The Rand structure

The Rand structure provides a simple random number generator as described in Larry Paulson in ML for the Working Programmer (pp. 170-171). The original algorithm was recommended by Park and Miller in Random number generators: good ones are hard to find, CACM 1988 (pp 1192-1201) with modifications described in CACM 1993 (pp. 105-110).

Note: it is recommended that one use the Random structure when the quality of the generated numbers is at all important. The main advantages of this implementation is that it is functional (the generators provided by the Random structure are imperative) and it is fast.

Synopsis

structure Rand

Interface

type rand = Word.word

val randMin : rand
val randMax : rand

val random : rand -> rand

val mkRandom : rand -> unit -> rand

val norm : rand -> real

val range : (int * int) -> rand -> int

Description

type rand = Word.word

The "state" of the generator, which is just a single word.

val randMin : rand

The minimum allowed value for the state.

val randMax : rand

The maximum allowed value for the state.

val random : rand -> rand

random seed returns a pseudo-random value in the range [randMin .. randMax]. Iteratively using the value returned by random as the next seed will produce a sequence of pseudo-random numbers.

val mkRandom : rand -> unit -> rand

something (* Given seed, return function generating a sequence of

  • random numbers randMin ⇐ v ⇐ randMax *)

val norm : rand -> real

norm rand maps the random number in the range [randMin .. randMax] to the real interval (0..1).

val range : (int * int) -> rand -> int

range (lo, hi) rand maps the random number in the range [randMin .. randMax] to the interval [lo..hi]. This function will raise the Fail exception if hi < lo.

Bugs

This implementation needs to be updated for 64-bit systems.