Mongo's ObjectId generator

ObjectId.js

var MACHINE_ID = parseInt(Math.random() * 0xFFFFFF, 10);

ObjectID.prototype.generate = function(time) {
  if ('number' != typeof time) {
    time = ~~(Date.now()/1000);
  }

  // Use pid
  var pid = (typeof process === 'undefined' ? Math.floor(Math.random() * 100000) : process.pid) % 0xFFFF;
  var inc = this.get_inc();
  // Buffer used
  var buffer = new Buffer(12);
  // Encode time
  buffer[3] = time & 0xff;
  buffer[2] = (time >> 8) & 0xff;
  buffer[1] = (time >> 16) & 0xff;
  buffer[0] = (time >> 24) & 0xff;
  // Encode machine
  buffer[6] = MACHINE_ID & 0xff;
  buffer[5] = (MACHINE_ID >> 8) & 0xff;
  buffer[4] = (MACHINE_ID >> 16) & 0xff;
  // Encode pid
  buffer[8] = pid & 0xff;
  buffer[7] = (pid >> 8) & 0xff;
  // Encode index
  buffer[11] = inc & 0xff;
  buffer[10] = (inc >> 8) & 0xff;
  buffer[9] = (inc >> 16) & 0xff;
  // Return the buffer
  return buffer;
};