mersenne-twister.js

/*
  Implemented pseudocode available at 
  
  http://en.wikipedia.org/wiki/Mersenne_twister
  
  as an asm.js module to learn about asm.js
*/
function MersenneTwister(stdlib, foreign, heap) {
  "use asm";

  //imports
  var imul = stdlib.Math.imul;
  
  //constants
  var LW = 0xffff;
  var HW = 0xffff0000;
  var length = 624;
  var offset = 397;
  
  //internal state
  var mt = new stdlib.Uint32Array(heap);
  var temp = 0;
  var temp2 = 0;
  var i = 0;
  
  //exposed functions
  function init(seed) {
    seed = seed|0;
    
    mt[0] = seed >>> 0;
    for (i = 1; (i>>>0) < (length>>>0); i = (i + 1)|0) {
      temp = mt[((i-1)<<2)>>2]|0;
      temp = temp ^ (temp >>> 30);
      temp2 = (temp & HW) >>> 16;
      temp2 = imul(temp2, 1812433253)|0;
      temp2 = temp2 & LW; //truncate bits higher than 0xffff
      temp2 = temp2 << 16;
      temp = imul((temp & LW), 1812433253)|0;
      mt[(i<<2)>>2] = (temp + temp2 + i) >>> 0;
    }
    i = 0;
  }
  
  function rand() {
    if (i>>>0 == 0) { 
      for (i = 1; (i>>>0) < (length>>>0); i = (i + 1)|0) {
        temp = ((mt[(i<<2)>>2] & 0x80000000) + (mt[((((i+1)>>>0) % (length>>>0))<<2)>>2] & 0x7fffffff))|0;
        temp2 = (temp + (mt[((((i+offset)>>>0) % (length>>>0))<<2)>>2]|0))|0;
        if ((temp & 1) == 1) {
          temp2 = temp2 ^ 2567483615;
        }
        mt[(i<<2)>>2] = temp2;
      }
      i = 0;
    }
    
    temp = mt[(i<<2)>>2]|0;
    i = (((i + 1)>>>0) % (length>>>0))|0;
 
    /* Tempering */
    temp = (temp>>>0) ^ (temp >>> 11);
    temp = (temp>>>0) ^ (temp << 7) & 0x9d2c5680;
    temp = (temp>>>0) ^ (temp << 15) & 0xefc60000;
    temp = (temp>>>0) ^ (temp >>> 18);
 
    return (temp >>> 0)|0;
  }
  
  return { init: init, rand: rand };
};