Re: [PATCH 1/3] X86: Optimise fls(), ffs() and fls64()

[Avi Kivity]

On 04/15/2010 11:48 AM, David Howells wrote:
> Avi Kivity<avi@xxxxxxxxxx>  wrote:
>
>    
> > Even if Intel processors behave that way, other processors (real and
> > emulated) use those manuals as a specification.  Emulated processors are
> > unlikely to touch an undefined register, but real processors may.
> >
> > (qemu tcg appears not to touch the output)
> >      
> Possibly because the AMD64 spec specifies that the destination will be
> unchanged if the source was 0.
>    

Likely.  But we haven't tested all current and future x86 clones, and 
they may be based off the Intel documentation instead of the AMD 
documentation.

--
I have a truly marvellous patch that fixes the bug which this
signature is too narrow to contain.

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