From 284f42bc778e487dfd5dff5c01959f93b9e0c4f5 Mon Sep 17 00:00:00 2001 From: Wilco Dijkstra Date: Fri, 3 Aug 2018 17:24:12 +0100 Subject: 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. --- string/strstr.c | 43 +++++++++++++++++++++---------------------- 1 file changed, 21 insertions(+), 22 deletions(-) (limited to 'string/strstr.c') diff --git a/string/strstr.c b/string/strstr.c index 265e9f310c..33acdc5442 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 -- cgit 1.4.1