ccondon@ccondon-VirtualBox:~$ cat test2.c
#include <stdio.h>

int main() {
        long long x = -4337501956902748161LL;
        long long oldx;
        double oldd;
        while (x < 0L) {
                double *d = (double *)&x;
                if (*d > (double)x) {
                        printf("%lld\t%f\n", oldx, oldd);
                        printf("%lld\t%f\n", x, *d);
                        return 0;
                }
                oldd = *d;
                oldx = x;
                x -= 1LL;
        }
}
ccondon@ccondon-VirtualBox:~$ ./a.out
-4337501956902952560	-4337501956902952960.000000
-4337501956902952561	-4337501956902952448.000000