The following test program tests inequality of two doubles, then equality. 
The bug is that both will hold if 
- compiled with optimization (-O1 is enough) 
- first, an int was shifted into the ostream 
 
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#include <iostream> 
#include <cmath> 
int main() 
{ 
	double dist1 = std::sqrt((2.0 - 6)*(2.0 - 6) + (2.0 - 1)*(2.0 - 1)); 
	double dist2 = std::sqrt((5.0 - 6)*(5.0 - 6) + (5.0 - 1)*(5.0 - 1)); 
	 
	if(dist1 != dist2) 
	{ 
		std::cerr << 1 // outputting any int here makes the bug show up 
				  << ((dist1 == dist2) ? "compiler broken\n" : ""); 
	} 
} 
---------------------------------------------- 
 
Executing 
  g++ -Wall -O1 double_comparison.cxx -o double_comparison && 
./double_comparison 
gives: 
  1compiler broken 
 
The bug was verified with 3.2.3 and 3.2, too. On 2.95.3, it does not show up. 
We tried to strip the program down as far as we could, hopefully you can shed light 
on this.