UnicodeScalar+hexNibble.swift

/** Extensions to UnicodeScalar
 */
extension UnicodeScalar {
  /** Unicode scalar errors
   */
  enum UnicodeScalarError: String, Error {
    case illegalHexValue
  }

  /** Get the byte value of a hex nibble
   */
  func hexNibble() throws -> Byte {
    switch self {
    case UnicodeScalar(unicodeScalarLiteral:"0")...UnicodeScalar(unicodeScalarLiteral:"9"):
      return Byte(self.value - UnicodeScalar(unicodeScalarLiteral:"0").value)
      
    case UnicodeScalar(unicodeScalarLiteral:"a")...UnicodeScalar(unicodeScalarLiteral:"f"):
      return Byte(self.value - UnicodeScalar(unicodeScalarLiteral:"a").value + 0xa)
      
    case UnicodeScalar(unicodeScalarLiteral:"A")...UnicodeScalar(unicodeScalarLiteral:"F"):
      return Byte(self.value - UnicodeScalar(unicodeScalarLiteral:"A").value + 0xa)
      
    default:
      throw UnicodeScalarError.illegalHexValue
    }
  }
}