[Top][All Lists]
[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]
Re: [Qemu-devel] [PATCH] target-arm: fix SMMLA/SMMLS instructions
From: |
Aurelien Jarno |
Subject: |
Re: [Qemu-devel] [PATCH] target-arm: fix SMMLA/SMMLS instructions |
Date: |
Thu, 6 Jan 2011 18:24:57 +0100 |
User-agent: |
Mutt/1.5.18 (2008-05-17) |
On Thu, Jan 06, 2011 at 03:54:46PM +0000, Peter Maydell wrote:
> On 6 January 2011 15:50, Aurelien Jarno <address@hidden> wrote:
> > On Wed, Jan 05, 2011 at 11:15:15AM +0000, Peter Maydell wrote:
>
> >> Isn't this adding b to the msw of a, rather than the other
> >> way round as the comment claims?
> >
> > I think the comment is actually wrong in both way, as a shift is
> > applied, and thus lsw of b is used as the msw in the addition.
>
> We add the whole of b, not the lsw of b, because it's only
> 32 bits to start with (ie "lsw of b" is a longwinded way of
> saying "b").
>
> > What about "Add a to (b << 32). Mark inputs as dead."?
>
> To me "Add x to y" means "y = y + x". In this case that would
> mean "(b << 32) = (b << 32) + a", which is nonsensical.
> "Add (b << 32) to a" or equivalently "add b to the msw of a"
> makes more sense to me.
>
Ok, will use that in the next version.
For the subtraction, how would you say a = (b << 32) - a ?
--
Aurelien Jarno GPG: 1024D/F1BCDB73
address@hidden http://www.aurel32.net