Function fast 

pub fn fast(bits: impl FnMut() -> u64) -> f64

Port of uniformbinary64_fast: a correctly rounded (to nearest) uniform real in [0 . . 1], branching on the 2⁻⁶⁴-probability zero-m event.

Consumes two 64-bit words, plus a third with probability 2⁻⁶⁴.