This is awesome and the first precedent I've ever seen for a standard library doing the right thing on rand floats. Big kudos to the zig people and thanks for brightening my day!

Oh, cute. It looks like they ever-so-slightly overweight the probability of values whose mantissa is entirely zeroes though. For example, the probability of hitting exactly 0.5 should be 2^-54 + 2^-55, whereas zig looks to give it 2^-54 + 2^-54.