Faster uniform() in [0.0 - 1.0(

[tn]

bearophile Wrote:

> Don:
> 
> > Since the probability of actually generating a 
> > zero is 1e-4000, it shouldn't affect the speed at all <g>.
> 
> If bits in double have the same probability then I think there is a much higher probability to hit a zero, about 1 in 2^^63, and I'm not counting NaNs (but it's low enough to not change the substance of what you have said).

For uniform distribution different bit combinations should have different probabilities because floating point numbers have more representable values close to zero. So for doubles the probability should be about 1e-300 and for reals about 1e-4900.

But because uniform by default seems to use a 32 bit integer random number generator, the probability is actually 2^^-32. And that is actually verified: I generated 10 * 2^^32 samples of uniform!"[]"(0.0, 1.0) and got 16 zeros which is close enough to expected 10.

Of course 2^^-32 is still small enough to have no performance penalty in practise.

-- tn