String CRC in CoffeeScript

crc.coffee

# tested against OS X cksum: `echo -n 'hello' | cksum -o 3` == "hello".crc32()

String.CRC32Table =  # ref: http://www.w3.org/TR/PNG/#D-CRCAppendix
  for c in [0..255]  # (can clobber c with impunity below thanks to CoffeeScript)
    for k in [0..7]
      c = if c & 1 then 0xedb88320 ^ (c >>> 1) else (c >>> 1)
    c >>> 0

String::crc32 = (crc = 0xffffffff) ->
  for i in [0...@length] by 1
    crc = String.CRC32Table[(crc ^ @charCodeAt i) & 0xff] ^ (crc >>> 8)
  (crc ^ 0xffffffff) >>> 0