Wiegand & OSDP Physical Access Control Protocols

public class WiegandDecoder
{
    public static bool TryDecodeWiegand26(uint raw26Bits, out ushort facilityCode, out ushort cardNumber)
    {
        facilityCode = 0;
        cardNumber = 0;

        // Bit 25: Even Parity over bits 1-12
        // Bits 24..17: Facility Code (8 bits)
        // Bits 16..1: Card Number (16 bits)
        // Bit 0: Odd Parity over bits 13-24

        uint evenParityBit = (raw26Bits >> 25) & 1;
        uint facility = (raw26Bits >> 17) & 0xFF;
        uint card = (raw26Bits >> 1) & 0xFFFF;
        uint oddParityBit = raw26Bits & 1;

        // Calculate Even Parity on upper 12 bits
        uint upper12 = (raw26Bits >> 13) & 0xFFF;
        uint calcEven = (uint)(CountSetBits(upper12) % 2);

        // Calculate Odd Parity on lower 12 bits
        uint lower12 = (raw26Bits >> 1) & 0xFFF;
        uint calcOdd = (uint)((CountSetBits(lower12) % 2 == 0) ? 1 : 0);

        if (evenParityBit != calcEven || oddParityBit != calcOdd)
            return false; // Parity check failed

        facilityCode = (ushort)facility;
        cardNumber = (ushort)card;
        return true;
    }

    private static int CountSetBits(uint n)
    {
        int count = 0;
        while (n > 0) { count += (int)(n & 1); n >>= 1; }
        return count;
    }
}