NSDecimalNumber簡(jiǎn)介
蘋(píng)果針對(duì)浮點(diǎn)類型計(jì)算精度問(wèn)題提供出來(lái)的計(jì)算類投储，基于十進(jìn)制的科學(xué)計(jì)數(shù)法來(lái)計(jì)算玛歌，同時(shí)可以指定舍入模式昙读，一般用于貨幣計(jì)算。中國(guó)貨幣最小流通單位是分竭讳，也就是小數(shù)點(diǎn)后兩位创葡。
NSDecimalNumberHandler

/**
 初始化方法
 @param roundingMode 舍入方式
 @param scale 小數(shù)點(diǎn)后舍入值的位數(shù)
 @param exact 精度錯(cuò)誤處理
 @param overflow 溢出錯(cuò)誤處理
 @param underflow 下溢錯(cuò)誤處理
 @param divideByZero 除以0的錯(cuò)誤處理
 @return NSDecimalNumberHandler對(duì)象
 */
+ (instancetype)decimalNumberHandlerWithRoundingMode:(NSRoundingMode)roundingMode scale:(short)scale raiseOnExactness:(BOOL)exact raiseOnOverflow:(BOOL)overflow raiseOnUnderflow:(BOOL)underflow raiseOnDivideByZero:(BOOL)divideByZero;

NSRoundingMode 的類型

typedef NS_ENUM(NSUInteger, NSRoundingMode) {
    NSRoundPlain,   // Round up on a tie
    NSRoundDown,    // Always down == truncate
    NSRoundUp,      // Always up
    NSRoundBankers  // on a tie round so last digit is even
};

NSRoundPlain 是四舍五入
NSRoundDown 是向下取整
NSRoundUp 是向上取整
NSRoundBankers 是在四舍五入的基礎(chǔ)上，加上末尾數(shù)為5時(shí)绢慢，變成偶數(shù)的規(guī)則

一：四舍五入

// 四舍五入
    NSDecimalNumberHandler *roundPlain = [NSDecimalNumberHandler decimalNumberHandlerWithRoundingMode:NSRoundPlain scale:2 raiseOnExactness:NO raiseOnOverflow:NO raiseOnUnderflow:NO raiseOnDivideByZero:YES];
    {
        NSString *addStr = @"1.0";
        NSString *oneStr = @"1.114";
        NSString *twoStr = @"1.116";
        NSDecimalNumber *oneNum = [NSDecimalNumber decimalNumberWithString:oneStr];
        NSDecimalNumber *twoNum = [NSDecimalNumber decimalNumberWithString:twoStr];
        NSDecimalNumber *addNum = [NSDecimalNumber decimalNumberWithString:addStr];
        
        // 加法
        oneNum = [oneNum decimalNumberByAdding:addNum withBehavior:roundPlain];
        twoNum = [twoNum decimalNumberByAdding:addNum withBehavior:roundPlain];
        NSLog(@"\n1.114 + 1.0 （保留兩位小數(shù)）四舍五入的結(jié)果為:%@\n1.116 + 1.0 （保留兩位小數(shù)）四舍五入的結(jié)果為:%@", oneNum, twoNum);
    }

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二：向下取整

    // 向下取整
    NSDecimalNumberHandler *roundDown = [NSDecimalNumberHandler decimalNumberHandlerWithRoundingMode:NSRoundDown scale:2 raiseOnExactness:NO raiseOnOverflow:NO raiseOnUnderflow:NO raiseOnDivideByZero:YES];
    {
        NSString *subtractStr = @"1.0";
        NSString *oneStr = @"1.114";
        NSString *twoStr = @"1.116";
        NSDecimalNumber *oneNum = [NSDecimalNumber decimalNumberWithString:oneStr];
        NSDecimalNumber *twoNum = [NSDecimalNumber decimalNumberWithString:twoStr];
        NSDecimalNumber *subtractNum = [NSDecimalNumber decimalNumberWithString:subtractStr];
        
        // 減法
        oneNum = [oneNum decimalNumberBySubtracting:subtractNum withBehavior:roundDown];
        twoNum = [twoNum decimalNumberBySubtracting:subtractNum withBehavior:roundDown];
        NSLog(@"\n1.114 - 1.0 （保留兩位小數(shù)）向下取整的結(jié)果為:%@\n1.116 - 1.0 （保留兩位小數(shù)）向下取整的結(jié)果為:%@", oneNum, twoNum);
    }

2.png

三：向上取整

    // 向上取整
    NSDecimalNumberHandler *roundUp = [NSDecimalNumberHandler decimalNumberHandlerWithRoundingMode:NSRoundUp scale:2 raiseOnExactness:NO raiseOnOverflow:NO raiseOnUnderflow:NO raiseOnDivideByZero:YES];
    {
        NSString *multiplyStr = @"1.0";
        NSString *oneStr = @"1.114";
        NSString *twoStr = @"1.116";
        NSDecimalNumber *oneNum = [NSDecimalNumber decimalNumberWithString:oneStr];
        NSDecimalNumber *twoNum = [NSDecimalNumber decimalNumberWithString:twoStr];
        NSDecimalNumber *multiplyNum = [NSDecimalNumber decimalNumberWithString:multiplyStr];
        
        // 乘法
        oneNum = [oneNum decimalNumberByMultiplyingBy:multiplyNum withBehavior:roundUp];
        twoNum = [twoNum decimalNumberByMultiplyingBy:multiplyNum withBehavior:roundUp];
        NSLog(@"\n1.114 * 1.0 （保留兩位小數(shù)）向上取整的結(jié)果為:%@\n1.116 * 1.0 （保留兩位小數(shù)）向上取整的結(jié)果為:%@", oneNum, twoNum);
    }

3.png

四：NSRoundBankers

    // 在四舍五入的基礎(chǔ)上灿渴，加上末尾數(shù)為5時(shí)洛波，變成偶數(shù)的規(guī)則，例如小數(shù)點(diǎn)后兩位骚露， 1.215 時(shí)變?yōu)?1.22, 1.225 時(shí)變?yōu)?1.22
    NSDecimalNumberHandler *roundBankers = [NSDecimalNumberHandler decimalNumberHandlerWithRoundingMode:NSRoundBankers scale:2 raiseOnExactness:NO raiseOnOverflow:NO raiseOnUnderflow:NO raiseOnDivideByZero:YES];
    {
        NSString *dividStr = @"1.0";
        NSString *oneStr = @"1.115";
        NSString *twoStr = @"1.125";
        NSDecimalNumber *oneNum = [NSDecimalNumber decimalNumberWithString:oneStr];
        NSDecimalNumber *twoNum = [NSDecimalNumber decimalNumberWithString:twoStr];
        NSDecimalNumber *dividNum = [NSDecimalNumber decimalNumberWithString:dividStr];
        
        // 除法
        oneNum = [oneNum decimalNumberByDividingBy:dividNum withBehavior:roundBankers];
        twoNum = [twoNum decimalNumberByDividingBy:dividNum withBehavior:roundBankers];
        NSLog(@"\n1.115 / 1.0 （保留兩位小數(shù)）NSRoundBankers的結(jié)果為:%@\n1.125 / 1.0 （保留兩位小數(shù)）NSRoundBankers的結(jié)果為:%@", oneNum, twoNum);
    }

4.png