1 of the
       8     License, or (at your option) any later version.
       9  
      10     This file is distributed in the hope that it will be useful,
      11     but WITHOUT ANY WARRANTY; without even the implied warranty of
      12     MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
      13     GNU Lesser General Public License for more details.
      14  
      15     You should have received a copy of the GNU Lesser General Public License
      16     along with this program.  If not, see <https://www.gnu.org/licenses/>.  */
      17  
      18  /* This particular implementation was written by Eric Blake, 2008.  */
      19  
      20  #ifndef _LIBC
      21  # include <config.h>
      22  #endif
      23  
      24  /* Specification of strstr.  */
      25  #include <string.h>
      26  
      27  #define RETURN_TYPE char *
      28  #define AVAILABLE(h, h_l, j, n_l)                       \
      29    (!memchr ((h) + (h_l), '\0', (j) + (n_l) - (h_l))     \
      30     && ((h_l) = (j) + (n_l)))
      31  #include "str-two-way.h"
      32  
      33  /* Return the first occurrence of NEEDLE in HAYSTACK.  Return HAYSTACK
      34     if NEEDLE is empty, otherwise NULL if NEEDLE is not found in
      35     HAYSTACK.  */
      36  char *
      37  strstr (const char *haystack_start, const char *needle_start)
      38  {
      39    const char *haystack = haystack_start;
      40    const char *needle = needle_start;
      41    size_t needle_len; /* Length of NEEDLE.  */
      42    size_t haystack_len; /* Known minimum length of HAYSTACK.  */
      43    bool ok = true; /* True if NEEDLE is prefix of HAYSTACK.  */
      44  
      45    /* Determine length of NEEDLE, and in the process, make sure
      46       HAYSTACK is at least as long (no point processing all of a long
      47       NEEDLE if HAYSTACK is too short).  */
      48    while (*haystack && *needle)
      49      ok &= *haystack++ == *needle++;
      50    if (*needle)
      51      return NULL;
      52    if (ok)
      53      return (char *) haystack_start;
      54  
      55    /* Reduce the size of haystack using strchr, since it has a smaller
      56       linear coefficient than the Two-Way algorithm.  */
      57    needle_len = needle - needle_start;
      58    haystack = strchr (haystack_start + 1, *needle_start);
      59    if (!haystack || __builtin_expect (needle_len == 1, 0))
      60      return (char *) haystack;
      61    needle -= needle_len;
      62    haystack_len = (haystack > haystack_start + needle_len ? 1
      63                    : needle_len + haystack_start - haystack);
      64  
      65    /* Perform the search.  Abstract memory is considered to be an array
      66       of 'unsigned char' values, not an array of 'char' values.  See
      67       ISO C 99 section 6.2.6.1.  */
      68    if (needle_len < LONG_NEEDLE_THRESHOLD)
      69      return two_way_short_needle ((const unsigned char *) haystack,
      70                                   haystack_len,
      71                                   (const unsigned char *) needle, needle_len);
      72    return two_way_long_needle ((const unsigned char *) haystack, haystack_len,
      73                                (const unsigned char *) needle, needle_len);
      74  }
      75  
      76  #undef LONG_NEEDLE_THRESHOLD