104 lines
2.5 KiB
JavaScript
104 lines
2.5 KiB
JavaScript
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// A Javascript implementaion of the "Tyche-i" prng algorithm by
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// Samuel Neves and Filipe Araujo.
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// See https://eden.dei.uc.pt/~sneves/pubs/2011-snfa2.pdf
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(function(global, module, define) {
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function XorGen(seed) {
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var me = this, strseed = '';
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// Set up generator function.
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me.next = function() {
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var b = me.b, c = me.c, d = me.d, a = me.a;
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b = (b << 25) ^ (b >>> 7) ^ c;
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c = (c - d) | 0;
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d = (d << 24) ^ (d >>> 8) ^ a;
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a = (a - b) | 0;
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me.b = b = (b << 20) ^ (b >>> 12) ^ c;
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me.c = c = (c - d) | 0;
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me.d = (d << 16) ^ (c >>> 16) ^ a;
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return me.a = (a - b) | 0;
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};
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/* The following is non-inverted tyche, which has better internal
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* bit diffusion, but which is about 25% slower than tyche-i in JS.
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me.next = function() {
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var a = me.a, b = me.b, c = me.c, d = me.d;
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a = (me.a + me.b | 0) >>> 0;
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d = me.d ^ a; d = d << 16 ^ d >>> 16;
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c = me.c + d | 0;
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b = me.b ^ c; b = b << 12 ^ d >>> 20;
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me.a = a = a + b | 0;
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d = d ^ a; me.d = d = d << 8 ^ d >>> 24;
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me.c = c = c + d | 0;
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b = b ^ c;
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return me.b = (b << 7 ^ b >>> 25);
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}
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*/
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me.a = 0;
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me.b = 0;
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me.c = 2654435769 | 0;
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me.d = 1367130551;
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if (seed === Math.floor(seed)) {
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// Integer seed.
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me.a = (seed / 0x100000000) | 0;
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me.b = seed | 0;
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} else {
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// String seed.
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strseed += seed;
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}
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// Mix in string seed, then discard an initial batch of 64 values.
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for (var k = 0; k < strseed.length + 20; k++) {
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me.b ^= strseed.charCodeAt(k) | 0;
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me.next();
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}
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}
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function copy(f, t) {
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t.a = f.a;
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t.b = f.b;
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t.c = f.c;
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t.d = f.d;
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return t;
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};
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function impl(seed, opts) {
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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 (typeof(state) == 'object') 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.tychei = 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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