From: Wilco Dijkstra <Wilco.Dijkstra@arm.com>
To: "tirtajames45@gmail.com" <tirtajames45@gmail.com>
Cc: 'GNU C Library' <libc-alpha@sourceware.org>
Subject: [PATCH] strcasestr: check if ne[0] is in hs with strchr or strpbrk as does strstr
Date: Thu, 7 Sep 2023 22:14:16 +0000 [thread overview]
Message-ID: <PAWPR08MB89829F6BE1B835956E61AEE983EEA@PAWPR08MB8982.eurprd08.prod.outlook.com> (raw)
Hi James,
This looks correct to me, but what about performance?
+ if (isalpha(*needle)) {
+ const char a[] = { tolower(*needle), toupper(*needle), '\0'};
+ haystack = strpbrk(haystack, a);
strpbrk has a high startup overhead and is slow overall. A basic
while loop checking tolower (haystack[0]) will be faster here.
+ } else {
+ haystack = strchr(haystack, *needle);
+ }
+ if (haystack == NULL || needle[1] == '\0')
+ return (char *)haystack;
This should help a bit in some cases, but searching for the first
character match improves performance the most if you check for
a full match before the expensive initialization of the main algorithm
(similar to what strstr does).
Note that using strchr on a large haystack may actually result in a
slowdown given that the matching algorithms are faster than strchr
on typical inputs (due to being superlinear).
Cheers,
Wilco
next reply other threads:[~2023-09-07 22:14 UTC|newest]
Thread overview: 10+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-09-07 22:14 Wilco Dijkstra [this message]
2023-10-14 8:32 ` James Tirta Halim
2023-10-16 12:59 ` Adhemerval Zanella Netto
2023-10-16 13:52 ` Wilco Dijkstra
2023-10-16 16:56 ` Noah Goldstein
2023-10-17 9:57 ` Wilco Dijkstra
2023-10-14 8:56 ` [PATCH 1/2] " James Tirta Halim
2023-11-28 14:01 ` [PATCH] strcasestr: try to find non-alpha char in NEEDLE James Tirta Halim
2023-12-04 14:44 ` Carlos O'Donell
-- strict thread matches above, loose matches on Subject: below --
2023-09-06 17:42 [PATCH] strcasestr: check if ne[0] is in hs with strchr or strpbrk as does strstr James Tirta Halim
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