static int Main(string[] args)
{
if (args.Length < 1)
{
Console.WriteLine(PuzzleFileFns.StandardOneParamRequiredErrorMessage);
return(1);
}
var allLines = File.ReadAllLines(args[0]);
int payloadStartLine = PuzzleFileFns.GetLinePayloadStartsAt(allLines);
var payload = PuzzleFileFns.GetPayloadAsOneLongString(allLines, payloadStartLine);
Debug.Assert(payload.StartsWith(@"<~0/)?#c'P?"));
Debug.Assert(payload.EndsWith(@"ZOG^Hi`#W@:,!~>"));
Debug.Assert(payload.Contains("\n") == false);
Debug.Assert(BitwiseFns.FlipEverySecondBit(180) == 225);
Debug.Assert(BitwiseFns.RotateByteRight(225) == 240);
Func <byte, byte> bytePostProcess =
(inByte) => BitwiseFns.RotateByteRight(BitwiseFns.FlipEverySecondBit(inByte));
Debug.Assert(bytePostProcess(180) == 240);
var payloadSpan = Ascii85Fns.DecodeAsSpan(payload, 2);
var transformedBytes = payloadSpan.ToArray().Select(bytePostProcess).ToArray();
Console.Write(Encoding.ASCII.GetString(transformedBytes));
return(0);
}
/// <summary>
/// True if the byte has an even amount of bits and the parity bit (LSB) is zero,
/// Or the byte has an odd amount of bits and the parity bit is one.
/// </summary>
public static bool OneBitParityCheck(byte rawByte)
{
var parityBit = rawByte & 1;
var dataBits = (byte)(rawByte & 254); // clears lsb
var bitCount = BitwiseFns.GetBitCount(dataBits);
return(parityBit == 0 ? bitCount % 2 == 0 : bitCount % 2 == 1);
}