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

[H. Peter Anvin]

Alan Cox wrote:
> On Maw, 2005-08-16 at 17:06 -0700, H. Peter Anvin wrote:
>
> > At least i386 and x86-64 gcc should recognize
> >
> > 	((foo << x) + (foo >> (32-x)))
> >
> > ... as a 32-bit rotate
>
>
> Only for  1 <= x <= 31. For the x = 0 case the code posted is undefined
> and at least in some cases gcc will do "interesting" things as a result
> such as treating >> 32 as >> 0.

True, although I thought gcc considered the above an idiom and would 
generate a rotate instruction.  Perhaps it should be | rather than +.

	-hpa
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