lighter/common/crypto/crc32.js

A lightweight Node.js framework

/**
 * Calculate a CRC32 hash for a string.
 *
 * @origin https://github.com/lighterio/lighter-common/common/crypto/crc32.js
 * @version 0.0.1
 */

module.exports = crc32

var cachedTable = buildTable()

function crc32 (str) {
  var l = str.length
  var codes = new Array(l)
  for (var i = 0, n = 0, c; i < l; ++i) {
    c = str.charCodeAt(i)
    if (c < 128) {
      codes[n++] = c
    } else if (c < 2048) {
      codes[n++] = (c >> 6) | 192
      codes[n++] = (c & 63) | 128
    } else {
      codes[n++] = (c >> 12) | 224
      codes[n++] = ((c >> 6) & 63) | 128
      codes[n++] = (c & 63) | 128
    }
  }
  var crc = -1
  var table = cachedTable
  l = codes.length
  for (i = 0; i < l; ++i) {
    c = (crc ^ codes[i]) & 255
    crc = (crc >>> 8) ^ table[c]
  }
  return (crc ^ -1) >>> 0
}

function buildTable () {
  var table = []
  for (var i = 0, j, crc; i < 256; ++i) {
    crc = i
    j = 8
    while (j--) {
      if ((crc & 1) === 1) {
        crc = (crc >>> 1) ^ 3988292384
      } else {
        crc >>>= 1
      }
    }
    table[i] = crc >>> 0
  }
  return table
}