[SOLVED] Swift – Convert UInt8 byte to array of bits

Issue

I’m trying to decode a protobuff encoded message, so I need to convert the first byte (the key) in the protobuff message into bits, so I can find the field number. How do I convert a UInt8 (the byte) into an array of bits?

Pseudo Code

private func findFieldNum(from byte: UInt8) -> Int {
    //Byte is 0001 1010
    var fieldNumBits = byte[1] ++ byte[2] ++ byte[3] ++ byte[4] //concatentates bits to get 0011
    getFieldNum(from: fieldNumBits) //Converts 0011 to field number, 2^1 + 2^0 = 3
}

I saw this question, which converts an array of bits into array of bytes.

Solution

Here’s a basic function to get a Bit array from a byte:

func bits(fromByte byte: UInt8) -> [Bit] {
    var byte = byte
    var bits = [Bit](repeating: .zero, count: 8)
    for i in 0..<8 {
        let currentBit = byte & 0x01
        if currentBit != 0 {
            bits[i] = .one
        }

        byte >>= 1
    }

    return bits
}

Here, Bit is a custom enum type that I have defined as follows:

enum Bit: UInt8, CustomStringConvertible {
    case zero, one

    var description: String {
        switch self {
        case .one:
            return "1"
        case .zero:
            return "0"
        }
    }
}

With this setup, the output of the following code:

let byte: UInt8 = 0x1f

print(bits(fromByte: byte))

would be:

[1, 1, 1, 1, 1, 0, 0, 0]

Answered By – mohak

Answer Checked By – Dawn Plyler (BugsFixing Volunteer)