public static class IntergalacticTransmission { private const byte InitUpperMask = (byte)0xFE; public static byte[] GetTransmitSequence(byte[] message) { List transmitSeq = new List(); byte carry = 0; byte upperMask = InitUpperMask; for (int i = 0; i < message.Length; i++) { if (upperMask == 0) { // The carry now contains 7 bits. Flush the carry out. transmitSeq.Add(AddParity(carry)); carry = 0; upperMask = 0xFE; } int shiftPlaces = byte.TrailingZeroCount(upperMask); int current = (carry << (8 - shiftPlaces)) | (message[i] >>> shiftPlaces); transmitSeq.Add(AddParity((byte)current)); // Update parameters for next round. carry = (byte)(message[i] & (~upperMask)); // Shorten the upper mask. upperMask = (byte)(upperMask << 1); } if (upperMask != InitUpperMask) { byte lastGroup = (byte)(carry << byte.PopCount(upperMask)); // We have left over carry data transmitSeq.Add(AddParity(lastGroup)); } return transmitSeq.ToArray(); } private static byte AddParity(byte source) { if (byte.PopCount((byte)(source & 0x7F)) % 2 == 0) { return (byte)(source << 1); } return (byte)((source << 1) | 1); } public static byte[] DecodeSequence(byte[] receivedSeq) { if (receivedSeq.Length == 0) { return []; } List decodedMessage = new List(); byte byteToAdd = 0x00; byte upperMask = 0xFF; for (int i = 0; i < receivedSeq.Length; i++) { if (upperMask == 0xFF) { // We've completed a complete round. // Current byte too short. byteToAdd = GetByteData(receivedSeq[i]); upperMask = 0x80; continue; } byte currentByteData = GetByteData(receivedSeq[i]); byte contribution = (byte)(currentByteData >>> byte.TrailingZeroCount(upperMask)); decodedMessage.Add((byte)(byteToAdd | contribution)); // Update parameters for next round byteToAdd = (byte)((currentByteData & ~(upperMask | 0x01)) << byte.PopCount(upperMask)); upperMask = (byte)((upperMask >> 1) | 0x80); } return decodedMessage.ToArray(); } private static byte GetByteData(byte data) { if (byte.PopCount(data) % 2 != 0) { throw new ArgumentException("Byte has incorrect parity"); } return (byte)(data & 0xFE); } }