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Subject: Re: [PATCH 5/14] i386 / Use early clobber to eliminate rotate in
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From: Alan Cox <alan@lxorguk.ukuu.org.uk>
To: "H. Peter Anvin" <hpa@zytor.com>
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Date: Wed, 17 Aug 2005 15:22:22 +0100
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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.

Alan