Data extension method hexEncodedString

gistfile1.txt

extension Data {
    struct HexEncodingOptions: OptionSet {
        let rawValue: Int
        static let uppercase = HexEncodingOptions(rawValue: 0)
        static let lowercase = HexEncodingOptions(rawValue: 1 << 0)
    }
    func hexEncodedString(options: HexEncodingOptions = []) -> String {
        let hexDigits = Array((options.contains(.lowercase) ? "0123456789abcdef" : "0123456789ABCDEF").utf16)
        var dump: [unichar] = []
        var ascii: [unichar] = []
        dump.reserveCapacity(2 * count + (count + 7)/8 + 70 + ((count + 63)/64) * 35) // div by 8,64 rounding up, 35="| "+ascii+nl, 70=for worstcase 1 byte on last row
        ascii.reserveCapacity(32)
        var digitCount = 0
        for byte in self {
            dump.append(hexDigits[Int(byte / 16)])
            dump.append(hexDigits[Int(byte % 16)])
            ascii.append((isprint(Int32(byte)) != 0) ? unichar(byte) : 46) // "."
            
            digitCount += 2
            if digitCount % 8 == 0 {
                dump.append(32)
            }
            if digitCount % 64 == 0 {
                dump.append(124) // "|"
                dump.append(32)
                dump.append(contentsOf: ascii)
                dump.append(10) // nl
                ascii = []
                digitCount = 0
            }
        }
        if digitCount != 0 {
            let digits = 64 - digitCount
            let separators = (digits + 7) / 8 // div by 8 rounding up
            dump.append(contentsOf: Array<unichar>(repeating: 32, count: digits + separators))
            dump.append(124) // "|"
            dump.append(32)
            dump.append(contentsOf: ascii)
            dump.append(10) // nl
        }
        return String(utf16CodeUnits: dump, count: dump.count)
    }
}