Messages in this thread |  | | Date | Mon, 11 Dec 2006 08:49:36 +1100 | From | Eyal Lebedinsky <> | Subject | Re: optimalisation for strlcpy (lib/string.c) |
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Folkert van Heusden wrote: > Hi, > > Like the other patch (by that other person), I think it is faster to not > do a strlen first. > E.g. replace this: > ize_t strlcpy(char *dest, const char *src, size_t size) > { > size_t ret = strlen(src); > > if (size) { > size_t len = (ret >= size) ? size - 1 : ret; > memcpy(dest, src, len); > dest[len] = '\0'; > } > return ret; > } > by this: > size_t strlcpy(char *dest, const char *src, size_t size) > { > char *tmp = dest; > > for(;;) > { > *dest = *src; > if (!*src) > break; > > if (--size == 0) > break; > > dest++; > src++; > } > > *dest = 0x00; > > return dest - tmp; > } > patch: > diff -uNrBbd lib/string.c string-new.c > --- lib/string.c 2006-11-04 02:33:58.000000000 +0100 > +++ string-new.c 2006-12-10 22:22:08.000000000 +0100 > @@ -121,14 +121,24 @@ > */ > size_t strlcpy(char *dest, const char *src, size_t size) > { > - size_t ret = strlen(src); > + char *tmp = dest; > > - if (size) { > - size_t len = (ret >= size) ? size - 1 : ret; > - memcpy(dest, src, len); > - dest[len] = '\0'; > + for(;;) > + { > + *dest = *src; > + if (!*src) > + break; > + > + if (--size == 0) > + break; > + > + dest++; > + src++; > } > - return ret; > + > + *dest = 0x00; > + > + return dest - tmp; > } > EXPORT_SYMBOL(strlcpy); > #endif > > > I've tested the speed difference with this: > http://www.vanheusden.com/misc/kernel-strlcpy-opt-test.c > and the speed difference is quite a bit on a P4: 28% faster. > > > Signed-off by: Folkert van Heusden <folkert@vanheusden.com> > > > Folkert van Heusden
The two do not do exactly the same. The first one handles 'size == 0' (should not happen?) safely while the other does not.
-- Eyal Lebedinsky (eyal@eyal.emu.id.au) <http://samba.org/eyal/> attach .zip as .dat - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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