[erlang-questions] [ANN] Erlang UUID

[Richard O'Keefe]

On 3/03/2012, at 1:32 PM, Michael Truog wrote:
> If you use this implementation, then it would provide 408 bits of randomness, uniformly distributed.

I don't see how it can.  Just because all the numbers are in a given range does not mean that
all the numbers in that range are possible.  The Wichmann-Hill generator has a state with
4 31-bit numbers, meaning that you can't possibly get more than 124 bits out of it.  If you
really get more, you have a different algorithm.

Using 64-bit integer arithmetic, the algorithm looks like

	a = (a * 11600LL) % 2147483579;
	b = (b * 47003LL) % 2147483543;
	c = (c * 23000LL) % 2147483423;
	d = (d * 33000LL) % 2147483123;
	w = a/2147483579.0 + b/2147483543.0
	  + c/2147483423.0 + d/2147483123.0;
	if (w >= 2.0) w -= 2.0;
	if (w >= 1.0) w -= 1.0;
	return w;