FP consistency and -O2

[Stuart Reynolds <gcc at stuartreynoldsDOTnet>]

I'm having issues with the optimisation options. I get different 
floating point calculations depending on whether -O is set or not.
Is this a bug? It's certainly causing bugs for me.
If its not a bug, does anyone know if there a way of turning off all 
optimisations that change program semantics?

Cheers,
Stuart

Here's the offending code:
--------------
#include <iostream>
#include <iomanip>

/*
Run:

g++       format.cxx && a.out > format.txt
g++  -O2  format.cxx && a.out > format_O2.txt
diff format_O2.txt format.txt

Output differs. Same with -O and -O1
gcc (GCC) 3.2.2 20030222 (Red Hat Linux 3.2.2-5)
*/


using namespace std;

int main()
{
  static const float period = 2 * M_PI;
  static const float totsteps = 50.0; //per period     


  cout << setprecision(6) << setiosflags(ios::fixed | ios::showpoint);

  for ( int i=0 ; i < 1000; ++i )
  {
     float x = ( period * i ) / totsteps;   
     cout << i << '\t' << std::cos(x) << endl;
  }
  return 0;
}