root/lib/memmem.c

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DEFINITIONS

This source file includes following definitions.
  1. memmem

     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 memmem.  */
    25 #include <string.h>
    26 
    27 #define RETURN_TYPE void *
    28 #define AVAILABLE(h, h_l, j, n_l) ((j) <= (h_l) - (n_l))
    29 #include "str-two-way.h"
    30 
    31 /* Return the first occurrence of NEEDLE in HAYSTACK.  Return HAYSTACK
    32    if NEEDLE_LEN is 0, otherwise NULL if NEEDLE is not found in
    33    HAYSTACK.  */
    34 void *
    35 memmem (const void *haystack_start, size_t haystack_len,
    36         const void *needle_start, size_t needle_len)
    37 {
    38   /* Abstract memory is considered to be an array of 'unsigned char' values,
    39      not an array of 'char' values.  See ISO C 99 section 6.2.6.1.  */
    40   const unsigned char *haystack = (const unsigned char *) haystack_start;
    41   const unsigned char *needle = (const unsigned char *) needle_start;
    42 
    43   if (needle_len == 0)
    44     /* The first occurrence of the empty string is deemed to occur at
    45        the beginning of the string.  */
    46     return (void *) haystack;
    47 
    48   /* Sanity check, otherwise the loop might search through the whole
    49      memory.  */
    50   if (__builtin_expect (haystack_len < needle_len, 0))
    51     return NULL;
    52 
    53   /* Use optimizations in memchr when possible, to reduce the search
    54      size of haystack using a linear algorithm with a smaller
    55      coefficient.  However, avoid memchr for long needles, since we
    56      can often achieve sublinear performance.  */
    57   if (needle_len < LONG_NEEDLE_THRESHOLD)
    58     {
    59       haystack = memchr (haystack, *needle, haystack_len);
    60       if (!haystack || __builtin_expect (needle_len == 1, 0))
    61         return (void *) haystack;
    62       haystack_len -= haystack - (const unsigned char *) haystack_start;
    63       if (haystack_len < needle_len)
    64         return NULL;
    65       return two_way_short_needle (haystack, haystack_len, needle, needle_len);
    66     }
    67   else
    68     return two_way_long_needle (haystack, haystack_len, needle, needle_len);
    69 }
    70 
    71 #undef LONG_NEEDLE_THRESHOLD

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