isnan的源代码在哪里？ [英] Where is the source code for isnan?

问题描述

由于标准的层次，c ++的include文件是一个老鼠巢。我试图找出实际调用的 __ isnan ，并且找不到具有实际定义的任何地方。

所以我只是用-S编写来看看程序集，如果我写：

  #include< ieee754.h> 
 
 void f（double x）{
 if（__isinf（x）... 
 
 if（__isnan（x））... 
 } 
  

这两个例程都被调用，我想看到实际的定义，可能会重构事情像这样是内联的，因为它应该只是一个比较，虽然当这个值在一个浮点寄存器中时很难实现。

无论如何或者不是一个好主意，问题是：WHERE是 __ isnan（x）的源代码

解决方案

Glibc在 sysdeps 文件夹，它支持的每个系统。你正在寻找的是一个 sysdeps / ieee754 / dbl-64 / s_isnan.c 我发现这个与 git grep __isnan 。

（虽然C ++头文件）包含模板的代码，C库中的函数不会，您必须查看glibc或任何一个。）

Because of the layers of standards, the include files for c++ are a rats nest. I was trying to figure out what __isnan actually calls, and couldn't find anywhere with an actual definition.

So I just compiled with -S to see the assembly, and if I write:

#include <ieee754.h>

void f(double x) {
  if (__isinf(x) ...

  if (__isnan(x)) ...
}

Both of these routines are called. I would like to see the actual definition, and possibly refactor things like this to be inline, since it should be just a bit comparison, albeit one that is hard to achieve when the value is in a floating point register.

Anyway, whether or not it's a good idea, the question stands: WHERE is the source code for __isnan(x)?

解决方案

Glibc has versions of the code in the sysdeps folder for each of the systems it supports. The one you’re looking for is in sysdeps/ieee754/dbl-64/s_isnan.c. I found this with git grep __isnan.

(While C++ headers include code for templates, functions from the C library will not, and you have to look inside glibc or whichever.)

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