iOS开发中高精度数值(货币)计算

r囧r小猫 2022-07-16 13:10 271阅读 0赞

对知识的深入，很大程度上取决于需求。最近在做一个P2P金融理财类的APP,其中对数值精度的要求很高，使用浮点型和双精度型表示，不能达到规定的精度要求。于是，从网上搜索相关能使Objective-C表示并计算更高精度数值的方法，在为数不多的相关链接中，发现了苹果提供用于高精度金融货币交易计算的API(NSDecimalNumber)。当然，这解决了我工作中遇到的问题，现在整理分享给大家。

NSDecimalNumber继承于NSNumber。

\- (instancetype)initWithMantissa:(unsignedlonglong)mantissa exponent:(short)exponent isNegative:(BOOL)flag;

//mantissa：长整形；exponent：指数；flag：正负数        
    NSDecimalNumber * amount0 = [[NSDecimalNumber alloc] initWithMantissa:42 exponent:-2 isNegative:NO];//0.42
    NSDecimalNumber * amount1 = [[NSDecimalNumber alloc] initWithMantissa:42 exponent:-2 isNegative:NO];//-4200

\- (instancetype)initWithDecimal:(NSDecimal)dcm;

\- (instancetype)initWithString:(nullableNSString \*)numberValue;

\- (instancetype)initWithString:(nullableNSString \*)numberValue locale:(nullableid)locale;

//locale代表一种格式,对于这种格式可以参考一下例子去理解
    NSDictionary *locale0 = [NSDictionary dictionaryWithObject:@"," forKey:NSLocaleDecimalSeparator];    //以","当做小数点格式
    NSDecimalNumber * amount2 = [[NSDecimalNumber alloc] initWithString:@"42,68" locale:locale0];//42.68
    NSLocale *locale5 = [[NSLocale alloc] initWithLocaleIdentifier:@"fr_FR"];//法国数据格式,法国的小数点是','逗号
    NSDecimalNumber * amount3 = [[NSDecimalNumber alloc] initWithString:@"42.68" locale:locale5];//42.68

此外， NSDecimalNumber还提供了对应的类方法：

\+ (NSDecimalNumber \*)decimalNumberWithMantissa:(unsignedlonglong)mantissa exponent:(short)exponent isNegative:(BOOL)flag;

\+ (NSDecimalNumber \*)decimalNumberWithDecimal:(NSDecimal)dcm;

\+ (NSDecimalNumber \*)decimalNumberWithString:(nullableNSString \*)numberValue;

\+ (NSDecimalNumber \*)decimalNumberWithString:(nullableNSString \*)numberValue locale:(nullableid)locale;

以下是基本的算术方法：

加法

\- (NSDecimalNumber \*)decimalNumberByAdding:(NSDecimalNumber \*)decimalNumber;

减法

\- (NSDecimalNumber \*)decimalNumberBySubtracting:(NSDecimalNumber \*)decimalNumber;

乘法

\- (NSDecimalNumber \*)decimalNumberByMultiplyingBy:(NSDecimalNumber \*)decimalNumber;

除法

\- (NSDecimalNumber \*)decimalNumberByDividingBy:(NSDecimalNumber \*)decimalNumber;

幂次方

\- (NSDecimalNumber \*)decimalNumberByRaisingToPower:(NSUInteger)power;

指数

\- (NSDecimalNumber \*)decimalNumberByMultiplyingByPowerOf10:(short)power;

四舍五入运算

\- (NSDecimalNumber \*)decimalNumberByRoundingAccordingToBehavior:(nullableid <NSDecimalNumberBehaviors>)behavior;

\+ (instancetype)decimalNumberHandlerWithRoundingMode:(NSRoundingMode)roundingMode scale:(short)scale raiseOnExactness:(BOOL)exact raiseOnOverflow:(BOOL)overflow raiseOnUnderflow:(BOOL)underflow raiseOnDivideByZero:(BOOL)divideByZero;         roundingMode 要使用的舍入模式，有四种值： NSRoundUp, NSRoundDown, NSRoundPlain, and NSRoundBankers

scale 结果保留几位小数

raiseOnExactness 发生精确错误时是否抛出异常，一般为NO

raiseOnOverflow 发生溢出错误时是否抛出异常，一般为NO

raiseOnUnderflow 发生不足错误时是否抛出异常，一般为NO

raiseOnDivideByZero 被0除时是否抛出异常，一般为YES

NSDecimalNumberHandler * rounUp = [NSDecimalNumberHandler decimalNumberHandlerWithRoundingMode:NSRoundDown scale:1 raiseOnExactness:NO raiseOnOverflow:NO raiseOnUnderflow:NO raiseOnDivideByZero:YES];
    NSDecimalNumber *subtotalAmount = [NSDecimalNumber decimalNumberWithMantissa:4284 exponent:-2 isNegative:NO];
    NSDecimalNumber * roundUpAmount = [subtotalAmount decimalNumberByRoundingAccordingToBehavior:rounUp];

比较运算

\- (NSComparisonResult)compare:(NSNumber \*)decimalNumber;

NSDecimalNumber *count0 = [NSDecimalNumber decimalNumberWithString:@"41"];
    NSDecimalNumber *count1 = [NSDecimalNumber decimalNumberWithString:@"43"];
    NSComparisonResult result = [count0 compare:count1];
    if (result == NSOrderedAscending) {
          //41 < 43
    } else if (result == NSOrderedSame) {
          //41 == 43
    } else if (result == NSOrderedDescending) {
          //41 > 43
    }

欢迎交流学习，不足之处，敬请指正。