--- /dev/null
+// seedrandom.js
+// Author: David Bau 3/11/2010
+//
+// Defines a method Math.seedrandom() that, when called, substitutes
+// an explicitly seeded RC4-based algorithm for Math.random(). Also
+// supports automatic seeding from local or network sources of entropy.
+//
+// Usage:
+//
+// <script src=http://davidbau.com/encode/seedrandom-min.js></script>
+//
+// Math.seedrandom('yipee'); Sets Math.random to a function that is
+// initialized using the given explicit seed.
+//
+// Math.seedrandom(); Sets Math.random to a function that is
+// seeded using the current time, dom state,
+// and other accumulated local entropy.
+// The generated seed string is returned.
+//
+// Math.seedrandom('yowza', true);
+// Seeds using the given explicit seed mixed
+// together with accumulated entropy.
+//
+// <script src="http://bit.ly/srandom-512"></script>
+// Seeds using physical random bits downloaded
+// from random.org.
+//
+// Examples:
+//
+// Math.seedrandom("hello"); // Use "hello" as the seed.
+// document.write(Math.random()); // Always 0.5463663768140734
+// document.write(Math.random()); // Always 0.43973793770592234
+// var rng1 = Math.random; // Remember the current prng.
+//
+// var autoseed = Math.seedrandom(); // New prng with an automatic seed.
+// document.write(Math.random()); // Pretty much unpredictable.
+//
+// Math.random = rng1; // Continue "hello" prng sequence.
+// document.write(Math.random()); // Always 0.554769432473455
+//
+// Math.seedrandom(autoseed); // Restart at the previous seed.
+// document.write(Math.random()); // Repeat the 'unpredictable' value.
+//
+// Notes:
+//
+// Each time seedrandom('arg') is called, entropy from the passed seed
+// is accumulated in a pool to help generate future seeds for the
+// zero-argument form of Math.seedrandom, so entropy can be injected over
+// time by calling seedrandom with explicit data repeatedly.
+//
+// On speed - This javascript implementation of Math.random() is about
+// 3-10x slower than the built-in Math.random() because it is not native
+// code, but this is typically fast enough anyway. Seeding is more expensive,
+// especially if you use auto-seeding. Some details (timings on Chrome 4):
+//
+// Our Math.random() - avg less than 0.002 milliseconds per call
+// seedrandom('explicit') - avg less than 0.5 milliseconds per call
+// seedrandom('explicit', true) - avg less than 2 milliseconds per call
+// seedrandom() - avg about 38 milliseconds per call
+//
+// LICENSE (BSD):
+//
+// Copyright 2010 David Bau, all rights reserved.
+//
+// Redistribution and use in source and binary forms, with or without
+// modification, are permitted provided that the following conditions are met:
+//
+// 1. Redistributions of source code must retain the above copyright
+// notice, this list of conditions and the following disclaimer.
+//
+// 2. Redistributions in binary form must reproduce the above copyright
+// notice, this list of conditions and the following disclaimer in the
+// documentation and/or other materials provided with the distribution.
+//
+// 3. Neither the name of this module nor the names of its contributors may
+// be used to endorse or promote products derived from this software
+// without specific prior written permission.
+//
+// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+// "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+// LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+// A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+// OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+// SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+// LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+// DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+// THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+// (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+// OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+//
+/**
+ * All code is in an anonymous closure to keep the global namespace clean.
+ *
+ * @param {number=} overflow
+ * @param {number=} startdenom
+ */
+(function (pool, math, width, chunks, significance, overflow, startdenom) {
+
+
+//
+// seedrandom()
+// This is the seedrandom function described above.
+//
+math['seedrandom'] = function seedrandom(seed, use_entropy) {
+ var key = [];
+ var arc4;
+
+ // Flatten the seed string or build one from local entropy if needed.
+ seed = mixkey(flatten(
+ use_entropy ? [seed, pool] :
+ arguments.length ? seed :
+ [new Date().getTime(), pool, window], 3), key);
+
+ // Use the seed to initialize an ARC4 generator.
+ arc4 = new ARC4(key);
+
+ // Mix the randomness into accumulated entropy.
+ mixkey(arc4.S, pool);
+
+ // Override Math.random
+
+ // This function returns a random double in [0, 1) that contains
+ // randomness in every bit of the mantissa of the IEEE 754 value.
+
+ math['random'] = function random() { // Closure to return a random double:
+ var n = arc4.g(chunks); // Start with a numerator n < 2 ^ 48
+ var d = startdenom; // and denominator d = 2 ^ 48.
+ var x = 0; // and no 'extra last byte'.
