forked from KolibriOS/kolibrios
103 lines
3.0 KiB
C
103 lines
3.0 KiB
C
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/* Byte-wise substring search, using the Two-Way algorithm.
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* Copyright (C) 2008 Eric Blake
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* Permission to use, copy, modify, and distribute this software
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* is freely granted, provided that this notice is preserved.
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*/
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/*
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FUNCTION
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<<memmem>>---find memory segment
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INDEX
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memmem
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ANSI_SYNOPSIS
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#include <string.h>
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char *memmem(const void *<[s1]>, size_t <[l1]>, const void *<[s2]>,
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size_t <[l2]>);
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DESCRIPTION
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Locates the first occurrence in the memory region pointed to
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by <[s1]> with length <[l1]> of the sequence of bytes pointed
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to by <[s2]> of length <[l2]>. If you already know the
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lengths of your haystack and needle, <<memmem>> can be much
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faster than <<strstr>>.
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RETURNS
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Returns a pointer to the located segment, or a null pointer if
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<[s2]> is not found. If <[l2]> is 0, <[s1]> is returned.
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PORTABILITY
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<<memmem>> is a newlib extension.
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<<memmem>> requires no supporting OS subroutines.
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QUICKREF
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memmem pure
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*/
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#include <string.h>
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#if !defined(PREFER_SIZE_OVER_SPEED) && !defined(__OPTIMIZE_SIZE__)
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# define RETURN_TYPE void *
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# define AVAILABLE(h, h_l, j, n_l) ((j) <= (h_l) - (n_l))
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# include "str-two-way.h"
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#endif
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void *
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_DEFUN (memmem, (haystack_start, haystack_len, needle_start, needle_len),
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const void *haystack_start _AND
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size_t haystack_len _AND
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const void *needle_start _AND
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size_t needle_len)
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{
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/* Abstract memory is considered to be an array of 'unsigned char' values,
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not an array of 'char' values. See ISO C 99 section 6.2.6.1. */
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const unsigned char *haystack = (const unsigned char *) haystack_start;
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const unsigned char *needle = (const unsigned char *) needle_start;
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if (needle_len == 0)
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/* The first occurrence of the empty string is deemed to occur at
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the beginning of the string. */
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return (void *) haystack;
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#if defined(PREFER_SIZE_OVER_SPEED) || defined(__OPTIMIZE_SIZE__)
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/* Less code size, but quadratic performance in the worst case. */
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while (needle_len <= haystack_len)
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{
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if (!memcmp (haystack, needle, needle_len))
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return (void *) haystack;
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haystack++;
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haystack_len--;
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}
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return NULL;
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#else /* compilation for speed */
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/* Larger code size, but guaranteed linear performance. */
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/* Sanity check, otherwise the loop might search through the whole
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memory. */
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if (haystack_len < needle_len)
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return NULL;
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/* Use optimizations in memchr when possible, to reduce the search
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size of haystack using a linear algorithm with a smaller
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coefficient. However, avoid memchr for long needles, since we
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can often achieve sublinear performance. */
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if (needle_len < LONG_NEEDLE_THRESHOLD)
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{
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haystack = memchr (haystack, *needle, haystack_len);
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if (!haystack || needle_len == 1)
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return (void *) haystack;
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haystack_len -= haystack - (const unsigned char *) haystack_start;
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if (haystack_len < needle_len)
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return NULL;
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return two_way_short_needle (haystack, haystack_len, needle, needle_len);
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}
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return two_way_long_needle (haystack, haystack_len, needle, needle_len);
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#endif /* compilation for speed */
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}
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