122 lines
2.9 KiB
C
122 lines
2.9 KiB
C
/*
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FUNCTION
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<<strstr>>---find string segment
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INDEX
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strstr
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ANSI_SYNOPSIS
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#include <string.h>
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char *strstr(const char *<[s1]>, const char *<[s2]>);
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TRAD_SYNOPSIS
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#include <string.h>
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char *strstr(<[s1]>, <[s2]>)
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char *<[s1]>;
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char *<[s2]>;
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DESCRIPTION
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Locates the first occurrence in the string pointed to by <[s1]> of
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the sequence of characters in the string pointed to by <[s2]>
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(excluding the terminating null character).
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RETURNS
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Returns a pointer to the located string segment, or a null
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pointer if the string <[s2]> is not found. If <[s2]> points to
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a string with zero length, <[s1]> is returned.
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PORTABILITY
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<<strstr>> is ANSI C.
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<<strstr>> requires no supporting OS subroutines.
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QUICKREF
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strstr ansi 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 char *
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# define AVAILABLE(h, h_l, j, n_l) \
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(!memchr ((h) + (h_l), '\0', (j) + (n_l) - (h_l)) \
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&& ((h_l) = (j) + (n_l)))
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# include "str-two-way.h"
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#endif
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char *
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_DEFUN (strstr, (searchee, lookfor),
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_CONST char *searchee _AND
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_CONST char *lookfor)
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{
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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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if (*searchee == 0)
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{
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if (*lookfor)
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return (char *) NULL;
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return (char *) searchee;
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}
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while (*searchee)
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{
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size_t i;
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i = 0;
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while (1)
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{
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if (lookfor[i] == 0)
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{
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return (char *) searchee;
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}
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if (lookfor[i] != searchee[i])
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{
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break;
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}
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i++;
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}
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searchee++;
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}
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return (char *) NULL;
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#else /* compilation for speed */
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/* Larger code size, but guaranteed linear performance. */
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const char *haystack = searchee;
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const char *needle = lookfor;
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size_t needle_len; /* Length of NEEDLE. */
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size_t haystack_len; /* Known minimum length of HAYSTACK. */
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int ok = 1; /* True if NEEDLE is prefix of HAYSTACK. */
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/* Determine length of NEEDLE, and in the process, make sure
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HAYSTACK is at least as long (no point processing all of a long
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NEEDLE if HAYSTACK is too short). */
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while (*haystack && *needle)
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ok &= *haystack++ == *needle++;
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if (*needle)
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return NULL;
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if (ok)
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return (char *) searchee;
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/* Reduce the size of haystack using strchr, since it has a smaller
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linear coefficient than the Two-Way algorithm. */
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needle_len = needle - lookfor;
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haystack = strchr (searchee + 1, *lookfor);
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if (!haystack || needle_len == 1)
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return (char *) haystack;
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haystack_len = (haystack > searchee + needle_len ? 1
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: needle_len + searchee - haystack);
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/* Perform the search. */
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if (needle_len < LONG_NEEDLE_THRESHOLD)
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return two_way_short_needle ((const unsigned char *) haystack,
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haystack_len,
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(const unsigned char *) lookfor, needle_len);
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return two_way_long_needle ((const unsigned char *) haystack, haystack_len,
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(const unsigned char *) lookfor, needle_len);
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#endif /* compilation for speed */
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}
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