Re: Interesting pentium-memcpy results

Ingo Molnar (
Tue, 29 Jul 1997 16:47:31 +0200 (MET DST)

On Tue, 29 Jul 1997, Robert L Krawitz wrote:

> the 'soft' routine is not complete, eg. it does not save FPU flags .. but
> it saves the 'main bulk', the 80 bit FPU registers. Maybe there are other
> things too to save? Everything that might be affected by those fildl and
> fistl instructions should be saved.
> There's also the issue of making certain that the FPU is in a sane
> state. If the FPU's in a weird state, it's possible that fildq/fistpq
> might not do the right thing, although I don't know that for certain.

another speedup for the soft method: to analyse 'stacktop', and do less
stores/restores if it's less than 8. Usually it's 0 or 1?

FPU states are clearly defined. I think we cant even mess up NaN's with
'fldt' 'fstpt'? Not sure about the per-register 'tag' bit.

-- mingo