343 lines
13 KiB
JavaScript
Executable File
343 lines
13 KiB
JavaScript
Executable File
// seedrandom.js version 2.3.3
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// Author: David Bau
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// Date: 2014 Feb 4
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//
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// Defines a method Math.seedrandom() that, when called, substitutes
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// an explicitly seeded RC4-based algorithm for Math.random(). Also
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// supports automatic seeding from local or network sources of entropy.
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// Can be used as a node.js or AMD module. Can be called with "new"
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// to create a local PRNG without changing Math.random.
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//
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// Basic usage:
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//
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// <script src=http://davidbau.com/encode/seedrandom.min.js></script>
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//
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// Math.seedrandom('yay.'); // Sets Math.random to a function that is
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// // initialized using the given explicit seed.
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//
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// Math.seedrandom(); // Sets Math.random to a function that is
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// // seeded using the current time, dom state,
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// // and other accumulated local entropy.
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// // The generated seed string is returned.
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//
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// Math.seedrandom('yowza.', true);
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// // Seeds using the given explicit seed mixed
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// // together with accumulated entropy.
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//
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// <script src="https://jsonlib.appspot.com/urandom?callback=Math.seedrandom">
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// </script> <!-- Seeds using urandom bits from a server. -->
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//
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// Math.seedrandom("hello."); // Behavior is the same everywhere:
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// document.write(Math.random()); // Always 0.9282578795792454
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// document.write(Math.random()); // Always 0.3752569768646784
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//
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// Math.seedrandom can be used as a constructor to return a seeded PRNG
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// that is independent of Math.random:
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//
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// var myrng = new Math.seedrandom('yay.');
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// var n = myrng(); // Using "new" creates a local prng without
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// // altering Math.random.
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//
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// When used as a module, seedrandom is a function that returns a seeded
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// PRNG instance without altering Math.random:
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//
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// // With node.js (after "npm install seedrandom"):
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// var seedrandom = require('seedrandom');
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// var rng = seedrandom('hello.');
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// console.log(rng()); // always 0.9282578795792454
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//
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// // With require.js or other AMD loader:
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// require(['seedrandom'], function(seedrandom) {
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// var rng = seedrandom('hello.');
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// console.log(rng()); // always 0.9282578795792454
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// });
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//
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// More examples:
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//
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// var seed = Math.seedrandom(); // Use prng with an automatic seed.
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// document.write(Math.random()); // Pretty much unpredictable x.
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//
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// var rng = new Math.seedrandom(seed); // A new prng with the same seed.
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// document.write(rng()); // Repeat the 'unpredictable' x.
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//
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// function reseed(event, count) { // Define a custom entropy collector.
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// var t = [];
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// function w(e) {
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// t.push([e.pageX, e.pageY, +new Date]);
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// if (t.length < count) { return; }
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// document.removeEventListener(event, w);
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// Math.seedrandom(t, true); // Mix in any previous entropy.
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// }
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// document.addEventListener(event, w);
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// }
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// reseed('mousemove', 100); // Reseed after 100 mouse moves.
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//
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// The callback third arg can be used to get both the prng and the seed.
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// The following returns both an autoseeded prng and the seed as an object,
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// without mutating Math.random:
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//
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// var obj = Math.seedrandom(null, false, function(prng, seed) {
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// return { random: prng, seed: seed };
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// });
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//
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// Version notes:
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//
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// The random number sequence is the same as version 1.0 for string seeds.
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// * Version 2.0 changed the sequence for non-string seeds.
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// * Version 2.1 speeds seeding and uses window.crypto to autoseed if present.
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// * Version 2.2 alters non-crypto autoseeding to sweep up entropy from plugins.
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// * Version 2.3 adds support for "new", module loading, and a null seed arg.
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// * Version 2.3.1 adds a build environment, module packaging, and tests.
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// * Version 2.3.3 fixes bugs on IE8, and switches to MIT license.
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//
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// The standard ARC4 key scheduler cycles short keys, which means that
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// seedrandom('ab') is equivalent to seedrandom('abab') and 'ababab'.
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// Therefore it is a good idea to add a terminator to avoid trivial
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// equivalences on short string seeds, e.g., Math.seedrandom(str + '\0').
