Re: [PATCH 5/14] i386 / Use early clobber to eliminate rotate indesc

[H. Peter Anvin]

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@xxxxxxxxxxxxxxx
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/