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Simplify and speedup strstr/strcasestr first match
Looking at the benchtests, both strstr and strcasestr spend a lot of time in a slow initialization loop handling one character per iteration. This can be simplified and use the much faster strlen/strnlen/strchr/memcmp. Read ahead a few cachelines to reduce the number of strnlen calls, which improves performance by ~3-4%. This patch improves the time taken for the full strstr benchtest by >40%. * string/strcasestr.c (STRCASESTR): Simplify and speedup first match. * string/strstr.c (AVAILABLE): Likewise.
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@ -1,3 +1,8 @@
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2018-08-03 Wilco Dijkstra <wdijkstr@arm.com>
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* string/strcasestr.c (STRCASESTR): Simplify and speedup first match.
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* string/strstr.c (AVAILABLE): Likewise.
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2018-08-03 H.J. Lu <hongjiu.lu@intel.com>
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* sysdeps/i386/i686/multiarch/bzero-ia32.S: Don't include
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@ -58,31 +58,22 @@
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case-insensitive comparison. This function gives unspecified
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results in multibyte locales. */
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char *
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STRCASESTR (const char *haystack_start, const char *needle_start)
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STRCASESTR (const char *haystack, const char *needle)
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{
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const char *haystack = haystack_start;
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const char *needle = needle_start;
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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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bool ok = true; /* 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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{
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ok &= (TOLOWER ((unsigned char) *haystack)
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== TOLOWER ((unsigned char) *needle));
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haystack++;
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needle++;
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}
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if (*needle)
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/* Handle empty NEEDLE special case. */
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if (needle[0] == '\0')
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return (char *) haystack;
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/* Ensure HAYSTACK length is at least as long as NEEDLE length.
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Since a match may occur early on in a huge HAYSTACK, use strnlen
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and read ahead a few cachelines for improved performance. */
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needle_len = strlen (needle);
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haystack_len = __strnlen (haystack, needle_len + 256);
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if (haystack_len < needle_len)
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return NULL;
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if (ok)
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return (char *) haystack_start;
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needle_len = needle - needle_start;
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haystack = haystack_start + 1;
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haystack_len = needle_len - 1;
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/* Perform the search. Abstract memory is considered to be an array
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of 'unsigned char' values, not an array of 'char' values. See
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@ -90,10 +81,10 @@ STRCASESTR (const char *haystack_start, const char *needle_start)
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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 *) needle_start,
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(const unsigned char *) needle,
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needle_len);
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return two_way_long_needle ((const unsigned char *) haystack, haystack_len,
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(const unsigned char *) needle_start,
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(const unsigned char *) needle,
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needle_len);
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}
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@ -50,33 +50,32 @@
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if NEEDLE is empty, otherwise NULL if NEEDLE is not found in
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HAYSTACK. */
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char *
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STRSTR (const char *haystack_start, const char *needle_start)
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STRSTR (const char *haystack, const char *needle)
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{
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const char *haystack = haystack_start;
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const char *needle = needle_start;
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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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bool ok = true; /* 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 *) haystack_start;
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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 - needle_start;
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haystack = strchr (haystack_start + 1, *needle_start);
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if (!haystack || __builtin_expect (needle_len == 1, 0))
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/* Handle empty NEEDLE special case. */
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if (needle[0] == '\0')
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return (char *) haystack;
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/* Skip until we find the first matching char from NEEDLE. */
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haystack = strchr (haystack, needle[0]);
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if (haystack == NULL || needle[1] == '\0')
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return (char *) haystack;
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/* Ensure HAYSTACK length is at least as long as NEEDLE length.
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Since a match may occur early on in a huge HAYSTACK, use strnlen
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and read ahead a few cachelines for improved performance. */
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needle_len = strlen (needle);
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haystack_len = __strnlen (haystack, needle_len + 256);
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if (haystack_len < needle_len)
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return NULL;
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/* Check whether we have a match. This improves performance since we avoid
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the initialization overhead of the two-way algorithm. */
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if (memcmp (haystack, needle, needle_len) == 0)
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return (char *) haystack;
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needle -= needle_len;
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haystack_len = (haystack > haystack_start + needle_len ? 1
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: needle_len + haystack_start - haystack);
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/* Perform the search. Abstract memory is considered to be an array
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of 'unsigned char' values, not an array of 'char' values. See
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