lkml.org 
[lkml]   [2005]   [Jul]   [28]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
SubjectRe: [PATCH] speed up on find_first_bit for i386 (let compiler do the work)
From
Date
On Thu, 2005-07-28 at 17:34 +0100, Maciej W. Rozycki wrote:

> Since you're considering GCC-generated code for ffs(), ffz() and friends,
> how about trying __builtin_ffs(), __builtin_clz() and __builtin_ctz() as
> apropriate? Reasonably recent GCC may actually be good enough to use the
> fastest code depending on the processor submodel selected.

I can change the find_first_bit to use __builtin_ffs, but how would you
implement the ffz? The clz and ctz only count the number of leading or
trailing zeros respectively, it doesn't find the first zero. Of course a
__builtin_ctz(~x) would but this might take longer than what we already
have. I'll go ahead and try it and see. But I still don't have a
decent benchmark on this. I'll start looking into the kernel and see how
it's used, and see if I can find a proper benchmark.

-- Steve


-
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/

\
 
 \ /
  Last update: 2005-07-28 19:04    [W:0.503 / U:0.048 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site