Hello.
The f128 suffix worked. Based on all the corrections you all pointed
out, I have created another patch. I think I took most of the things
under consideration but please mention if I missed anything. The
following test cases were inspected with this patch. I am not sure if
the second test case is supposed to be carried out like I did.

Thanks,
-Tejas

/* { dg-do link } */

extern int link_error (int);

#define TEST(FN, VALUE, RESULT) \
  if (__builtin_##FN (VALUE) != RESULT) link_error (__LINE__);

int
main (void)
{
  TEST(roundeven,  0, 0);
  TEST(roundeven,  0.5, 0);
  TEST(roundeven,  -0.5, 0);
  TEST(roundeven,  6, 6);
  TEST(roundeven,  -8, -8);
  TEST(roundeven,  2.5, 2);
  TEST(roundeven,  3.5, 4);
  TEST(roundeven,  -1.5, -2);
  TEST(roundeven,  3.499, 3);
  TEST(roundeven,  3.501, 4);

  return 0;
}

second test case :

/* { dg-do link } */
/* { dg-add-options float128 } */
/* { dg-require-effective-target float128 } */

extern int link_error (int);

#define TEST(FN, VALUE, RESULT) \
  if (__builtin_##FN (VALUE) != RESULT) link_error (__LINE__);

int
main (void)
{
  TEST(roundevenf128,  (0x1p64+0.5), (0x1p64));

  return 0;
}

On Fri, 31 May 2019 at 15:41, Martin Jambor <mjambor@suse.cz> wrote:
>
> On Thu, May 30 2019, Segher Boessenkool wrote:
> > On Thu, May 30, 2019 at 07:08:45PM +0200, Martin Jambor wrote:
> >> Interesting, I was also puzzled for a moment.  But notice that:
> >>
> >> int main ()
> >> {
> >>     _Float128 x = 18446744073709551617.5f128;
> >>     _Float128 y = __builtin_roundf128 (x);
> >> }
> >>
> >> behaves as expected... the difference is of course the suffix pegged to
> >> the literal constant (see
> >> https://gcc.gnu.org/onlinedocs/gcc-9.1.0/gcc/Floating-Types.html).
> >>
> >> I would also expect GCC to use a larger type if a constant does not fit
> >> into a double, but apparently that does not happen.  I would have to
> >> check but it is probably the right behavior according to the standard.
> >
> > 6.4.4.2/4: "An unsuffixed floating constant has type double."  I don't
> > think your suggestion would be okay?
>
> Sorry if I was not clear but I was definitely not suggesting that we
> change this (or anything).  I wrote that I was also surprised but
> believed that GCC was doing the correct thing.
>
> Thanks for pointing out where exactly the standard says what has to be
> done though.
>
> Martin