simple-squiggle/node_modules/seedrandom/lib/tychei.js

104 lines
2.5 KiB
JavaScript

// A Javascript implementaion of the "Tyche-i" prng algorithm by
// Samuel Neves and Filipe Araujo.
// See https://eden.dei.uc.pt/~sneves/pubs/2011-snfa2.pdf
(function(global, module, define) {
function XorGen(seed) {
var me = this, strseed = '';
// Set up generator function.
me.next = function() {
var b = me.b, c = me.c, d = me.d, a = me.a;
b = (b << 25) ^ (b >>> 7) ^ c;
c = (c - d) | 0;
d = (d << 24) ^ (d >>> 8) ^ a;
a = (a - b) | 0;
me.b = b = (b << 20) ^ (b >>> 12) ^ c;
me.c = c = (c - d) | 0;
me.d = (d << 16) ^ (c >>> 16) ^ a;
return me.a = (a - b) | 0;
};
/* The following is non-inverted tyche, which has better internal
* bit diffusion, but which is about 25% slower than tyche-i in JS.
me.next = function() {
var a = me.a, b = me.b, c = me.c, d = me.d;
a = (me.a + me.b | 0) >>> 0;
d = me.d ^ a; d = d << 16 ^ d >>> 16;
c = me.c + d | 0;
b = me.b ^ c; b = b << 12 ^ d >>> 20;
me.a = a = a + b | 0;
d = d ^ a; me.d = d = d << 8 ^ d >>> 24;
me.c = c = c + d | 0;
b = b ^ c;
return me.b = (b << 7 ^ b >>> 25);
}
*/
me.a = 0;
me.b = 0;
me.c = 2654435769 | 0;
me.d = 1367130551;
if (seed === Math.floor(seed)) {
// Integer seed.
me.a = (seed / 0x100000000) | 0;
me.b = seed | 0;
} else {
// String seed.
strseed += seed;
}
// Mix in string seed, then discard an initial batch of 64 values.
for (var k = 0; k < strseed.length + 20; k++) {
me.b ^= strseed.charCodeAt(k) | 0;
me.next();
}
}
function copy(f, t) {
t.a = f.a;
t.b = f.b;
t.c = f.c;
t.d = f.d;
return t;
};
function impl(seed, opts) {
var xg = new XorGen(seed),
state = opts && opts.state,
prng = function() { return (xg.next() >>> 0) / 0x100000000; };
prng.double = function() {
do {
var top = xg.next() >>> 11,
bot = (xg.next() >>> 0) / 0x100000000,
result = (top + bot) / (1 << 21);
} while (result === 0);
return result;
};
prng.int32 = xg.next;
prng.quick = prng;
if (state) {
if (typeof(state) == 'object') copy(state, xg);
prng.state = function() { return copy(xg, {}); }
}
return prng;
}
if (module && module.exports) {
module.exports = impl;
} else if (define && define.amd) {
define(function() { return impl; });
} else {
this.tychei = impl;
}
})(
this,
(typeof module) == 'object' && module, // present in node.js
(typeof define) == 'function' && define // present with an AMD loader
);