quick-hash/lib/index.js

Murmur hash optimized for performance, not collision avoidance.

'use strict'

/**
 * @id quickHash
 * @function quickHash
 * Murmur hash optimized for performance, not collision avoidance.
 * @param {string} key - the string to hash
 * @param {number} seed - a seed for hashing
 * @returns {string} hashOfKey - A string of 5 to 7 alpha-numeric characters
 */
module.exports = function (key, seed) {
  var remainder, bytes, h1, h1b, c1, c2, k1, i
  seed = 1
  remainder = key.length & 3 // key.length % 4
  bytes = key.length - remainder
  h1 = seed
  c1 = 0xcc9e2d51
  c2 = 0x1b873593
  i = 0

  while (i < bytes) {
    k1 =
      ((key.charCodeAt(i) & 0xff)) |
      ((key.charCodeAt(++i) & 0xff) << 8) |
      ((key.charCodeAt(++i) & 0xff) << 16) |
      ((key.charCodeAt(++i) & 0xff) << 24)
    ++i

    k1 = ((((k1 & 0xffff) * c1) + ((((k1 >>> 16) * c1) & 0xffff) << 16))) & 0xffffffff
    k1 = (k1 << 15) | (k1 >>> 17)
    k1 = ((((k1 & 0xffff) * c2) + ((((k1 >>> 16) * c2) & 0xffff) << 16))) & 0xffffffff

    h1 ^= k1
    h1 = (h1 << 13) | (h1 >>> 19)
    h1b = ((((h1 & 0xffff) * 5) + ((((h1 >>> 16) * 5) & 0xffff) << 16))) & 0xffffffff
    h1 = (((h1b & 0xffff) + 0x6b64) + ((((h1b >>> 16) + 0xe654) & 0xffff) << 16))
  }

  k1 = 0

  // @todo: replace with if else (faster)
  switch (remainder) {
    case 3: k1 ^= (key.charCodeAt(i + 2) & 0xff) << 16 //eslint-disable-line
    case 2: k1 ^= (key.charCodeAt(i + 1) & 0xff) << 8 //eslint-disable-line
    case 1: k1 ^= (key.charCodeAt(i) & 0xff) //eslint-disable-line
      k1 = (((k1 & 0xffff) * c1) + ((((k1 >>> 16) * c1) & 0xffff) << 16)) & 0xffffffff
      k1 = (k1 << 15) | (k1 >>> 17)
      k1 = (((k1 & 0xffff) * c2) + ((((k1 >>> 16) * c2) & 0xffff) << 16)) & 0xffffffff
      h1 ^= k1
  }

  h1 ^= key.length

  h1 ^= h1 >>> 16
  h1 = (((h1 & 0xffff) * 0x85ebca6b) + ((((h1 >>> 16) * 0x85ebca6b) & 0xffff) << 16)) & 0xffffffff
  h1 ^= h1 >>> 13
  h1 = ((((h1 & 0xffff) * 0xc2b2ae35) + ((((h1 >>> 16) * 0xc2b2ae35) & 0xffff) << 16))) & 0xffffffff
  h1 ^= h1 >>> 16

  return (h1 >>> 0).toString(36)
}