floating point number from crypto.randomBytes() in javascript

问题

How do I convert the array of bytes returned from crypto.randomBytes into a to a floating point number? I'm writing a small replacement for Math.random()

回答1:

Suppose you have a series of bytes randomly selected with uniform distribution over [0, 256). Take seven of those bytes, say a₀, a₁,… a₆. Calculate (((((((a₆ % 32)/32 + a₅)/256 + a₄)/256 + a₃)/256 + a₂)/256 + a₁)/256 + a₀)/256.

Explanation: a₆ % 32 denotes the residue of a₆ modulo 32. This takes five bits of a₆. Then division by 32 “shifts” these bits to the right of the radix point, eight new bits are added, a division by 256 “shifts” right eight bits, and so on until we have 53 bits.

This provides 2⁵³ possible results in [0, 1). It is possible to provide more since the floating-point resolution is finer as values get closer to zero, but then there are problems with uniformity and other issues.

来源：https://stackoverflow.com/questions/15753019/floating-point-number-from-crypto-randombytes-in-javascript