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// Starting with version 2.0, a terminator is added automatically for
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// non-string seeds, so seeding with the number 111 is the same as seeding
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// with '111\0'.
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//
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// When seedrandom() is called with zero args or a null seed, it uses a
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// seed drawn from the browser crypto object if present. If there is no
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// crypto support, seedrandom() uses the current time, the native rng,
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// and a walk of several DOM objects to collect a few bits of entropy.
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//
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// Each time the one- or two-argument forms of seedrandom are called,
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// entropy from the passed seed is accumulated in a pool to help generate
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// future seeds for the zero- and two-argument forms of seedrandom.
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//
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// On speed - This javascript implementation of Math.random() is several
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// times slower than the built-in Math.random() because it is not native
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// code, but that is typically fast enough. Some details (timings on
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// Chrome 25 on a 2010 vintage macbook):
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//
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// seeded Math.random() - avg less than 0.0002 milliseconds per call
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// seedrandom('explicit.') - avg less than 0.2 milliseconds per call
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// seedrandom('explicit.', true) - avg less than 0.2 milliseconds per call
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// seedrandom() with crypto - avg less than 0.2 milliseconds per call
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//
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// Autoseeding without crypto is somewhat slower, about 20-30 milliseconds on
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// a 2012 windows 7 1.5ghz i5 laptop, as seen on Firefox 19, IE 10, and Opera.
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// Seeded rng calls themselves are fast across these browsers, with slowest
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// numbers on Opera at about 0.0005 ms per seeded Math.random().
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//
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// LICENSE (BSD):
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//
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// Copyright 2013 David Bau, all rights reserved.
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//
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// Redistribution and use in source and binary forms, with or without
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// modification, are permitted provided that the following conditions are met:
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//
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// 1. Redistributions of source code must retain the above copyright
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// notice, this list of conditions and the following disclaimer.
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//
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// 2. Redistributions in binary form must reproduce the above copyright
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// notice, this list of conditions and the following disclaimer in the
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// documentation and/or other materials provided with the distribution.
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//
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// 3. Neither the name of this module nor the names of its contributors may
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// be used to endorse or promote products derived from this software
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// without specific prior written permission.
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//
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// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
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// "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
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// LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
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// A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
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// OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
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// SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
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// LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
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// DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
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// THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
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// (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
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// OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
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//
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/**
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* All code is in an anonymous closure to keep the global namespace clean.
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*/
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(function (
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global, pool, math, width, chunks, digits, module, define, rngname) {
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//
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// The following constants are related to IEEE 754 limits.
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//
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var startdenom = math.pow(width, chunks),
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significance = math.pow(2, digits),
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overflow = significance * 2,
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mask = width - 1,
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//
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// seedrandom()
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// This is the seedrandom function described above.
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//
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impl = math['seed' + rngname] = function(seed, use_entropy, callback) {
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var key = [];
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// Flatten the seed string or build one from local entropy if needed.
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var shortseed = mixkey(flatten(
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use_entropy ? [seed, tostring(pool)] :
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(seed == null) ? autoseed() : seed, 3), key);
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// Use the seed to initialize an ARC4 generator.
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var arc4 = new ARC4(key);
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// Mix the randomness into accumulated entropy.
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mixkey(tostring(arc4.S), pool);
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// Calling convention: what to return as a function of prng, seed, is_math.
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return (callback ||
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// If called as a method of Math (Math.seedrandom()), mutate Math.random
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// because that is how seedrandom.js has worked since v1.0. Otherwise,
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// it is a newer calling convention, so return the prng directly.
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function(prng, seed, is_math_call) {
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if (is_math_call) { math[rngname] = prng; return seed; }
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else return prng;
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})(
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// This function returns a random double in [0, 1) that contains
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// randomness in every bit of the mantissa of the IEEE 754 value.
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function() {
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var n = arc4.g(chunks), // Start with a numerator n < 2 ^ 48
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d = startdenom, // and denominator d = 2 ^ 48.
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x = 0; // and no 'extra last byte'.
