# All files / seedrandom/lib xor4096.js

92.68% Statements 76/82
65.71% Branches 23/35
90% Functions 9/10
94.52% Lines 69/73

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     // A Javascript implementaion of Richard Brent's Xorgens xor4096 algorithm.
    //
    // This fast non-cryptographic random number generator is designed for
    // use in Monte-Carlo algorithms. It combines a long-period xorshift
    // generator with a Weyl generator, and it passes all common batteries
    // of stasticial tests for randomness while consuming only a few nanoseconds
    // for each prng generated.  For background on the generator, see Brent's
    // paper: "Some long-period random number generators using shifts and xors."
    // http://arxiv.org/pdf/1004.3115v1.pdf
    //
    // Usage:
    //
    // var xor4096 = require('xor4096');
    // random = xor4096(1);                        // Seed with int32 or string.
    // assert.equal(random(), 0.1520436450538547); // (0, 1) range, 53 bits.
    // assert.equal(random.int32(), 1806534897);   // signed int32, 32 bits.
    //
    // For nonzero numeric keys, this impelementation provides a sequence
    // identical to that by Brent's xorgens 3 implementaion in C.  This
    // implementation also provides for initalizing the generator with
    // string seeds, or for saving and restoring the state of the generator.
    //
    // On Chrome, this prng benchmarks about 2.1 times slower than
    // Javascript's built-in Math.random().

    (function(global, module, define) {

    function XorGen(seed) {
      var me = this;

      // Set up generator function.
      me.next = function() {
        var w = me.w,
            X = me.X, i = me.i, t, v;
        // Update Weyl generator.
        me.w = w = (w + 0x61c88647) | 0;
        // Update xor generator.
        v = X[(i + 34) & 127];
        t = X[i = ((i + 1) & 127)];
        v ^= v << 13;
        t ^= t << 17;
        v ^= v >>> 15;
        t ^= t >>> 12;
        // Update Xor generator array state.
        v = X[i] = v ^ t;
        me.i = i;
        // Result is the combination.
        return (v + (w ^ (w >>> 16))) | 0;
      };

      function init(me, seed) {
        var t, v, i, j, w, X = [], limit = 128;
        if (seed === (seed | 0)) {
          // Numeric seeds initialize v, which is used to generates X.
          v = seed;
          seed = null;
        } else {
          // String seeds are mixed into v and X one character at a time.
          seed = seed + '\0';
          v = 0;
          limit = Math.max(limit, seed.length);
        }
        // Initialize circular array and weyl value.
        for (i = 0, j = -32; j < limit; ++j) {
          // Put the unicode characters into the array, and shuffle them.
          if (seed) v ^= seed.charCodeAt((j + 32) % seed.length);
          // After 32 shuffles, take v as the starting w value.
          if (j === 0) w = v;
          v ^= v << 10;
          v ^= v >>> 15;
          v ^= v << 4;
          v ^= v >>> 13;
          if (j >= 0) {
            w = (w + 0x61c88647) | 0;     // Weyl.
            t = (X[j & 127] ^= (v + w));  // Combine xor and weyl to init array.
            i = (0 == t) ? i + 1 : 0;     // Count zeroes.
          }
        }
        // We have detected all zeroes; make the key nonzero.
        Iif (i >= 128) {
          X[(seed && seed.length || 0) & 127] = -1;
        }
        // Run the generator 512 times to further mix the state before using it.
        // Factoring this as a function slows the main generator, so it is just
        // unrolled here.  The weyl generator is not advanced while warming up.
        i = 127;
        for (j = 4 * 128; j > 0; --j) {
          v = X[(i + 34) & 127];
          t = X[i = ((i + 1) & 127)];
          v ^= v << 13;
          t ^= t << 17;
          v ^= v >>> 15;
          t ^= t >>> 12;
          X[i] = v ^ t;
        }
        // Storing state as object members is faster than using closure variables.
        me.w = w;
        me.X = X;
        me.i = i;
      }

      init(me, seed);
    }

    function copy(f, t) {
      t.i = f.i;
      t.w = f.w;
      t.X = f.X.slice();
      return t;
    };

    function impl(seed, opts) {
      Iif (seed == null) seed = +(new Date);
      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 (state.X) copy(state, xg);
        prng.state = function() { return copy(xg, {}); }
      }
      return prng;
    }

    Eif (module && module.exports) {
      module.exports = impl;
    } else if (define && define.amd) {
      define(function() { return impl; });
    } else {
      this.xor4096 = impl;
    }

    })(
      this,                                     // window object or global
      (typeof module) == 'object' && module,    // present in node.js
      (typeof define) == 'function' && define   // present with an AMD loader
    );