1  /* Return the offset of one string within another.
       2     Copyright (C) 1994-2023 Free Software Foundation, Inc.
       3     This file is part of the GNU C Library.
       4  
       5     The GNU C Library is free software; you can redistribute it and/or
       6     modify it under the terms of the GNU Lesser General Public
       7     License as published by the Free Software Foundation; either
       8     version 2.1 of the License, or (at your option) any later version.
       9  
      10     The GNU C Library 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 GNU
      13     Lesser General Public License for more details.
      14  
      15     You should have received a copy of the GNU Lesser General Public
      16     License along with the GNU C Library; if not, see
      17     <https://www.gnu.org/licenses/>.  */
      18  
      19  /*
      20   * My personal strstr() implementation that beats most other algorithms.
      21   * Until someone tells me otherwise, I assume that this is the
      22   * fastest implementation of strstr() in C.
      23   * I deliberately chose not to comment it.  You should have at least
      24   * as much fun trying to understand it, as I had to write it :-).
      25   *
      26   * Stephen R. van den Berg, berg@pool.informatik.rwth-aachen.de	*/
      27  
      28  /* Specification.  */
      29  #include <string.h>
      30  
      31  #include <ctype.h>
      32  #include <stdbool.h>
      33  #include <strings.h>
      34  
      35  #define TOLOWER(Ch) tolower (Ch)
      36  
      37  /* Two-Way algorithm.  */
      38  #define RETURN_TYPE char *
      39  #define AVAILABLE(h, h_l, j, n_l)			\
      40    (((j) + (n_l) <= (h_l)) \
      41     || ((h_l) += __strnlen ((void*)((h) + (h_l)), (n_l) + 512), \
      42         (j) + (n_l) <= (h_l)))
      43  #define CHECK_EOL (1)
      44  #define RET0_IF_0(a) if (!a) goto ret0
      45  #define CANON_ELEMENT(c) TOLOWER (c)
      46  #define CMP_FUNC(p1, p2, l)				\
      47    __strncasecmp ((const char *) (p1), (const char *) (p2), l)
      48  #include "str-two-way.h"
      49  
      50  #undef strcasestr
      51  #undef __strcasestr
      52  
      53  #ifndef STRCASESTR
      54  #define STRCASESTR __strcasestr
      55  #endif
      56  
      57  
      58  /* Find the first occurrence of NEEDLE in HAYSTACK, using
      59     case-insensitive comparison.  This function gives unspecified
      60     results in multibyte locales.  */
      61  char *
      62  STRCASESTR (const char *haystack, const char *needle)
      63  {
      64    size_t needle_len; /* Length of NEEDLE.  */
      65    size_t haystack_len; /* Known minimum length of HAYSTACK.  */
      66  
      67    /* Handle empty NEEDLE special case.  */
      68    if (needle[0] == '\0')
      69      return (char *) haystack;
      70  
      71    /* Ensure HAYSTACK length is at least as long as NEEDLE length.
      72       Since a match may occur early on in a huge HAYSTACK, use strnlen
      73       and read ahead a few cachelines for improved performance.  */
      74    needle_len = strlen (needle);
      75    haystack_len = __strnlen (haystack, needle_len + 256);
      76    if (haystack_len < needle_len)
      77      return NULL;
      78  
      79    /* Perform the search.  Abstract memory is considered to be an array
      80       of 'unsigned char' values, not an array of 'char' values.  See
      81       ISO C 99 section 6.2.6.1.  */
      82    if (needle_len < LONG_NEEDLE_THRESHOLD)
      83      return two_way_short_needle ((const unsigned char *) haystack,
      84  				 haystack_len,
      85  				 (const unsigned char *) needle,
      86  				 needle_len);
      87    return two_way_long_needle ((const unsigned char *) haystack, haystack_len,
      88  			      (const unsigned char *) needle,
      89  			      needle_len);
      90  }
      91  
      92  #undef LONG_NEEDLE_THRESHOLD
      93  
      94  #ifndef NO_ALIAS
      95  weak_alias (__strcasestr, strcasestr)
      96  #endif