standards/130067: Wrong numeric limits in system headers?

[Vaclav Haisman]

>Number:         130067
>Category:       standards
>Synopsis:       Wrong numeric limits in system headers?
>Confidential:   no
>Severity:       serious
>Priority:       medium
>Responsible:    freebsd-standards
>State:          open
>Quarter:        
>Keywords:       
>Date-Required:
>Class:          sw-bug
>Submitter-Id:   current-users
>Arrival-Date:   Tue Dec 30 22:40:01 UTC 2008
>Closed-Date:
>Last-Modified:
>Originator:     Vaclav Haisman
>Release:        6.3
>Organization:
SU SH
>Environment:
FreeBSD shell.sh.cvut.cz 6.3-PRERELEASE FreeBSD 6.3-PRERELEASE #0: Fri Jan 18 17:04:16 CET 2008     root at shell.sh.cvut.cz:/usr/obj/usr/src/sys/SHELL-SMP  i386
>Description:
There seems to be a problem with definition of long double limits on FreeBSD i386/6.x.

shell::wilx:~/packed_vector> echo | g++ -dD -E -  | sort | grep LDBL_MAX
#define __LDBL_MAX_10_EXP__ 4932
#define __LDBL_MAX_EXP__ 16384
#define __LDBL_MAX__ 1.1897314953572316e+4932L

shell::wilx:~/packed_vector> fgrep -rn LDBL_MAX /usr/include
[...]
/usr/include/machine/float.h:75:#define LDBL_MAX_EXP    16384
/usr/include/machine/float.h:76:#define LDBL_MAX        1.1897314953572317650E+4932L
/usr/include/machine/float.h:77:#define LDBL_MAX_10_EXP 4932
/usr/include/float.h:75:#define LDBL_MAX_EXP    16384
/usr/include/float.h:76:#define LDBL_MAX        1.1897314953572317650E+4932L
/usr/include/float.h:77:#define LDBL_MAX_10_EXP 4932

Notice the difference in definition of LDBL_MAX, the values in system
headers are tiny bit larger than that defined by GCC itself.

machine/float.h:76:#define LDBL_MAX        1.1897314953572317650E+4932L
float.h:76:#define LDBL_MAX                1.1897314953572317650E+4932L
GCC: __LDBL_MAX__                          1.1897314953572316e+4932L

A simple test shows the following:

shell::wilx:~/tmp> cat >longdouble.cxx
#include <iostream>
#include <limits>
#include <cfloat>

int
main ()
{
  typedef std::numeric_limits<long double> limits;
  std::cout << "max: " << limits::max () << "\n";
  std::cout << "__LDBL_MAX__: " << __LDBL_MAX__ << "\n";
  std::cout << "LDBL_MAX: " << LDBL_MAX << "\n";
}

shell::wilx:~/tmp> g++ -o longdouble longdouble.cxx

shell::wilx:~/tmp> ./longdouble
max: 1.18973e+4932
__LDBL_MAX__: 1.18973e+4932
LDBL_MAX: inf

This is on 6.3/i386. 7.1/AMD64 does not print inf for LDBL_MAX. I
think this is a bug in 6.x headers or in GCC 3.4.x that it
uses. LDBL_MAX should never result in "inf".

>How-To-Repeat:
#include <iostream>
#include <limits>
#include <cfloat>

int
main ()
{
  typedef std::numeric_limits<long double> limits;
  std::cout << "max: " << limits::max () << "\n";
  std::cout << "__LDBL_MAX__: " << __LDBL_MAX__ << "\n";
  std::cout << "LDBL_MAX: " << LDBL_MAX << "\n";
}

>Fix:


>Release-Note:
>Audit-Trail:
>Unformatted: