Convert UInt to UInt8(byte) Array in swift.

UInt_extension.swift

protocol UIntToBytesConvertable {
    var toBytes: [UInt8] { get }
}

extension UIntToBytesConvertable {
    func toByteArr<T: BinaryInteger>(endian: T, count: Int) -> [UInt8] {
        var _endian = endian
        let bytePtr = withUnsafePointer(to: &_endian) {
            $0.withMemoryRebound(to: UInt8.self, capacity: count) {
                UnsafeBufferPointer(start: $0, count: count)
            }
        }
        return [UInt8](bytePtr)
    }
}

extension UInt16: UIntToBytesConvertable {
    var toBytes: [UInt8] {
        if CFByteOrderGetCurrent() == Int(CFByteOrderLittleEndian.rawValue) {
            return toByteArr(endian: self.littleEndian,
                         count: MemoryLayout<UInt16>.size)
        } else {
            return toByteArr(endian: self.bigEndian,
                             count: MemoryLayout<UInt16>.size)
        }
    }
}

extension UInt32: UIntToBytesConvertable {
    var toBytes: [UInt8] {
        if CFByteOrderGetCurrent() == Int(CFByteOrderLittleEndian.rawValue) {
        return toByteArr(endian: self.littleEndian,
                         count: MemoryLayout<UInt32>.size)
        } else {
            return toByteArr(endian: self.bigEndian,
                             count: MemoryLayout<UInt32>.size)
        }
    }
}

extension UInt64: UIntToBytesConvertable {
    var toBytes: [UInt8] {
        if CFByteOrderGetCurrent() == Int(CFByteOrderLittleEndian.rawValue) {
        return toByteArr(endian: self.littleEndian,
                         count: MemoryLayout<UInt64>.size)
        } else {
            return toByteArr(endian: self.bigEndian,
                             count: MemoryLayout<UInt64>.size)
        }
    }
}

Another way to convert UInt to UInt8 is to shift bits. It normally works faster that unsafe pointer

extension UInt16 {
    /// Convert a UInt16 to an array of UInt8.
    /// - Returns: An array of UInt8 representing the UInt16 value.
    var toUInt8: [UInt8] {
        return [
            UInt8(self >> 8),
            UInt8(self & 0xff)
        ]
    }
}

extension UInt32 {
    /// Convert a UInt32 to an array of UInt8.
    /// - Returns: An array of UInt8 representing the UInt32 value.
    var toUInt8: [UInt8] {
        return [
            UInt8((self >> 24) & 0xff),
            UInt8((self >> 16) & 0xff),
            UInt8((self >> 8) & 0xff),
            UInt8(self & 0xff)
        ]
    }
}