From: FX <fxcoudert@gmail.com>
To: gcc@gcc.gnu.org, marc.glisse@inria.fr
Subject: Re: __builtin_clzll and uintmax_t
Date: Sat, 05 Mar 2011 22:05:00 -0000 [thread overview]
Message-ID: <AC5CE0DC-41F9-4DD2-86C4-91C92C5FE222@gmail.com> (raw)
Salut Marc !
> We have a variable of type uintmax_t and want to count the leading zeros. Can we just call __builtin_clzll on it?
Yes.
> In particular, can uintmax_t be larger than unsigned long long in gcc?
uintmax_t is the largest of the standard unsigned C types, so it cannot be larger than unsigned long long. 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
> 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.
FX
next reply other threads:[~2011-03-05 22:05 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
2011-03-05 22:05 FX [this message]
2011-03-06 8:57 ` Marc Glisse
2011-03-06 14:52 ` Jakub Jelinek
2011-03-08 12:04 ` Joern Rennecke
-- strict thread matches above, loose matches on Subject: below --
2011-03-05 21:05 Marc Glisse
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