iOS NSDecimalNumber

• 加

var total: NSDecimalNumber = NSDecimalNumber.zero
let price1: NSDecimalNumber = 10
let price2: NSDecimalNumber = 5
total = price1.adding(price2)

• 减

var price: NSDecimalNumber = NSDecimalNumber.zero
let price1: NSDecimalNumber = 10
let price2: NSDecimalNumber = 5
price = price1.subtracting(price2)

• 乘

let price: NSDecimalNumber = 10
let count: NSDecimalNumber = 5
let total: NSDecimalNumber = price.multiplying(by: count)

• 除

let total: NSDecimalNumber = 20
let price: NSDecimalNumber = 5
let count: NSDecimalNumber = total.dividing(price)

• 四舍五入

/*
public enum RoundingMode : UInt {
        case plain // Round up on a tie

        case down // Always down == truncate

        case up // Always up

        case bankers // on a tie round so last digit is even
    }
*/
let round = NSDecimalNumberHandler(roundingMode: NSDecimalNumber.RoundingMode.bankers, scale: 2, raiseOnExactness: false, raiseOnOverflow: false, raiseOnUnderflow: false, raiseOnDivideByZero: true)
let orginPrice: NSDecimalNumber = 999.9999
let disCount: NSDecimalNumber = 0.75
let price = orginPrice.multiplying(by: disCount, withBehavior:round)

• 比较

let price1: NSDecimalNumber = 10
let price2: NSDecimalNumber = 5
let result: NSComparisonResult  = price1.compare(price2)
if result == NSOrderedAscending {
 } else if result == NSOrderedSame {
 } else if result == NSOrderedDescending {  
}

• 次方

let count: NSDecimalNumber = 5
let total: NSDecimalNumber = count.raising(toPower: 2)