浮点数0.2 + 0.1舍入误差 [英] floating point 0.2 + 0.1 rounding error

问题描述

可能重复:
JavaScript的数学运算是否被破坏?

Possible Duplicate:
Is JavaScript's Math broken?

我遇到了这个四舍五入的问题:

I came across this rounding issue:

当我这样做时:

 .2  + .1 results in 0.30000000000000004
 .7  + .1 results in 0.7999999999999999
1.1  + .1 results in 1.2000000000000002

以此类推...

任何人都可以(详细解释)为什么吗?可能是一些二进制四舍五入的东西.但是我真的很想知道会发生什么...

Can anyone explain (in detail) why? Probably some binary rounding stuff. But I like to really know what happens...

推荐答案

简而言之，因为.2实际上不是.2；它实际上是最接近的可表示双精度数，即

In a nutshell, because .2 isn't actually .2; it's actually the closest representable double-precision number, which is

0.200000000000000011102230246251565404236316680908203125.

类似地，.1确实是

0.1000000000000000055511151231257827021181583404541015625

将它们加在一起时，结果会再次四舍五入到最接近的可表示数字

When you add those together, the result is rounded again to the nearest representable number, which is

0.3000000000000000444089209850062616169452667236328125

最后，当您将其打印出来时，该数字将四舍五入为17位十进制数字，从而得到您观察到的结果.

Finally, when you print it out, that number gets rounded to 17 decimal digits, giving the result you observe.

您的其他示例遵循相同的模式.

Your other examples follow the same pattern.

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