Another BCD byte[] to int and back again

Question

Im having trouble with some conversions, and can´t find whats wrong with the code, or with the idea of what it has to do.

I have the following byte[]

byte[] bytes = {0xFF, 0xFF, 0xFE};

which I convert into ulong this way:

ulong next = ((uint)((((0x00 << 4) | bytes[0]) << 16) | ((bytes[1] << 8) | bytes[2])));

next thing I add 1 to next:

next++;

Then, I want to convert the ulong, back to the byte array. I tryed with several bcd algorithms found here and on the web, but I cannot get the result I am expecting:

byte[] bytes = {0xFF, 0xFF, 0xFF};

insted of

{ 0x15, 0x72, 0x77, 0x16}

which I am getting with most of the solutions I have tryed.

Here is one of the algorithms I have used:

static Byte[] CopyAsBCD(UInt32 value)
        {
            Byte[] buffer = new byte[4];
            Int32 offset = 0;
            var length = 4;
            var s = value.ToString();
            var stringIndex = s.Length - 1;
            var bufferIndex = offset + length - 1;
            var isLower = true;

            try
            {
                while (bufferIndex >= offset && stringIndex > -1)
                {

                    if (isLower)
                        buffer[bufferIndex] = Byte.Parse(s[stringIndex].ToString());
                    else
                        buffer[bufferIndex] += (Byte)(Byte.Parse(s[stringIndex].ToString()) << 4);

                    if (!isLower)
                        bufferIndex--;
                    isLower = !isLower;
                    stringIndex--;
                }

            }
            catch
            {
            }
            return buffer;
        }

What I am doing wrong? or I have a concept problem?

Answer 1

Can you not just use:

//Array padded to 8 bytes, to represent a ulong
byte[] bytes = {0, 0, 0, 0, 0, 0xFF, 0xFF, 0xFE};

var longBytes = BitConverter.ToUInt64(bytes, 0);

var arrayBytes = BitConverter.GetBytes(longBytes);

Note: you may need to reverse the array, depending on the Endianness of the system you're on (in which case you may need to add padding to the other side).