98 lines
2.4 KiB
JavaScript
98 lines
2.4 KiB
JavaScript
// A Javascript implementaion of the "xorshift7" algorithm by
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// François Panneton and Pierre L'ecuyer:
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// "On the Xorgshift Random Number Generators"
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// http://saluc.engr.uconn.edu/refs/crypto/rng/panneton05onthexorshift.pdf
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(function(global, module, define) {
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function XorGen(seed) {
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var me = this;
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// Set up generator function.
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me.next = function() {
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// Update xor generator.
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var X = me.x, i = me.i, t, v, w;
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t = X[i]; t ^= (t >>> 7); v = t ^ (t << 24);
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t = X[(i + 1) & 7]; v ^= t ^ (t >>> 10);
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t = X[(i + 3) & 7]; v ^= t ^ (t >>> 3);
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t = X[(i + 4) & 7]; v ^= t ^ (t << 7);
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t = X[(i + 7) & 7]; t = t ^ (t << 13); v ^= t ^ (t << 9);
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X[i] = v;
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me.i = (i + 1) & 7;
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return v;
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};
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function init(me, seed) {
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var j, w, X = [];
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if (seed === (seed | 0)) {
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// Seed state array using a 32-bit integer.
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w = X[0] = seed;
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} else {
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// Seed state using a string.
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seed = '' + seed;
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for (j = 0; j < seed.length; ++j) {
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X[j & 7] = (X[j & 7] << 15) ^
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(seed.charCodeAt(j) + X[(j + 1) & 7] << 13);
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}
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}
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// Enforce an array length of 8, not all zeroes.
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while (X.length < 8) X.push(0);
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for (j = 0; j < 8 && X[j] === 0; ++j);
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if (j == 8) w = X[7] = -1; else w = X[j];
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me.x = X;
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me.i = 0;
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// Discard an initial 256 values.
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for (j = 256; j > 0; --j) {
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me.next();
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}
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}
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init(me, seed);
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}
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function copy(f, t) {
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t.x = f.x.slice();
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t.i = f.i;
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return t;
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}
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function impl(seed, opts) {
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if (seed == null) seed = +(new Date);
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var xg = new XorGen(seed),
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state = opts && opts.state,
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prng = function() { return (xg.next() >>> 0) / 0x100000000; };
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prng.double = function() {
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do {
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var top = xg.next() >>> 11,
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bot = (xg.next() >>> 0) / 0x100000000,
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result = (top + bot) / (1 << 21);
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} while (result === 0);
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return result;
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};
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prng.int32 = xg.next;
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prng.quick = prng;
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if (state) {
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if (state.x) copy(state, xg);
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prng.state = function() { return copy(xg, {}); }
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}
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return prng;
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}
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if (module && module.exports) {
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module.exports = impl;
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} else if (define && define.amd) {
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define(function() { return impl; });
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} else {
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this.xorshift7 = impl;
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}
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})(
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this,
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(typeof module) == 'object' && module, // present in node.js
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(typeof define) == 'function' && define // present with an AMD loader
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);
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