81 lines
1.8 KiB
JavaScript
Executable File
81 lines
1.8 KiB
JavaScript
Executable File
/**
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* Pseudo random number generator
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* using the xorshift32 method.
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*/
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export class Xorshift32 {
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/* @type {number} */
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state;
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/** @param {number} seed */
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constructor(seed) {
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this.state = seed | 0;
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}
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/** @protected Shuffle the internal state. */
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shuffle() {
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//
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// Run the actual xorshift32 algorithm
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let x = this.state;
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x ^= x << 13;
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x ^= x >>> 17;
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x ^= x << 5;
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x = (x >>> 0) / 4294967296;
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this.state = x;
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}
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/**
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* Get a random number and shuffle the internal state.
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* @returns {number} a pseudo-random positive integer.
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*/
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get() {
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this.shuffle();
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return this.state;
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}
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/** @param {number} x @returns {number} a positive integer lower than x */
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lowerThan(x) {
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return this.get() % x;
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}
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/** @param {number} x @reurns {number} a positive integer lower than or equal to x */
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lowerThanOrEqual(x) {
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return this.get() % (x + 1);
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}
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/**
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* @param {<T>[]} arr
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*
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* @return {<T>}
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*/
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randomElement(arr) {
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const idx = this.lowerThan(arr.length);
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return arr[idx];
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}
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/**
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* @param {...<T>} args
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* @returns {<T>}
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*/
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oneOf(...args) {
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const idx = this.lowerThan(args.length);
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return args[idx];
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}
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/**
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* @param {number} lowerThanOrEqual a positive integer
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* @param {number} greaterThanOrEqual a positive integer greater than lowerThanOrEqual
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* @returns {number} a pseudo-random integer
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*/
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within(greaterThanOrEqual, lowerThanOrEqual) {
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const range = lowerThanOrEqual - greaterThanOrEqual;
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const num = this.lowerThanOrEqual(range);
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return num + greaterThanOrEqual;
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}
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}
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