Re: Optimize numeric multiplication for one and two base-NBASE digit multiplicands.

On Fri, 5 Jul 2024 at 12:56, Joel Jacobson <joel(at)compiler(dot)org> wrote:
>
> Interesting you got so bad bench results for v6-mul_var_int64.patch
> for var1ndigits=4, that patch is actually the winner on AMD Ryzen 9 7950X3D.

Interesting.

> On Intel Core i9-14900K the winner is v6-optimize-numeric-mul_var-small-var1-arbitrary-var2.patch.

That must be random noise, since
v6-optimize-numeric-mul_var-small-var1-arbitrary-var2.patch doesn't
invoke mul_var_small() for 4-digit inputs.

> On Apple M3 Max, HEAD is the winner.

Importantly, mul_var_int64() is around 1.25x slower there, and it was
even worse on my machine.

Attached is a v7 mul_var_small() patch adding 4-digit support. For me,
this gives a nice speedup:

SELECT SUM(var1*var2) FROM bench_mul_var_var1ndigits_4;
Time: 5617.150 ms (00:05.617) -- HEAD
Time: 8203.081 ms (00:08.203) -- v6-mul_var_int64.patch
Time: 4750.212 ms (00:04.750) -- v7-mul_var_small.patch

The other advantage, of course, is that it doesn't require 128-bit
integer support.

Regards,
Dean