On Mon, Jan 16, 2017 at 11:01:23AM +0100, Stephan Houben wrote:
[...]
> So the following would not be a valid FMA fallback
>
> double bad_fma(double x, double y, double z) {
> return x*y + z;
> }
[...]
> Upshot: if we want to provide a software fallback in the Python code, we
> need to do something slow and complicated like musl does.
I don't know about complicated. I think this is pretty simple:
from fractions import Fraction
def fma(x, y, z):
# Return x*y + z with only a single rounding.
return float(Fraction(x)*Fraction(y) + Fraction(z))
When speed is not the number one priority and accuracy is important,
its hard to beat the fractions module.
--
Steve
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