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詳解iOS之關(guān)于double/float數(shù)據(jù)計(jì)算精度問(wèn)題

更新時(shí)間：2018年02月26日 09:02:27 作者：叫我大表弟吧

本篇文章主要介紹了iOS之關(guān)于double/float數(shù)據(jù)計(jì)算精度問(wèn)題，小編覺(jué)得挺不錯(cuò)的，現(xiàn)在分享給大家，也給大家做個(gè)參考。一起跟隨小編過(guò)來(lái)看看吧

1、我們的app有一個(gè)判斷，當(dāng)用戶(hù)輸入的值，小于等于剩余的余額時(shí)，給用戶(hù)彈窗，代碼不往下執(zhí)行

當(dāng)用戶(hù)輸入 0.01 時(shí)，po 一下的結(jié)果是：0.10000.... ，當(dāng)用戶(hù)的余額是0.01時(shí)，po一下網(wǎng)絡(luò)請(qǐng)求的返回結(jié)果是：0.009999...

當(dāng)用戶(hù)輸入 66.05時(shí)，po 一下的結(jié)果是：66.049999...，當(dāng)用戶(hù)的余額是66.05時(shí)，po一下網(wǎng)絡(luò)請(qǐng)求的返回結(jié)果是：66.049999...

所以，當(dāng)數(shù)據(jù)較大時(shí)，不會(huì)有影響，因?yàn)橛脩?hù)輸入的數(shù)據(jù)和網(wǎng)絡(luò)返回?cái)?shù)據(jù)都被變成了不精確的小值了；但是，當(dāng)數(shù)據(jù)較小時(shí)，用戶(hù)輸入的數(shù)據(jù)沒(méi)有被轉(zhuǎn)，網(wǎng)絡(luò)返回的數(shù)據(jù)被轉(zhuǎn)成了不精確的小值，導(dǎo)致用戶(hù)輸入永遠(yuǎn)大于網(wǎng)絡(luò)返回的數(shù)據(jù)，代碼無(wú)法往下執(zhí)行；

解決：使用 NSDecimalNumber 將float、double數(shù)據(jù)轉(zhuǎn)化成NSDecimalNumber 類(lèi)型的對(duì)象進(jìn)行 +、-、*、/計(jì)算，再取值。

- (double)DecimalNumber:(double)num1 num2:(double)num2 { 
   
  NSDecimalNumber *n1 = [NSDecimalNumber decimalNumberWithString:[NSString stringWithFormat:@"%f",num1]]; 
   
  NSDecimalNumber *n2 = [NSDecimalNumber decimalNumberWithString:[NSString stringWithFormat:@"%f",num2]]; 
   
  NSDecimalNumber *n3 = [n1 decimalNumberBySubtracting:n2]; 
   
  return n3.doubleValue; 
} 
// 調(diào)用： 
double result = [self DecimalNumber: 2.01 num2: 2]; // 結(jié)果為 0.01

其中：
decimalNumberBySubtracting: n1 - n2，返回 n1 - n2 的結(jié)果值
decimalNumberByMultiplyingBy：n1 * n2，
decimalNumberByDividingBy：n1 / n2，
decimalNumberByAdding：n1 + n2，
compare：比較 n1 和 n2，返回比較結(jié)果；

2、進(jìn)行數(shù)據(jù)的四舍五入獲得結(jié)果

- (NSString*)Rounding:(float)number afterPoint:(NSInteger)position 
{ 
  NSDecimalNumberHandler *handler = [NSDecimalNumberHandler decimalNumberHandlerWithRoundingMode: NSRoundPlain scale: position raiseOnExactness: NO raiseOnOverflow: NO raiseOnUnderflow:NO raiseOnDivideByZero: NO]; 
   
  NSDecimalNumber *floatDecimal = [[NSDecimalNumber alloc] initWithFloat: number]; 
   
