egcs 1.0.3 bug in comparing doubles

[Olaf Lenzmann <lenzmann at bned dot com>]

Hello!

I encountered the following SEVERE bug w/ egcs (gcc version egcs-2.90.29
980515) on Linux
RedHat5.1. When compiling the attached source with "gcc mtest.cc -lm
-lstdc++" the result of
the first comparison is falsely considered false.


Olaf Lenzmann

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#include <stdio.h>
#include <math.h>
#include <iostream.h>

double snapToGrid(double value, double atomic)
{
  if( atomic == 0.0 )
    return value;

  double remainder = fmod(value, atomic);

  // Which direction?
  if(remainder < 0.5*atomic)
    return value - remainder;
  else
    return value + atomic - remainder;
}

int main (void) {
  double a = 6.375e-10;
  double b = 6.375e-10;
  double grid = 1.25e-11;

  if( snapToGrid(a, grid) == snapToGrid(b, grid) )
    cout << "Function calls yield equal result" << endl;

  double aResult = snapToGrid(a, grid);
  double bResult = snapToGrid(b, grid);

  if( aResult == bResult )
    cout << "Variables yield equal result" << endl;
}