[GRASS-dev] configure: testing arch endian

[Brad Douglas]

On Mon, 2006-05-08 at 14:48 +1200, Hamish wrote:
> > I would like to add a macro into aclocal.m4/configure.in to test for
> > architecture byte order.  This would then define something like
> > G_BIGENDIAN 0/1 in include/config.h.in.
> > 
> > I think this would be better than testing for it constantly with
> > G_is_little_endian().
> 
> what's so bad about that? If it's in a loop or somewhere where it will
> be a performance hit just save the result to a variable at the start of
> the module.

In the interest of simplification and code reduction...

> > This would also keep it from being reimplemented
> > in libraries that are not interdependent (eg. lib/gis,
> > lib/vector/dglib).
> > 
> > I noticed that endian is not even considered in lib/image.  I'll fix
> > that if I get the clear for the above (or some reversion of).
> > 
> > Comments?  Caveats?
> 
> what about the case of "universal" binaries on OSX, where the endianness
> at run time is not necessarily the endianness at configure/compile time?

http://developer.apple.com/documentation/Porting/Conceptual/PortingUnix/compiling/chapter_4_section_3.html

According to Apple, we should be including <endian.h> and test
__BIG_ENDIAN or __LITTLE_ENDIAN.  That's even simpler.  Everything is
handled by the '--host=', '--build=', and '--target=' configure
switches.

Maybe change G_is_little_endian() to something like this?
{
#ifdef __LITTLE_ENDIAN
    return 1;
#elif __BIG_ENDIAN
    return 0;
#else /* probably redundant case */
    return -1;
#endif
}


-- 
Brad Douglas <rez touchofmadness com>                      KB8UYR
Address: 37.493,-121.924 / WGS84    National Map Corps #TNMC-3785