On Tue, Jan 25, 2022 at 09:05:55AM +0100, FX wrote:
>
> > Got the following in testsuite/gfortran/gfortran.log
> >
> > NaN 7FFFA000000000000000
> > NaN 7FFFC000000000000000
> > NaN 7FFFA000000000000000
> >
Could be a problem with __builtin_nansl().
#include <stdio.h>
#include <stdint.h>
int
main(void)
{
union { float x; uint32_t i; } f;
union { double x; uint64_t i; } d;
union { long double x; uint64_t i[2]; } l;
printf("Quiet NaN\n");
f.x = __builtin_nanf("");
printf("%f %x\n", f.x, f.i);
d.x = __builtin_nan("");
printf("%lf %lx\n", d.x, d.i);
l.x = __builtin_nanl("");
printf("%Lf %lx%lx\n", l.x, l.i[1], l.i[0]);
printf("Signaling NaN\n");
f.x = __builtin_nansf("");
printf("%f %x\n", f.x, f.i);
d.x = __builtin_nans("");
printf("%lf %lx\n", d.x, d.i);
l.x = __builtin_nansl("");
printf("%Lf %lx%lx\n", l.x, l.i[1], l.i[0]);
return 0;
}
% ~/work/x/bin/gcc -o z a.c && ./z
Quiet NaN
nan 7fc00000
nan 7ff8000000000000
nan 7fffc000000000000000
Signaling NaN
nan 7fa00000
nan 7ff4000000000000
nan 7fffa000000000000000
s bit is 0, so the 7 is correct. The width of the
exponet is w = 8, 11, and 15 bits for float, double,
and long double. The first significant bit, d, is
then 9, 12, and 16.
s|----w---|d
7fc --> 0111 1111 1100
7fa --> 0111 1111 1010
s|-----w-----| d
7ff8 --> 0111 1111 1111 1000
7ff4 --> 0111 1111 1111 0100
s|-------w--------| d
7fffc -> 0111 1111 1111 1111 1100 <-- should be 7fff8?
7fffa -> 0111 1111 1111 1111 1010 <-- should be 7fff4?
What does linux/darwin show?
--
Steve
