code: function unpack (bits, offset, length) {
      var mask = 0xffffffff, shift
      mask = mask >>> (32 - bits)
      mask = mask >>> (bits - length)
      shift = bits - offset - length
      shift = shift ? 'value >>> ' + shift : 'value'
      return shift + ' & 0x' + mask.toString(16)
  }
docs: TODO Module tidy; find a better name, better place to live.