Re: Confirmation my method is right.

[Eric Blake]

On 09/28/2010 08:22 AM, Dr. David Kirkby wrote:
> I have a header file (it's /usr/include/float.h) of an AIX system, which
> should contain:
>
> typedef unsigned short fprnd_t;
>
> but for some reason this, and a few other things seem to be undefined
> when gcc gets around to parsing it (I think it might be a gcc bug).

Have you reported this to the gcc folks?

> This problem comes from compiling the GNU Scientific Library on AIX,
> where the GSL developers say that gcc's float.h is being used in
> preference to the IBM's float.h, and whilst the system's float.h has
> this declaration, the gcc one does not.

Indeed this is the reason.  However, although it may be solvable by 
changing gcc's <float.h> use #include_next <float.h> to also pull in 
IBM's definitions, there is no standard that requires the existence of 
fprnd_t; therefore, you should always be checking for its existence and 
be prepared with a fallback whether or not gcc changes their <float.h>.

> typedef unsigned short fprnd_t;
>
>
> To check if fprnd_t is defined or not, can you confirm.
>
>
> 1) I need to add to configure.ac
>
> AC_CHECK_DECLS(fprnd_t,,,[#include <float.h>])

Get in the habit of proper m4 quoting:

AC_CHECK_DECLS([fprnd_t],,,[[#include <float.h>]])

(the last argument is double-quoted because it is a literal string with 
no m4 macro contents, and because it contains a # which can cause 
problems in various other macros when not double-quoted, even if 
AC_CHECK_DECLS is immune to those problems).

> 2) I need to add in a C file which will need this declaration.
>
> #infdef HAVE_DECL_FPRND_T
> typedef unsigned short fprnd_t;
> #endif

Yes, this is one valid approach.  Another equally valid approach is:

AC_CHECK_TYPE([fprnd_t], [], [AC_DEFINE([fprnd_t], [unsigned short],
  [replacement for a missing fprnd_t type])], [[#include <float.h>]])

at which point config.h already replaces things for you, for less work 
in your .c file.

--
Eric Blake   address@hidden    +1-801-349-2682
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