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

[Richard Henderson]

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.


r~