137 lines
5.3 KiB
Diff
137 lines
5.3 KiB
Diff
commit 284f42bc778e487dfd5dff5c01959f93b9e0c4f5
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Author: Wilco Dijkstra <wdijkstr@arm.com>
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Date: Fri Aug 3 17:24:12 2018 +0100
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Simplify and speedup strstr/strcasestr first match
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Looking at the benchtests, both strstr and strcasestr spend a lot of time
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in a slow initialization loop handling one character per iteration.
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This can be simplified and use the much faster strlen/strnlen/strchr/memcmp.
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Read ahead a few cachelines to reduce the number of strnlen calls, which
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improves performance by ~3-4%. This patch improves the time taken for the
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full strstr benchtest by >40%.
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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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diff --git a/string/strcasestr.c b/string/strcasestr.c
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index 421764bd1b0ff22e..8aa76037dcc052f3 100644
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--- a/string/strcasestr.c
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+++ b/string/strcasestr.c
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@@ -59,31 +59,22 @@
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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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-
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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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+
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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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+
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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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@@ -91,10 +82,10 @@ 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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diff --git a/string/strstr.c b/string/strstr.c
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index 79ebcc75329d0b17..f74d7189ed1319f6 100644
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--- a/string/strstr.c
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+++ b/string/strstr.c
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@@ -51,33 +51,32 @@
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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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-
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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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+
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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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+
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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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+
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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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-
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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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+
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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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