+ while (n < significance) { // Fill up all significant digits by
+ n = (n + x) * width; // shifting numerator and
+ d *= width; // denominator and generating a
+ x = arc4.g(1); // new least-significant-byte.
+ }
+ while (n >= overflow) { // To avoid rounding up, before adding
+ n /= 2; // last byte, shift everything
+ d /= 2; // right using integer math until
+ x >>>= 1; // we have exactly the desired bits.
+ }
+ return (n + x) / d; // Form the number within [0, 1).
+ };
+
+ // Return the seed that was used
+ return seed;
+};
+
+//
+// ARC4
+//
+// An ARC4 implementation. The constructor takes a key in the form of
+// an array of at most (width) integers that should be 0 <= x < (width).
+//
+// The g(count) method returns a pseudorandom integer that concatenates
+// the next (count) outputs from ARC4. Its return value is a number x
+// that is in the range 0 <= x < (width ^ count).
+//
+/** @constructor */
+function ARC4(key) {
+ var t, u, me = this, keylen = key.length;
+ var i = 0, j = me.i = me.j = me.m = 0;
+ me.S = [];
+ me.c = [];
+
+ // The empty key [] is treated as [0].
+ if (!keylen) { key = [keylen++]; }
+
+ // Set up S using the standard key scheduling algorithm.
+ while (i < width) { me.S[i] = i++; }
+ for (i = 0; i < width; i++) {
+ t = me.S[i];
+ j = lowbits(j + t + key[i % keylen]);
+ u = me.S[j];
+ me.S[i] = u;
+ me.S[j] = t;
+ }
+
+ // The "g" method returns the next (count) outputs as one number.
+ me.g = function getnext(count) {
+ var s = me.S;
+ var i = lowbits(me.i + 1); var t = s[i];
+ var j = lowbits(me.j + t); var u = s[j];
+ s[i] = u;
+ s[j] = t;
+ var r = s[lowbits(t + u)];
+ while (--count) {
+ i = lowbits(i + 1); t = s[i];
+ j = lowbits(j + t); u = s[j];
+ s[i] = u;
+ s[j] = t;
+ r = r * width + s[lowbits(t + u)];
+ }
+ me.i = i;
+ me.j = j;
+ return r;
+ };
+ // For robust unpredictability discard an initial batch of values.
+ // See http://www.rsa.com/rsalabs/node.asp?id=2009
+ me.g(width);
+}
+
+//
+// flatten()
+// Converts an object tree to nested arrays of strings.
+//
+/** @param {Object=} result
+ * @param {string=} prop */
+function flatten(obj, depth, result, prop) {
+ result = [];
+ if (depth && typeof(obj) == 'object') {
+ for (prop in obj) {
+ if (prop.indexOf('S') < 5) { // Avoid FF3 bug (local/sessionStorage)
+ try { result.push(flatten(obj[prop], depth - 1)); } catch (e) {}
+ }
+ }
+ }
+ return result.length ? result : '' + obj;
+}
+
+//
+// mixkey()
+// Mixes a string seed into a key that is an array of integers, and
+// returns a shortened string seed that is equivalent to the result key.
+//
+/** @param {number=} smear
+ * @param {number=} j */
+function mixkey(seed, key, smear, j) {
+ seed += ''; // Ensure the seed is a string
+ smear = 0;
+ for (j = 0; j < seed.length; j++) {
+ key[lowbits(j)] =
+ lowbits((smear ^= key[lowbits(j)] * 19) + seed.charCodeAt(j));
+ }
+ seed = '';
+ for (j in key) { seed += String.fromCharCode(key[j]); }
+ return seed;
+}
+
+//
+// lowbits()
+// A quick "n mod width" for width a power of 2.
+//
+function lowbits(n) { return n & (width - 1); }
+
+//
+// The following constants are related to IEEE 754 limits.
+//
+startdenom = math.pow(width, chunks);
+significance = math.pow(2, significance);
+overflow = significance * 2;
+
+//
+// When seedrandom.js is loaded, we immediately mix a few bits
+// from the built-in RNG into the entropy pool. Because we do
+// not want to intefere with determinstic PRNG state later,
+// seedrandom will not call math.random on its own again after
+// initialization.
+//
+mixkey(math.random(), pool);
+
+// End anonymous scope, and pass initial values.
+})(
+ [], // pool: entropy pool starts empty
+ Math, // math: package containing random, pow, and seedrandom
+ 256, // width: each RC4 output is 0 <= x < 256
+ 6, // chunks: at least six RC4 outputs for each double
+ 52 // significance: there are 52 significant digits in a double
+);
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