JavaScript浮点好奇心 [英] JavaScript floating point curiosity

问题描述

我尝试做一些浮点比较，这里是我发现：

  130 === 130.000000000000014210854715 // true 
 130 === 130.000000000000014210854716 // false 
 9 === 9.0000000000000008881784197001 // true 
 9 === 9.0000000000000008881784197002 // false 
 0.1 === 0.100000000000000012490009027033 // true 
 0.1 === 0.100000000000000012490009027034 // false 
  

我试过在Firefox和Chrome上运行相同的结果。好吧，我知道浮点比较是一个坏的做法，有意想不到的行为。但我只是好奇那些数字，为什么或如何计算这些序列的小数位数？

如果你希望你甚至可以进一步扩展这些序列下一个序列）。

解决方案

小数部分超出JavaScript的 Number 类型的精度。 / p>

JavaScript只能处理您的号码的 130.0000000000000 部分，因此变为 code>（ 0 没有意义）。

每 在JavaScript中实际上是一个64位的 IEEE-754 浮动广告，因此 130.000000000000014210854715 将看起来像二进制...

  1000000011010000010000000000000000000000000000000000000000000000 
  

群组符号（ +



您可以看到数字<$ c $或$ c> 130 是相同的...

  0,10000000110,1000001000000000000000000000000000000000000000000 
  

您需要一个128位的 Number 要区分这两个数字，请使用 bignum JavaScript的实现。

I tried doing some floating point comparison and here is what I found:

130 === 130.000000000000014210854715 // true
130 === 130.000000000000014210854716 // false
9 === 9.0000000000000008881784197001 // true
9 === 9.0000000000000008881784197002 // false
0.1 === 0.100000000000000012490009027033 // true
0.1 === 0.100000000000000012490009027034 // false

I tried running those on Firefox and Chrome with the same results. Okay, I KNOW that floating point comparison is a bad practice and has unexpected behavior. But I just curious about those numbers, why or how does those sequence of fractional digits calculated?

If you wish you could even expand those sequence further (kind of binary searching for the next sequence).

解决方案

The fractional portion exceeds the precision of JavaScript's Number type.

JavaScript can only handle the 130.0000000000000 portion of your number, so it becomes 130 (those 0s have no significance).

Every Number in JavaScript is really a 64-bit IEEE-754 float, so the number 130.000000000000014210854715 will look like in binary...

0,10000000110,10000010000000000000000000000000000000000000000000000

Where the groups are sign (+ or -), exponent and significand/mantissa.

You can see that the number 130 is the same...

0,10000000110,10000010000000000000000000000000000000000000000000000 

You'd need a 128 bit Number for JavaScript to be able to tell these two numbers apart, ot use a bignum implementation for JavaScript.

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