Re: [PATCH 6/8] softfloat: Implement float128_muladd

[Richard Henderson]

On 9/24/20 12:56 AM, David Hildenbrand wrote:
> I do wonder if a type for Int256 would make sense - instead of > manually 
> passing these arrays.

I could do that.  It does name better, I suppose, in passing.  So long as
you're happy having the guts of the type be public, and not wrapping everything
like we do for Int128...

Either is better than the softfloat style, which would pass 12 arguments to
these helpers... ;-)

>> +static void shortShift256Left(uint64_t p[4], unsigned count)
>> +{
>> +    int negcount = -count & 63;
> 
> That's the same as "64 - count", right? (which I find easier to get)

In this case, yes.

Of course, more hosts have a "neg" instruction than they do a
"subtract-from-immediate" instruction.  When the shift instruction only
examines the low N bits, the "& 63" is optimized away, so this can result in 1
fewer instruction in the end.

Which is why I almost always use this form, and it's already all over the code
inherited from upstream.

> Wow, that's a beast :)

But not much worse than muladd_floats(), I'm pleased to say.


r~