lkml.org 
[lkml]   [2005]   [Aug]   [16]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: [PATCH 5/14] i386 / Use early clobber to eliminate rotate in desc
Zachary Amsden wrote:
>
> This one in particular is non-optimal looking from C because the
> compiler misses the potential for rotation. But, composing into
> temporaries and then issuing two writes to memory instead of multiple
> writes within the same word could actually get you a better cycle count,
> and that is something GCC just might be able to do :)
>

At least i386 and x86-64 gcc should recognize

((foo << x) + (foo >> (32-x)))

... as a 32-bit rotate; similar for 8-, 16- and 64-bit rotates of
appropriate sized items. Also, it seems it could just be an inline
function instead of a macro.

-hpa

-
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: 2005-08-17 02:10    [W:0.040 / U:0.144 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site