Messages in this thread | | | Date | Mon, 18 Aug 2003 12:06:39 -0400 | From | Timothy Miller <> | Subject | Re: generic strncpy - off-by-one error |
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Peter Kjellerstedt wrote:
> > For loops 2.867568 5.620561 8.128734 28.286289 > Multi byte fill 2.868031 5.670782 6.312027 11.336015 > > And here are the numbers for my P4: > > For loops 3.060262 5.927378 8.796814 30.659818 > Multi byte fill 3.126607 5.898459 7.096685 13.135379 > > So there is no doubt that the multi byte version is a clear > winner (which was expected, I suppose).
Cool! Hey, is this just an exercise, or are we actually going to use this? I would be very happy to have something I contributed to put into the kernel. :)
> > Here is the code that I used: > > char *strncpy(char *dest, const char *src, size_t count) > { > char *tmp = dest; > > while (count && *src) { > *tmp++ = *src++; > count--; > } > > if (count) {
Good idea... bad to do so many checks if count is zero. On the other hand, if count is rarely zero, then it's a loss. Maybe benchmark with and without?
> size_t count2; > > while (count & (sizeof(long) - 1)) { > *tmp++ = '\0'; > count--; > } > > count2 = count / sizeof(long);
I know that a good compiler should migrate code to help the CPU pipeline, but how about moving this "count2 = " line up to before the first fill loop. See if that helps any. Always good to precompute well in advance.
> while (count2) { > *((long *)tmp)++ = '\0'; > count2--; > } > > count &= (sizeof(long) - 1);
And move this to before the middle fill loop.
> while (count) { > *tmp++ = '\0'; > count--; > } > } > > return dest; > } > > //Peter > >
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