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Floating point problems (accuracy).


Hi
  We are having a few problems regarding floating point inaccuracies under
  Linux.  Please see the code below.

/*
NOTE:-  This code is an example which demonstrates the sort of problems
        we are getting.
*/
main()
{
  int i;
  double x;

  x = -5.765;
  i = x * 100000;
  printf("I = %d\n",i);

}

/*

We are porting code from a Sun Workstation to a Linux PC.  We have noticed
inaccuracies of double values on the Linux PC.  If we simply compile the
above program e.g "gcc t.c" when we run it we get -576499 when we were really
expecting -576500.  We discovered that if we specify some flags:-

 gcc -march=pentium4 -mfpmath=sse t.c

then suddenly the floating point values become more accurate (i.e. we get the 
value -576500) and other related problems go away (our results agree with the 
same tests running on the Sun).

These flags only seem to work on a pentium4 or an AMD-64, i.e the newer
processor chips.  We would have liked the solution to be more generic.

Does any one know a better way of fixing this?

What was the solution for the older processor chips?

Is there a generic solution?

Thanks for all your help

  Phil Prentice.


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