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)
        }
    }
}

Hi, Very cool! How do I do the inverse in SWIFT?

I have a ton of files with binary data of 16 bit unsigned integer values, that I can already convert into a [UInt8] array. Because these files can be very large, I would need an efficient way to convert either the data directly or the UInt8 array into a [UInt16] array. I am not sure if the data are little or big endian. Thank you for your help.

Hi, @Planet30 .

1. If you run the codes in the same machine, you don't need to worry about endian. You can get the endian information from "CFByteOrderGetCurrent()".

2. I think you can make a function by combination of CFByteOrderGetCurrent and bit shift operator.

Thank you @kimji81 for your quick answer concerning the endianness!

How do I convert the data from [UInt8] to [UInt16]? The inverse of what you showed above.

Or is there a way to directly load the binary data into the [UInt16] array?

@Planet30

As the image above, we don't need to order of the bytes and just use the bit shift operator.
ex)
let arrayOfBytes = [0x12,0x34]
var uintOf16 = arrayOfBytes[0] << 8 | arrayOfBytes[1]