Coucou FX,
On Sat, 5 Mar 2011, FX wrote:
uintmax_t is the largest of the standard unsigned C types, so it cannot be
larger than unsigned long long.
That's a gcc property then. The C99 standard only guarantees that
uintmax_t is at least as large as unsigned long long, but it is allowed to
be some other larger type:
"The following type designates an unsigned integer type capable of
representing any value of any unsigned integer type: uintmax_t"
On x86_64, for example:
#include <stdio.h>
#include <stdint.h>
int main (void)
{
printf ("%lu ", sizeof (uintmax_t));
printf ("%lu ", sizeof (int));
printf ("%lu ", sizeof (long int));
printf ("%lu ", sizeof (long long int));
printf ("%lu\n", sizeof (__int128));
}
gives : 8 4 8 8 16
I am not sure how legal that is. __int128 is an extended signed integer
type, and thus the statement about intmax_t should apply to it as well. So
gcc is just pretending that __int128 is not really there.
Is __builtin_clzll available on all platforms?
Yes, we emit calls to this built-in unconditionally in the Fortran
front-end, and it has caused no trouble.
Thank you, that's the best guarantee I could ask for about the existence
of __builtin_clzll.
--
Marc Glisse
