tetris-prng/perf.js

A Fibonacci linear feedback shift register used as a PRNG (Pseudo-random Number Generator), as in NES Tetris.

function readable() {
  var value = 0x8988 >>> 0;
  return function () {
    var bit0 = (value >> 16) & 1;
    var bit1 = (value >> 15) & 1;
    var bit2 = (value >> 13) & 1;
    var bit3 = (value >> 4) & 1;
    var leftmostBit = bit0 ^ bit1 ^ bit2 ^ bit3;
    return (value = ((leftmostBit << 31) | (value >>> 1)) >>> 0);
  }
}

function inlined() {
  var value = 0x8988 >>> 0;
  return function () {
    return (value = (((((value >> 16) & 1) ^ ((value >> 15) & 1) ^ ((value >> 13) & 1) ^ ((value >> 4) & 1)) << 31) | (value >>> 1)) >>> 0);
  }
}

var assert = require('assert');
var r = readable();
var i = inlined();
assert(r() === i());
assert(r() === i());
assert(r() === i());