C# - how to put 4 bit and 12 bit into 2 bytes

Question

I have 2 bytes that should populate this way:

first number (4b) second number (12b)

So 4 bit can be between 1-15 And 12 bit can be between 1-50

So i have this Bytes Array:

byte[] packetArrayBytes = new byte[Length];

Answer 1

The way I've understood the question is that you've got these two (presumably) unsigned integers a and b: (I'll be writing them in hexadecimal to make it easier to read)

a: 0x0000000X

b: 0x00000XXX

Where a is the 4-bit number and b is the 12-bit one, with the Xs marking the bits containing the relevant values.

You want to store them in two separate 8-bit chunks: c: 0x00 and d: 0x00

So you need to shift the bits into position, like this:

byte[] packetArrayBytes = new byte[2];

uint intA = 0xF;   // Allowed range is 0-15   (0x0-0xF)
uint intB = 0xABC; // Allowed range is 0-4095 (0x0-0xFFF)

// Need to convert from uint to bytes:
byte[] bytesA = BitConverter.GetBytes(intA);
byte[] bytesB = BitConverter.GetBytes(intB);
byte a = bytesA[0]; // a is 0x0F
byte b = bytesB[1]; // b is 0x0A
int c = 0x00;      // c is 0x00
int d = bytesB[0]; // d is 0xBC

// Mask out 4 least significant bits of a,
// then shift 4 bits left to place them in the most significant bits (of the byte),
// then OR them into c.
c |= (a & 0x0F) << 4;  // c is now 0xF0

// Mask out 4 least significant bits of b,
// then OR them into c.
c |= b & 0x0F;   // c is now 0xFA

packetArrayBytes[0] = (Byte)c;
packetArrayBytes[1] = (Byte)d;

Console.WriteLine(BitConverter.ToString(packetArrayBytes)); // Prints "FA-BC"

After doing these operations, the values of a and b should be placed in the bytes c and d like this: c: 0xFA d: 0xBC. Which you can then place into your array.

To get the values back you just do these same operations in reverse.

If a and b are signed values, I believe the same operations work, but you'll have to make sure you're not interpreting them as unsigned when reading the data back into numbers.