Re: [Qemu-devel] [Qemu-ppc] [PATCH 1/6] target-ppc: add vmul10[u, eu, cu, ecu]q instructions

[David Gibson]

On Wed, Sep 28, 2016 at 09:00:51PM -0700, Richard Henderson wrote:
> On 09/28/2016 07:07 PM, David Gibson wrote:
> > > +    tcg_gen_mulu2_i64(t0, t1, cpu_avrl[rA(ctx->opcode)], val);          \
> > 
> > Do you really want to be using an actual mul op, rather than (in << 3)
> > + (in << 1)?  Obviously working out al the carries correctly will be a
> > bit fiddly.
> 
> I think it's fine.  Modern hardware will do the double-word multiply in 3-5
> cycles, which is probably equal to what we could do by hand with
> shifts.

Fair enough.  And it will make for less dicking around with the carry
in and carry out.

-- 
David Gibson                    | I'll have my music baroque, and my code
david AT gibson.dropbear.id.au  | minimalist, thank you.  NOT _the_ _other_
                                | _way_ _around_!
http://www.ozlabs.org/~dgibson

signature.asc
Description: PGP signature