  NSDecimalNumber *resultNumber = [floatDecimal decimalNumberByRoundingAccordingToBehavior:handler]; 
   
  return [NSString stringWithFormat:@"%@",resultNumber]; 
} 
// 調(diào)用： 
NSString *result = [self Rounding:8.00092 afterPoint:3]; // 結(jié)果為 8.001

其中，參數(shù)number是需要四舍五入的數(shù)據(jù)，position是小數(shù)點(diǎn)后保留的位數(shù)；

高精度要求

使用系統(tǒng)提供的NSDecimalNumber API進(jìn)行計(jì)算，最后轉(zhuǎn)換為字符串輸出顯示。NSDecimalNumber轉(zhuǎn)換方法：

#import "NSDecimalNumber+Y_Add.h"

@implementation NSDecimalNumber (Y_Add)

+ (NSDecimalNumber *)y_decimalNumberWithFloat:(float)value{
  
  return [self y_decimalNumberWithFloat:value scale:2];
}

+ (NSDecimalNumber *)y_decimalNumberWithFloat:(float)value scale:(short)scale{
  
  return [self y_decimalNumberWithFloat:value roundingMode:NSRoundBankers scale:scale];
}

+ (NSDecimalNumber *)y_decimalNumberWithFloat:(float)value roundingMode:(NSRoundingMode)roundingMode scale:(short)scale{
  
  return [[[NSDecimalNumber alloc] initWithFloat:value] y_decimalNumberHandlerWithRoundingMode:roundingMode scale:scale];
}

+ (NSDecimalNumber *)y_decimalNumberWithDouble:(double)value{
  
  return [self y_decimalNumberWithDouble:value scale:2];
}

+ (NSDecimalNumber *)y_decimalNumberWithDouble:(double)value scale:(short)scale{
  
  return [self y_decimalNumberWithDouble:value roundingMode:NSRoundBankers scale:scale];
}

+ (NSDecimalNumber *)y_decimalNumberWithDouble:(double)value roundingMode:(NSRoundingMode)roundingMode scale:(short)scale{
  
  return [[[NSDecimalNumber alloc] initWithFloat:value] y_decimalNumberHandlerWithRoundingMode:roundingMode scale:scale];
}
 
/**
 * <#Description#>
 *
 * @return <#return value description#>
 */
- (NSDecimalNumber *)y_decimalNumberHandler{
  
  return [self y_decimalNumberHandlerWithRoundingMode:NSRoundBankers scale:2];
}

- (NSDecimalNumber *)y_decimalNumberHandlerWithRoundingMode:(NSRoundingMode)roundingMode scale:(short)scale{
   NSDecimalNumberHandler *handler = [NSDecimalNumberHandler decimalNumberHandlerWithRoundingMode:roundingMode
                                               scale:scale
                                         raiseOnExactness:NO
                                          raiseOnOverflow:YES
                                         raiseOnUnderflow:YES
                                        raiseOnDivideByZero:YES];
  return [self decimalNumberByRoundingAccordingToBehavior:handler];
}
@end

普通精度要求

使用系統(tǒng)提供的數(shù)學(xué)運(yùn)算進(jìn)行計(jì)算，最后轉(zhuǎn)換為字符串輸出顯示。保留小數(shù)點(diǎn)后N位的方法：

/**
 * formatterNumber .00 小數(shù)點(diǎn)后兩位
 *
 * @param number <#number description#>
 *
 * @return <#return value description#>
 */
+ (NSString *)y_formatterNumber:(NSNumber *)number{
  
  return [self y_formatterNumber:number fractionDigits:2];
}

+ (NSString *)y_formatterNumber:(NSNumber *)number fractionDigits:(NSUInteger)fractionDigits{
    
  NSNumberFormatter *numberFormatter = [[NSNumberFormatter alloc] init];
  [numberFormatter setMaximumFractionDigits:fractionDigits];
  [numberFormatter setMinimumFractionDigits:fractionDigits];
  
  return [numberFormatter stringFromNumber:number];
}

以上就是本文的全部?jī)?nèi)容，希望對(duì)大家的學(xué)習(xí)有所幫助，也希望大家多多支持腳本之家。

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