Decimal+Rounding.swift

/**
   Some numbers can have strange behaviour going back to Double or Float
   If rounding in Decimal it's best to keep it in Decimal until the point of display or transport in JSON

Read here: https://forums.swift.org/t/jsonencoder-encodable-floating-point-rounding-error/41390/6
**/

/*
  A helper that assists in rounding a Double to a given number of decimal places
  */
 public func rounded(_ value: Double, places: Int16) -> Decimal {
   let roundingBehavior = NSDecimalNumberHandler(
     roundingMode: .bankers,
     scale: places,
     raiseOnExactness: true,
     raiseOnOverflow: true,
     raiseOnUnderflow: true,
     raiseOnDivideByZero: true
   )

   return NSDecimalNumber(value: value).rounding(accordingToBehavior: roundingBehavior) as Decimal
 }

 /*
  A helper that assists in rounding a Float to a given number of decimal places
  */
 public func rounded(_ value: Float, places: Int16) -> Decimal {
   let roundingBehavior = NSDecimalNumberHandler(
     roundingMode: .bankers,
     scale: places,
     raiseOnExactness: true,
     raiseOnOverflow: true,
     raiseOnUnderflow: true,
     raiseOnDivideByZero: true
   )

   return NSDecimalNumber(value: value).rounding(accordingToBehavior: roundingBehavior) as Decimal
 }

/// examples

func testRoundedToDecimalPlaces_Double() {
     let amount: Double = 30.5657676754

     let roundedTo2dp = rounded(amount, places: 2)
     let roundedTo4dp = rounded(amount, places: 4)

     XCTAssertEqual(30.57, roundedTo2dp)
     XCTAssertEqual(30.5658, roundedTo4dp)
 }

func testRoundedToDecimalPlaces_Float() {
     let amount: Float = 30.5657676754

     let roundedTo2dp = rounded(amount, places: 2)
     let roundedTo4dp = rounded(amount, places: 4)

     XCTAssertEqual(30.57, roundedTo2dp)
     XCTAssertEqual(30.5658, roundedTo4dp)
 }