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while (n < significance) { // Fill up all significant digits by
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n = (n + x) * width; // shifting numerator and
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d *= width; // denominator and generating a
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x = arc4.g(1); // new least-significant-byte.
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}
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while (n >= overflow) { // To avoid rounding up, before adding
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n /= 2; // last byte, shift everything
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d /= 2; // right using integer math until
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x >>>= 1; // we have exactly the desired bits.
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}
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return (n + x) / d; // Form the number within [0, 1).
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}, shortseed, this == math);
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};
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//
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// ARC4
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//
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// An ARC4 implementation. The constructor takes a key in the form of
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// an array of at most (width) integers that should be 0 <= x < (width).
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//
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// The g(count) method returns a pseudorandom integer that concatenates
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// the next (count) outputs from ARC4. Its return value is a number x
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// that is in the range 0 <= x < (width ^ count).
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//
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/** @constructor */
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function ARC4(key) {
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var t, keylen = key.length,
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me = this, i = 0, j = me.i = me.j = 0, s = me.S = [];
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// The empty key [] is treated as [0].
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if (!keylen) { key = [keylen++]; }
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// Set up S using the standard key scheduling algorithm.
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while (i < width) {
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s[i] = i++;
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}
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for (i = 0; i < width; i++) {
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s[i] = s[j = mask & (j + key[i % keylen] + (t = s[i]))];
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s[j] = t;
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}
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// The "g" method returns the next (count) outputs as one number.
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(me.g = function(count) {
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// Using instance members instead of closure state nearly doubles speed.
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var t, r = 0,
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i = me.i, j = me.j, s = me.S;
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while (count--) {
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t = s[i = mask & (i + 1)];
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r = r * width + s[mask & ((s[i] = s[j = mask & (j + t)]) + (s[j] = t))];
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}
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me.i = i; me.j = j;
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return r;
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// For robust unpredictability discard an initial batch of values.
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// See http://www.rsa.com/rsalabs/node.asp?id=2009
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})(width);
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}
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//
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// flatten()
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// Converts an object tree to nested arrays of strings.
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//
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function flatten(obj, depth) {
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var result = [], typ = (typeof obj), prop;
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if (depth && typ == 'object') {
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for (prop in obj) {
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try { result.push(flatten(obj[prop], depth - 1)); } catch (e) {}
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}
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}
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return (result.length ? result : typ == 'string' ? obj : obj + '\0');
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}
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//
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// mixkey()
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// Mixes a string seed into a key that is an array of integers, and
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// returns a shortened string seed that is equivalent to the result key.
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//
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function mixkey(seed, key) {
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var stringseed = seed + '', smear, j = 0;
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while (j < stringseed.length) {
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key[mask & j] =
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mask & ((smear ^= key[mask & j] * 19) + stringseed.charCodeAt(j++));
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}
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return tostring(key);
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}
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//
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// autoseed()
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// Returns an object for autoseeding, using window.crypto if available.
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//
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/** @param {Uint8Array|Navigator=} seed */
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function autoseed(seed) {
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try {
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global.crypto.getRandomValues(seed = new Uint8Array(width));
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return tostring(seed);
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} catch (e) {
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return [+new Date, global, (seed = global.navigator) && seed.plugins,
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global.screen, tostring(pool)];
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}
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}
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//
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// tostring()
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// Converts an array of charcodes to a string
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//
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function tostring(a) {
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return String.fromCharCode.apply(0, a);
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}
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//
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// When seedrandom.js is loaded, we immediately mix a few bits
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// from the built-in RNG into the entropy pool. Because we do
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// not want to intefere with determinstic PRNG state later,
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// seedrandom will not call math.random on its own again after
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// initialization.
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//
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mixkey(math[rngname](), pool);
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//
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// Nodejs and AMD support: export the implemenation as a module using
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// either convention.
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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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}
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// End anonymous scope, and pass initial values.
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})(
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this, // global window object
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[], // pool: entropy pool starts empty
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Math, // math: package containing random, pow, and seedrandom
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256, // width: each RC4 output is 0 <= x < 256
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6, // chunks: at least six RC4 outputs for each double
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52, // digits: there are 52 significant digits in a double
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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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'random'// rngname: name for Math.random and Math.seedrandom
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);
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