C IEEE-Floats inf等于inf [英] C IEEE-Floats inf equal inf

问题描述

在C中，在IEEE-754浮点数的实现中，当我比较两个NaN的浮点数时，它返回0或false。但为什么两个浮点数都相等呢？

这个程序打印出equal：...（至少在Linux下，使用gcc的AMD64），在我看来它应该打印出不同的：... / p>

  #include< stdio.h> 
 #include< stdlib.h> 
 
 int main（void）
 {
 volatile double a = 1e200; //使用volatile来抑制编译器警告
 volatile double b = 3e200; 
 volatile double c = 1e200; 
 double resA = a * c; // resA和resB应该由inf 
 double resB = b * c; 
 if（resA == resB）
 {
 printf（equal：％e *％e =％e =％e =％e *％e \\\
，a，c ，RESA，RESB，b，C）; 
} 
 else 
 {
 printf（different：％e *％e =％e！=％e =％e *％e \\\
，a，c ，resA，resB，b，c）; 
} 
 return EXIT_SUCCESS; 
 
 
 
 
 
 $ b另一个例子，为什么我认为inf和inf不一样，是：自然数和有理数都是无限的，但不一样。
 
那么，为什么inf == inf？
解决方案
 Infinities比较平等，因为这就是标准所说的。 5.11节比较谓词的细节：
 
lockquote 
 
无穷操作数的相同符号应该比较相等。  
 
 
 
In C, on a implementation with IEEE-754 floats, when I compare two floating point numbers which are NaN, it return 0 or "false". But why do two floating point numbers which both are inf count as equal? 

This Program prints "equal: ..." (at least under Linux AMD64 with gcc) and in my opinion it should print "different: ...".
#include <stdio.h>
#include <stdlib.h>

int main(void)
  {
    volatile double a = 1e200; //use volatile to suppress compiler warnings
    volatile double b = 3e200;
    volatile double c = 1e200;
    double resA = a * c;  //resA and resB should by inf
    double resB = b * c;
    if (resA == resB)
      {   
        printf("equal: %e * %e = %e = %e = %e * %e\n",a,c,resA,resB,b,c);
      }   
    else
      {   
        printf("different: %e * %e = %e != %e = %e * %e\n", a, c, resA, resB, b, c);
      }   
    return EXIT_SUCCESS;
  }
A other example, why I think inf is not the same as inf, is: the numbers of natural numbers and rational numbers, both are infinite but not the same.

So why is inf == inf?
解决方案
Infinities compare equal because that's what the standard says. From section 5.11 Details of comparison predicates:

  
Infinite operands of the same sign shall compare equal.


                        
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