Illustration of the effect of register allocation on floating-point numbers rounding depending on internal precision as described in "The pitfalls of verifying floating-point computations" by David Monniaux, section 3.1.1.

$ cat dummy.c 
void do_nothing(double *x __attribute ((unused))) {}
$ cat x87.c 
#include <assert.h>

void do_nothing(double *x);

int main(void)
{
        double x = 0x1p-1022, y = 0x1p100, z;
        do_nothing(&y);
        z = x/y;
        if (z != 0) {
                do_nothing(&z);
                assert(z != 0);
        }
        return 0;
}
$ cc -std=c99 -Wall -W -pedantic -mfpmath=387 -O1 -o x87 dummy.c x87.c
$ ./x87 
x87: x87.c:12: main: Assertion `z != 0' failed.
Aborted
$ cc -std=c99 -Wall -W -pedantic -mfpmath=sse -O1 -o x87 dummy.c x87.c
./x87
$

	Name	Last modified	Size	Description
	Parent Directory		-
	dummy.c	2011-01-13 20:01	53
	Makefile	2011-01-13 19:54	105
	x87.c	2011-01-13 19:49	200
	HEADER.html	2011-02-01 12:31	1.0K