[PATCH v2 3/5] math: Improve fmod

[Wilco Dijkstra]

Hi,

It's these cases where x87 is still faster than the generic version:

> E5-2640          | close-exponents | 39.298   | 22.2742
>
> i7-4510U         | close-exponents | 29.463   | 22.8572

Are these mostly x < y or cases where the exponent difference is just over 11 and
thus we do not use the fast path?

> I am also checking a algorithm change to use simple loop for the normal inputs,
> where integer modulo operation is used instead of inverse multiplication. 

Adding another fast path for a wider range of exponent difference could be faster
than the generic modulo loop. This could do 2 modulo steps and maybe handle
tail zeroes (which I think is what HJ's testcase will benefit from).

For really large exponent differences, the generic modulo code could process 30
or 60 bits per iteration instead of just 11. It's more complex (so would be a separate
patch) but it should help CPUs with relatively high latency multipliers.

Cheers,
Wilco