The Random structure

The Random structure implements a random number generator using the Mersenne Twister algorithm. The implementation is specialized to the native word size.

Note that prior to 2023.1 (and 110.99.4), this structure was implemented using a subtract-with-borrow algorithm.

Synopsis

structure Random :> RANDOM

Interface

type rand

val rand : (int * int) -> rand

val fromList : NativeWord.word list -> rand

val toBytes : rand -> Word8Vector.vector
val fromBytes : Word8Vector.vector -> rand

val toString : rand -> string
val fromString : string -> rand

val randNativeInt : rand -> NativeInt.int

val randNativeWord : rand -> NativeWord.word

val randInt : rand -> int

val randWord : rand -> int

val randNat : rand -> int

val randReal : rand -> real

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

Description

type rand: Represents the internal state of a random number generator.
val rand : (int * int) -> rand: rand (n1, n2) creates a random number generator from the initial seed specified by the pair (n1, n2). This function is kept for backward compatibility with the old implementation, but it is recommended that one use the fromList function in new code.
val fromList : NativeWord.word list -> rand: creates a random number generator from the given list of initial seeds.
val toBytes : rand -> Word8Vector.vector: toBytes rand returns a byte vector representing the current state of the generator.
val fromBytes : Word8Vector.vector -> rand: fromBytes bv creates a generator with the initial state that was encoded in the byte vector bv. This expression will raise Fail exception if the byte vector is invalid.
val toString : rand -> string: toString rand returns a string representing the random-number-generator state rand. This string is a Base64 encoding of the result of toBytes rand.
val fromString : string -> rand: fromString s returns the random-number-generator encoded as the string s (presumably generated by toString). This expression will raise Fail exception if the string s does not have the proper form.
val randNativeWord : rand -> NativeWord.word: randNativeWord rand generates a uniform random number in the range \([0 .. 2^k-1\)], where \(k\) is the host platform’s native word size (e.g., 32 or 64).
val randNativeInt : rand -> NativeInt.int: randNativeInt rand generates a random word a uniform distribution in the range \([0 .. 2^{k-1}-1\)], where \(k\) is the host platform’s native word size (e.g., 32 or 64).
val randInt : rand -> int: randInt rand generates a random integer with a uniform distribution in the range \([-2^{k-1} .. 2^{k-1}-1\)], where \(k\) is the host platform’s default word size (e.g., 31 or 63).
val randWord : rand -> word: randWord rand generates a random word with a uniform distribution in the range \([0 .. 2^k-1\)], where \(k\) is the host platform’s default word size (e.g., 31 or 63).
val randNat : rand -> int: randNat rand generates a random integer with a uniform distribution in the range \([0 .. 2^{k-1}-1\)], where \(k\) is the host platform’s default word size (e.g., 31 or 63).
val randReal : rand -> real: randReal rand generates a random real number in the range [0..1).
val randRange : (int * int) -> rand -> int: randRange (lo, hi) rand generates a random number in the [lo..hi]. This function will raise the Fail exception if hi < lo.

Synopsis

Interface

Description

See Also