fast-uuid.js

'use strict';

var crypto = require('crypto');
var pool = 31 * 128; // 36 chars minus 4 dashes and 1 four
var r = crypto.randomBytes(pool);
var j = 0;
var str = "10000000-1000-4000-8000-100000000000";
var len = str.length; // 36
var strs = [];

strs.length = len;
strs[8] = '-';
strs[13] = '-';
strs[18] = '-';
strs[23] = '-';

function uuid(){
  var ch;
  var chi;

  for (chi = 0; chi < len; chi++) {
    ch = str[chi];
    if ('-' === ch || '4' === ch) {
      strs[chi] = ch;
      continue;

    }

    // no idea why, but this is almost 4x slow if either
    // the increment is moved below or the >= is changed to >
    j++;
    if (j >= r.length) {
      r = crypto.randomBytes(pool);
      j = 0;

    }

    if ('8' === ch) {
      strs[chi] = (8 + r[j] % 4).toString(16);
      continue;

    }

    strs[chi] = (r[j] % 16).toString(16);

  }

  return strs.join('');

}

module.exports = { v4: uuid };