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// Based on: https://github.com/dubzzz/pure-rand/blob/5da623a4eebf47f01c5b87c43c9fb4d43ad949bd/src/generator/MersenneTwister.ts
const N = 624;
const M = 397;
const R = 31;
const A = 0x9908b0df;
const F = 1812433253;
const U = 11;
const S = 7;
const B = 0x9d2c5680;
const T = 15;
const C = 0xefc60000;
const L = 18;
const MASK_LOWER = 2 ** R - 1;
const MASK_UPPER = 2 ** R;
const HIGH_MULTIPLIER_53 = 67108864.0;
const FLOATIFY_32 = 1.0 / 4294967296.0;
const FLOATIFY_53 = 1.0 / 9007199254740992.0;
const { imul, trunc } = Math;
/**
* Generates the random state from the given number or array.
*
* @param seed The seed to generate the random state from.
*/
function seedFrom(seed: number | number[]): number[] {
return typeof seed === 'number' ? numberSeeded(seed) : arraySeeded(seed);
}
/**
* Generates the random state from the given number.
*
* @param seed The seed to generate the random state from.
*/
function numberSeeded(seed: number): number[] {
const out = Array.from<number>({ length: N });
out[0] = seed;
for (let idx = 1; idx !== N; ++idx) {
const xored = out[idx - 1] ^ (out[idx - 1] >>> 30);
out[idx] = trunc(imul(F, xored) + idx);
}
return out;
}
/**
* Generates the random state from the given array.
*
* @param seed The seed to generate the random state from.
*/
function arraySeeded(seed: number[]): number[] {
const out = numberSeeded(19650218);
let idxOut = 1;
let idxSeed = 0;
for (let iteration = Math.max(N, seed.length); iteration !== 0; --iteration) {
const xored = out[idxOut - 1] ^ (out[idxOut - 1] >>> 30);
out[idxOut] = trunc(
(out[idxOut] ^ imul(xored, 1664525)) + seed[idxSeed] + idxSeed
);
idxOut++;
idxSeed++;
if (idxOut >= N) {
out[0] = out[N - 1];
idxOut = 1;
}
if (idxSeed >= seed.length) {
idxSeed = 0;
}
}
for (let iteration = N - 1; iteration !== 0; iteration--) {
out[idxOut] = trunc(
(out[idxOut] ^
imul(out[idxOut - 1] ^ (out[idxOut - 1] >>> 30), 1566083941)) -
idxOut
);
idxOut++;
if (idxOut >= N) {
out[0] = out[N - 1];
idxOut = 1;
}
}
out[0] = 0x80000000;
return out;
}
/**
* Twists the given randomness states.
*
* @param states The randomness states to twist.
*
* @returns The given states.
*/
function twist(states: number[]): number[] {
for (let idx = 0; idx !== N - M; ++idx) {
const y = (states[idx] & MASK_UPPER) + (states[idx + 1] & MASK_LOWER);
states[idx] = states[idx + M] ^ (y >>> 1) ^ (-(y & 1) & A);
}
for (let idx = N - M; idx !== N - 1; ++idx) {
const y = (states[idx] & MASK_UPPER) + (states[idx + 1] & MASK_LOWER);
states[idx] = states[idx + M - N] ^ (y >>> 1) ^ (-(y & 1) & A);
}
const y = (states[N - 1] & MASK_UPPER) + (states[0] & MASK_LOWER);
states[N - 1] = states[M - 1] ^ (y >>> 1) ^ (-(y & 1) & A);
return states;
}
/**
* Mersenne Twister based random number generator.
*/
export class MersenneTwister19937 {
/**
* Creates a new Mersenne Twister random number generator based on the given seed.
*
* @param seed The seed to generate the random state from. Defaults to a random seed.
*/
constructor(seed?: number | number[]);
/**
* Creates a new Mersenne Twister random number generator based on the given seed.
*
* @param seed The seed to generate the random state from. Defaults to a random seed.
* @param states The states to use, must be an array of 624 32-bit integers.
* @param index The index to use, must be a number between 0 and 623.
*/
constructor(
seed: number | number[] = Math.random() * Number.MAX_SAFE_INTEGER,
private states: number[] = twist(seedFrom(seed)),
private index: number = 0
) {}
/**
* Generates the next 32-bit unsigned integer.
*/
nextU32(): number {
let y = this.states[this.index];
y ^= this.states[this.index] >>> U;
y ^= (y << S) & B;
y ^= (y << T) & C;
y ^= y >>> L;
if (++this.index >= N) {
this.states = twist(this.states);
this.index = 0;
}
return y >>> 0;
}
/**
* Generates the next 32-bit float.
*/
nextF32(): number {
return this.nextU32() * FLOATIFY_32;
}
/**
* Generates the next 53-bit unsigned integer.
*/
nextU53(): number {
const high = this.nextU32() >>> 5;
const low = this.nextU32() >>> 6;
return high * HIGH_MULTIPLIER_53 + low;
}
/**
* Generates the next 53-bit float.
*/
nextF53(): number {
return this.nextU53() * FLOATIFY_53;
}
/**
* Sets the seed of the random number generator.
*
* @param seed The seed to use.
*/
seed(seed: number | number[]): void {
this.states = twist(seedFrom(seed));
this.index = 0;
}
}
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