C floating point & fsetround(FE_DOWNWARD) question

[Jon Grimm <jgrimm2@xxxxxxxxxx>]

Hi there.  Executing the following program compiled with ppc64-unknown-linux gcc::

include <stdio.h>
#include <fenv.h>

int main()
{
 int x=1023, y=1023;
 double z;

 fesetround(FE_DOWNWARD);
 z = (double)(x-y);
 printf ("z = %e\n", z);

 return 0;
}




If I compile this as 32-bit (-m32) I get a result of:

z = -0.000000e+00

But compiling for 64-bit (-m64):

z = 0.000000e+00

I'm trying to figure out whether one of these is incorrect, or either result is fine with regards to C99 or other relevant standards' expectations?   


Thanks,
Jon