Re: [Qemu-devel] [PATCH] target-arm: fix SMMLA/SMMLS instructions

[Peter Maydell]

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.

-- PMM