cvs commit: src/lib/libc/string strcspn.c strspn.c src/sys/libkern strspn.c

Olivier Houchard cognet at ci0.org
Sat Apr 2 14:58:32 PST 2005


On Sat, Apr 02, 2005 at 01:57:06PM -0500, David Schultz wrote:
> On Sat, Apr 02, 2005, David Schultz wrote:
> > das         2005-04-02 18:52:44 UTC
> > 
> >   FreeBSD src repository
> > 
> >   Modified files:
> >     lib/libc/string      strcspn.c strspn.c 
> >     sys/libkern          strspn.c 
> >   Log:
> >   Replace the current strspn() and strcspn() with significantly faster
> >   implementations inspired by the ones in DragonFly.  Unlike the
> >   DragonFly versions, these have a small data cache footprint, and my
> >   tests show that they're never slower than the old code except when the
> >   charset or the span is 0 or 1 characters.  This implementation is
> >   generally faster than DragonFly until either the charset or the span
> >   gets in the ballpark of 32 to 64 characters.
> 
> BTW, anyone know a good reason why we have optimized string
> functions (e.g. strcmp(), strcpy()) in libc, but not in libkern?
> In testing strcmp(s, s), I found that the libc version on i386 is
> 11% faster when s has length 1 and 4% faster when s has length 400.
> 
> The kernel has many consumers of these functions, but maybe their
> performance is irrelevant in the grand scheme of things.
> Certainly things like bcopy and bswap are more important...

For what it worth, I noticed a small performance increase when using
optimized versions of strcmp and strncmp in libkern on arm, so it might 
be a good idea.

Olivier


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