Re: AC_TYPE_LONG_LONG_INT and AC_TYPE_UNSIGNED_LONG_LONG_INT (was: Re: [Bug-tar] GNU tar 1.19 on HP-UX)

[H.Merijn Brand]

On Sun, 21 Oct 2007 18:50:57 +0200, Bruno Haible <address@hidden> wrote:

> Hi Paul,
> 
> Paul Eggert wrote on 2007-10-16:
> > Thanks for verifying this.  I have started by installing the following
> > fix to Autoconf, and will follow up on gnulib shortly.
> > 
> > 2007-10-16  Paul Eggert  <address@hidden>
> > 
> >     Check for 64-bit int errors in HP-UX 10.20 preprocessor.
> 
> It exists also in the HP-UX 11.00 preprocessor.
> 
> >     Problem reported by H.Merijn Brand in
> >     <http://lists.gnu.org/archive/html/bug-tar/2007-10/msg00018.html>.
> >     * lib/autoconf/types.m4 (AC_TYPE_LONG_LONG_INT):
> >     (AC_TYPE_UNSIGNED_LONG_LONG_INT):
> >     Check that preprocessor handles 64-bit ints, too.
> 
> The effect is that one of these tests says yes, and the other says no.
> Using the stdint.h from gnulib, one then has this:
> 
> $ cat foo.c
> #include "config.h"
> #include <stdio.h>
> #include <stdint.h>
> uint64_t uu;
> int64_t ii;
> int main ()
> {
>   fprintf(stderr, "intmax_t size = %d\n", sizeof (intmax_t));
>   fprintf(stderr, "uintmax_t size = %d\n", sizeof (uintmax_t));
>   fprintf(stderr, "int64_t size = %d\n", sizeof (int64_t));
>   fprintf(stderr, "uint64_t size = %d\n", sizeof (uint64_t));
> }
> $ cc -Ae -O -I.. -I. foo.c libgnu.a 
> $ ./a.out 
> intmax_t size = 8
> uintmax_t size = 4
> int64_t size = 8
> uint64_t size = 8
> 
> Three things are not good here:
> 1) sizeof (uintmax_t) < sizeof (intmax_t).
> 2) sizeof (uintmax_t) < sizeof (uint64_t).
> 3) sizeof (uintmax_t) < 8.
> 
> 1) is bad because much code assumes that every signed int can be losslessly
>    casted into its corresponding unsigned counterpart. Also a lot of code
>    assumes that sizeof (uintmax_t) == sizeof (intmax_t).
>    One such code is gnulib's vasnprintf: it assumes that %jd and %ju take
>    as argument an integer of the same size. In this situation it does not do
>    so any more, and the unit test of the 'fprintf-posix' module fails.
> 
> 2) is bad because a lot code assumes that every unsigned scalar integer type
>    can be losslessly casted to uintmax_t.
> 
> 3) is bad because ISO C 99 requires the existence of an uint_least64_t type;
>    thus 64-bit types should be commonplace.
> 
> So the change fixed one problem but opened up three other problems.
> 
> What are the options?
> 
> A) Accept the fact that although 64-bit types may be known to the compiler,
>    they may not portably be used in preprocessor expressions.
>    This means:
>    - In the autoconf tests: undo the last change.
>    - In gnulib's stdint.h and inttypes.h: Compare the values of UINTMAX_MAX
>      etc. at configure time, rather than at compile time in the preprocessor.
> 
> B) Turn off the 64-bit types of HP-UX 11 cc.

That would be too generic. HP-UX 11.11 (11iv1) and 11.23 are much
more reliable in 64bit world than 11.00 and 10.20. 10.20 isn't
expected to do any 64bit issues correctly at all.

>    This means:
>    - Change AC_TYPE_LONG_LONG_INT so that it says "no" whenever
>      AC_TYPE_UNSIGNED_LONG_LONG_INT says "no".
>    - Add a "#define int64_t unusable_int64_t"
>      and   "#define uint64_t unusable_uint64_t"
>      to config.h, also as part of AC_TYPE_LONG_LONG_INT and
>      AC_TYPE_UNSIGNED_LONG_LONG_INT.
> 
> C) Some other option I'm missing?

I for sure would go for A).

-- 
H.Merijn Brand         Amsterdam Perl Mongers (http://amsterdam.pm.org/)
using & porting perl 5.6.2, 5.8.x, 5.10.x  on HP-UX 10.20, 11.00, 11.11,
& 11.23, SuSE 10.1 & 10.2, AIX 5.2, and Cygwin.       http://qa.perl.org
http://mirrors.develooper.com/hpux/            http://www.test-smoke.org
                        http://www.goldmark.org/jeff/stupid-disclaimers/