swift

Swift Decimal 封装

用例

let num1 = "1.998"
let num2 = "2.258"
let num3 = "3.887"
let num4 = "4.32222"

let allNum = num1.add(num: num2).reduction(num: num3).division(num: num4).numType(num: 4, type: String.RoundingType.down)
DDLogDebug("\n\(allNum)\n")

let addNum = num1.add(num: num2)
DDLogDebug("\n\(addNum)\n")

let minusNum = num2.reduction(num: num1)
DDLogDebug("\n\(minusNum)\n")

let multiplying = num3.division(num: num4)
DDLogDebug("\n\(multiplying)\n")

let divNum = num4.take(num: num1)
DDLogDebug("\n\(divNum)\n")

/***********    DecimalExtension        *******/
extension String {
  enum RoundingType : UInt {
    case plain   //Round up on a tie
    case down    //Always down == truncate
    case giveUp  //Always up
    case bankers //on a tie round so last digit is even
  }

  // MARK: - + string addition
  // - Parameter numberString: string
  // - Returns: result string
  func add(numberString:String) -> String {
    let number1 = NSDecimalNumber(string: self)
    let number2 = NSDecimalNumber(string: numberString)
    let summation = number1.adding(number2)
    return summation.stringValue
  }

  // MARK: -  - string subtraction
  // - Parameter numberString: string
  // - Returns: result string
  func reduction(numberString:String) -> String {
    let number1 = NSDecimalNumber(string: self)
    let number2 = NSDecimalNumber(string: numberString)
    let summation = number1.subtracting(number2)
    return summation.stringValue
  }

  // MARK: - * string multiplication
  // - Parameter numberString: string
  // - Returns: result string
  func take(numberString:String) -> String {
    let number1 = NSDecimalNumber(string: self)
    let number2 = NSDecimalNumber(string: numberString)
    let summation = number1.multiplying(by: number2)
    return summation.stringValue
  }

  // MARK: - / string division
  // - Parameter numberString: string
  // - Returns: result string
  func division(numberString:String) -> String {
    let number1 = NSDecimalNumber(string: self)
    let number2 = NSDecimalNumber(string: numberString)
    let summation = number1.dividing(by:number2)
    return summation.stringValue
  }

  // MARK: - keep a few decimal places and choose the type
  // - Parameter num: keep a few decimal places  type : choose the type
  // - Returns: string
  func numType(num : Int , type : RoundingType) -> String {
    /*
    enum NSRoundingMode : UInt {

    case RoundPlain     // Round up on a tie
    case RoundDown      // Always down == truncate
    case RoundUp        // Always up
    case RoundBankers   // on a tie round so last digit is even
  }
    */

    // 90.7049 + 0.22
    var rounding = NSDecimalNumber.RoundingMode.down
    switch type {
      case RoundingType.plain:
      rounding = NSDecimalNumber.RoundingMode.plain
      case RoundingType.down:
      rounding = NSDecimalNumber.RoundingMode.down
      case RoundingType.giveUp:
      rounding = NSDecimalNumber.RoundingMode.up
      case RoundingType.bankers:
      rounding = NSDecimalNumber.RoundingMode.bankers
    }
    let roundUp = NSDecimalNumberHandler(roundingMode: rounding, scale:Int16(num), raiseOnExactness: false, raiseOnOverflow: false, raiseOnUnderflow: false, raiseOnDivideByZero: true)

    let discount = NSDecimalNumber(string: self)
    let subtotal = NSDecimalNumber(string: "0")

    let total = subtotal.adding(discount, withBehavior: roundUp).stringValue

    var mutstr = String()

    if total.contains(".") {
      let float = total.components(separatedBy: ".").last!
      if float.count == Int(num) {
        mutstr .append(total)
        return mutstr
      } else {
        mutstr.append(total)
        let all = num - float.count
        for _ in 1...all {
          mutstr += "0"
        }
        return mutstr
      }
    } else {
      mutstr.append(total)
      if num == 0 {
      } else {
        for _ in 1...num {
          mutstr += "0"
        }
      }
      return mutstr
    }
  }
}

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