Re: AC_C_BIGENDIAN answers "universal" on powerpc-aix

[Erik de Castro Lopo]

Eric Blake wrote:

> The brokenness of AC_C_BIGENDIAN has been known for some time now, still
> without a patch.  At this point, any approach is better than none, so it
> might be worth posting your ideas.

I've been using the following for years in a couple of projects
and it works well for me. The only place it doesn't work well
is when people using the Apple compiler try to run my configure
script with the compiler trying to generate universal binaries
(which IMO is a completely ridiculous idea).

Cheers,
Erik

dnl @synopsis AC_C_FIND_ENDIAN
dnl
dnl Determine endian-ness of target processor.
dnl @version 1.1        Mar 03 2002
dnl @author Erik de Castro Lopo <erikd AT mega-nerd DOT com>
dnl
dnl Majority written from scratch to replace the standard autoconf macro 
dnl AC_C_BIGENDIAN. Only part remaining from the original it the invocation
dnl of the AC_TRY_RUN macro.
dnl
dnl Permission to use, copy, modify, distribute, and sell this file for any 
dnl purpose is hereby granted without fee, provided that the above copyright 
dnl and this permission notice appear in all copies.  No representations are
dnl made about the suitability of this software for any purpose.  It is 
dnl provided "as is" without express or implied warranty.

dnl Find endian-ness in the following way:
dnl    1) Look in <endian.h>.
dnl    2) If 1) fails, look in <sys/types.h> and <sys/param.h>.
dnl    3) If 1) and 2) fails and not cross compiling run a test program.
dnl    4) If 1) and 2) fails and cross compiling then guess based on target.

AC_DEFUN([AC_C_FIND_ENDIAN],
[AC_CACHE_CHECK(processor byte ordering, 
        ac_cv_c_byte_order,

# Initialize to unknown
ac_cv_c_byte_order=unknown

if test x$ac_cv_header_endian_h = xyes ; then

        # First try <endian.h> which should set BYTE_ORDER.

        [AC_TRY_LINK([
                #include <endian.h>
                #if BYTE_ORDER != LITTLE_ENDIAN
                        not big endian
                #endif
                ], return 0 ;, 
                        ac_cv_c_byte_order=little
                )]
                                
        [AC_TRY_LINK([
                #include <endian.h>
                #if BYTE_ORDER != BIG_ENDIAN
                        not big endian
                #endif
                ], return 0 ;, 
                        ac_cv_c_byte_order=big
                )]

        fi

if test $ac_cv_c_byte_order = unknown ; then

        [AC_TRY_LINK([
                #include <sys/types.h>
                #include <sys/param.h>
                #if !BYTE_ORDER || !BIG_ENDIAN || !LITTLE_ENDIAN
                        bogus endian macros
                #endif
                ], return 0 ;, 

                [AC_TRY_LINK([
                        #include <sys/types.h>
                        #include <sys/param.h>
                        #if BYTE_ORDER != LITTLE_ENDIAN
                                not big endian
                        #endif
                        ], return 0 ;, 
                                ac_cv_c_byte_order=little
                        )]
                                
                [AC_TRY_LINK([
                        #include <sys/types.h>
                        #include <sys/param.h>
                        #if BYTE_ORDER != LITTLE_ENDIAN
                                not big endian
                        #endif
                        ], return 0 ;, 
                                ac_cv_c_byte_order=little
                        )]

                )]

        fi

if test $ac_cv_c_byte_order = unknown ; then
        if test $cross_compiling = yes ; then
                # This is the last resort. Try to guess the target processor 
endian-ness
                # by looking at the target CPU type.    
                [
                case "$target_cpu" in
                        alpha* | i?86* | mipsel* | ia64*)
                                ac_cv_c_big_endian=0
                                ac_cv_c_little_endian=1
                                ;;
                        
                        m68* | mips* | powerpc* | hppa* | sparc*)
                                ac_cv_c_big_endian=1
                                ac_cv_c_little_endian=0
                                ;;
        
                        esac
                ]
        else
                AC_TRY_RUN(
                [[
                int main (void) 
                {       /* Are we little or big endian?  From Harbison&Steele.  
*/
                        union
                        {       long l ;
                                char c [sizeof (long)] ;
                        } u ;
                        u.l = 1 ;
                        return (u.c [sizeof (long) - 1] == 1);
                        }
                        ]], , ac_cv_c_byte_order=big, 
                        ac_cv_c_byte_order=unknown
                        )

                AC_TRY_RUN(
                [[int main (void) 
                {       /* Are we little or big endian?  From Harbison&Steele.  
*/
                        union
                        {       long l ;
                                char c [sizeof (long)] ;
                        } u ;
                        u.l = 1 ;
                        return (u.c [0] == 1);
                        }]], , ac_cv_c_byte_order=little, 
                        ac_cv_c_byte_order=unknown
                        )
                fi      
        fi

)
]

if test $ac_cv_c_byte_order = big ; then
        ac_cv_c_big_endian=1
        ac_cv_c_little_endian=0
elif test $ac_cv_c_byte_order = little ; then
        ac_cv_c_big_endian=0
        ac_cv_c_little_endian=1
else
        ac_cv_c_big_endian=0
        ac_cv_c_little_endian=0

        
AC_MSG_WARN([[*****************************************************************]])
        AC_MSG_WARN([[*** Not able to determine endian-ness of target 
processor.       ]])
        AC_MSG_WARN([[*** The constants CPU_IS_BIG_ENDIAN and 
CPU_IS_LITTLE_ENDIAN in  ]])
        AC_MSG_WARN([[*** src/config.h may need to be hand editied.             
       ]])
        
AC_MSG_WARN([[*****************************************************************]])
        fi

)# AC_C_FIND_ENDIAN



-- 
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Erik de Castro Lopo
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