bwd_table = [
      0x00000000, 0xDB710641, 0x6D930AC3, 0xB6E20C82,
      0xDB261586, 0x005713C7, 0xB6B51F45, 0x6DC41904,
      0x6D3D2D4D, 0xB64C2B0C, 0x00AE278E, 0xDBDF21CF,
      0xB61B38CB, 0x6D6A3E8A, 0xDB883208, 0x00F93449,