class CRC

# File lib/futurocube/crc.rb, line 2
def initialize
  @table = make_table(0x04C11DB7)
  reset
end

# File lib/futurocube/crc.rb, line 29
def crc
  @crc
end

# File lib/futurocube/crc.rb, line 7
def reset
  @crc = 0xFFFFFFFF
end

# File lib/futurocube/crc.rb, line 11
def update(input)
  crc = @crc
  table = @table

  # Original algorithm does it little-endian then iterates from the high byte.
  # I read it big-endian and then iterate from the low byte, saving some bit maths.
  input.unpack('N*').each do |data|
    4.times do
      table_index = (data & 0xFF) ^ (crc >> 24)
      crc = (crc << 8) & 0xFFFFFFFF
      crc = crc ^ table[table_index]
      data >>= 8
    end
  end

  @crc = crc
end

# File lib/futurocube/crc.rb, line 35
def make_table(poly)
  (0..255).map do |n|
    crc = n << 24
    8.times do
      if crc & 0x80000000 != 0
        crc = ((crc << 1) ^ poly) & 0xFFFFFFFF
      else
        crc <<= 1
      end
    end
    (crc & 0xFFFFFFFF)
  end
end