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authorWilco Dijkstra <wdijkstr@arm.com>2018-08-03 17:24:12 +0100
committerWilco Dijkstra <wdijkstr@arm.com>2018-08-03 17:24:12 +0100
commit284f42bc778e487dfd5dff5c01959f93b9e0c4f5 (patch)
tree4480c734a632b75194a0b4fd062b65057d6e2ad7 /string
parent430388d5dc0e1861b869096f4f5d946d7d74232a (diff)
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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.
Diffstat (limited to 'string')
-rw-r--r--string/strcasestr.c37
-rw-r--r--string/strstr.c43
2 files changed, 35 insertions, 45 deletions
diff --git a/string/strcasestr.c b/string/strcasestr.c
index 5909fe3cdba..1f6b7b846f8 100644
--- a/string/strcasestr.c
+++ b/string/strcasestr.c
@@ -58,31 +58,22 @@
case-insensitive comparison. This function gives unspecified
results in multibyte locales. */
char *
-STRCASESTR (const char *haystack_start, const char *needle_start)
+STRCASESTR (const char *haystack, const char *needle)
{
- const char *haystack = haystack_start;
- const char *needle = needle_start;
size_t needle_len; /* Length of NEEDLE. */
size_t haystack_len; /* Known minimum length of HAYSTACK. */
- bool ok = true; /* True if NEEDLE is prefix of HAYSTACK. */
-
- /* Determine length of NEEDLE, and in the process, make sure
- HAYSTACK is at least as long (no point processing all of a long
- NEEDLE if HAYSTACK is too short). */
- while (*haystack && *needle)
- {
- ok &= (TOLOWER ((unsigned char) *haystack)
- == TOLOWER ((unsigned char) *needle));
- haystack++;
- needle++;
- }
- if (*needle)
+
+ /* Handle empty NEEDLE special case. */
+ if (needle[0] == '\0')
+ return (char *) haystack;
+
+ /* Ensure HAYSTACK length is at least as long as NEEDLE length.
+ Since a match may occur early on in a huge HAYSTACK, use strnlen
+ and read ahead a few cachelines for improved performance. */
+ needle_len = strlen (needle);
+ haystack_len = __strnlen (haystack, needle_len + 256);
+ if (haystack_len < needle_len)
return NULL;
- if (ok)
- return (char *) haystack_start;
- needle_len = needle - needle_start;
- haystack = haystack_start + 1;
- haystack_len = needle_len - 1;
/* Perform the search. Abstract memory is considered to be an array
of 'unsigned char' values, not an array of 'char' values. See
@@ -90,10 +81,10 @@ STRCASESTR (const char *haystack_start, const char *needle_start)
if (needle_len < LONG_NEEDLE_THRESHOLD)
return two_way_short_needle ((const unsigned char *) haystack,
haystack_len,
- (const unsigned char *) needle_start,
+ (const unsigned char *) needle,
needle_len);
return two_way_long_needle ((const unsigned char *) haystack, haystack_len,
- (const unsigned char *) needle_start,
+ (const unsigned char *) needle,
needle_len);
}
diff --git a/string/strstr.c b/string/strstr.c
index 265e9f310ce..33acdc5442d 100644
--- a/string/strstr.c
+++ b/string/strstr.c
@@ -50,33 +50,32 @@
if NEEDLE is empty, otherwise NULL if NEEDLE is not found in
HAYSTACK. */
char *
-STRSTR (const char *haystack_start, const char *needle_start)
+STRSTR (const char *haystack, const char *needle)
{
- const char *haystack = haystack_start;
- const char *needle = needle_start;
size_t needle_len; /* Length of NEEDLE. */
size_t haystack_len; /* Known minimum length of HAYSTACK. */
- bool ok = true; /* True if NEEDLE is prefix of HAYSTACK. */
-
- /* Determine length of NEEDLE, and in the process, make sure
- HAYSTACK is at least as long (no point processing all of a long
- NEEDLE if HAYSTACK is too short). */
- while (*haystack && *needle)
- ok &= *haystack++ == *needle++;
- if (*needle)
+
+ /* Handle empty NEEDLE special case. */
+ if (needle[0] == '\0')
+ return (char *) haystack;
+
+ /* Skip until we find the first matching char from NEEDLE. */
+ haystack = strchr (haystack, needle[0]);
+ if (haystack == NULL || needle[1] == '\0')
+ return (char *) haystack;
+
+ /* Ensure HAYSTACK length is at least as long as NEEDLE length.
+ Since a match may occur early on in a huge HAYSTACK, use strnlen
+ and read ahead a few cachelines for improved performance. */
+ needle_len = strlen (needle);
+ haystack_len = __strnlen (haystack, needle_len + 256);
+ if (haystack_len < needle_len)
return NULL;
- if (ok)
- return (char *) haystack_start;
-
- /* Reduce the size of haystack using strchr, since it has a smaller
- linear coefficient than the Two-Way algorithm. */
- needle_len = needle - needle_start;
- haystack = strchr (haystack_start + 1, *needle_start);
- if (!haystack || __builtin_expect (needle_len == 1, 0))
+
+ /* Check whether we have a match. This improves performance since we avoid
+ the initialization overhead of the two-way algorithm. */
+ if (memcmp (haystack, needle, needle_len) == 0)
return (char *) haystack;
- needle -= needle_len;
- haystack_len = (haystack > haystack_start + needle_len ? 1
- : needle_len + haystack_start - haystack);
/* Perform the search. Abstract memory is considered to be an array
of 'unsigned char' values, not an array of 'char' values. See