为什么在GCC中-fidiprocal-math不安全？ [英] Why is -freciprocal-math unsafe in GCC?

问题描述

  -freciprocal-math 在GCC中改变了以下代码：双a = b / c; 
  

至

  double tmp = 1 / c; 
 double a = b * tmp; 
  

在GCC手册中，据说这样的优化是不安全的，不符合IEEE标准。但我想不出一个例子。你能举个例子吗？

解决方案

除以10并乘以0.1000000000000000055511151231257827021181583404541015625不一样。

-freciprocal-math in GCC changes the following code

double a = b / c;

to

 double tmp = 1/c;
 double a = b * tmp;

In GCC manual, it's said that such an optimization is unsafe and is not sticked to IEEE standards. But I cannot think of an example. Could you give an example about this?

解决方案

Dividing by 10 and multiplying by 0.1000000000000000055511151231257827021181583404541015625 are not the same thing.

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