[CMake] [Insight-developers] 64 bit build detection

[Michael Jackson]

Just to follow up with this, according to Apple's Universal Porting  
guide when figuring out if the system is big or little endian you  
should NOT test for the type of processor but rather have something  
like the following:

#if !defined(__APPLE__)
#define HOST_BIGENDIAN @HOST_BIGENDIAN@
#else
#  if defined(__BIG_ENDIAN__)
#    define HOST_BIGENDIAN 1
#  elif  defined (__LITTLE_ENDIAN__)
#    define HOST_BIGENDIAN 0
#  else
#    error "Unknown HOST_BIGENDIAN!"
#  endif
#endif


And _now_ the hoarse is officially beaten..
_________________________________________________________
Mike Jackson                  mike.jackson at bluequartz.net
BlueQuartz Software                    www.bluequartz.net
Principal Software Engineer                  Dayton, Ohio



On Jun 14, 2009, at 4:05 PM, Michael Wild wrote:

> On Mac OS X one shouldn't do this kind of detection during configure  
> step, because as has been mentioned a single file can be compiled  
> multiple times for different architectures during one single  
> compiler invocation. The size of void* and even endianness can  
> change. It is preferable to have a central config.h.in (or similar)  
> containing something like this:
>
> #if defined(__APPLE__)
> #  if defined(__i386__)
> #    undef HAVE_64_BIT
> #    undef HAVE_BIG_ENDIAN
> #  elif defined(__ppc__)
> #    undef HAVE_64_BIT
> #    define HAVE_BIG_ENDIAN
> #  elif defined(__x86_64__)
> #    define HAVE_64_BIT
> #    undef HAVE_BIG_ENDIAN
> #  elif defined(__ppc64__)
> #    define HAVE_64_BIT
> #    define HAVE_BIG_ENDIAN
> #  else
>     // oops
> #    error "Unknown architecture!"
> #  endif
> #else
> #  cmakedefine HAVE_64_BIT
> #  cmakedefine HAVE_BIG_ENDIAN
> #endif
>
>
> On NOT APPLE platforms you do the normal thing in your CMakeLists.txt:
>
> if( NOT APPLE )
>  # check 64 bit
>  if( CMAKE_SIZEOF_VOID_P EQUALS 4 )
>    set( HAVE_64_BIT 0 )
>  else( CMAKE_SIZEOF_VOID_P EQUALS 4 )
>    set( HAVE_64_BIT 1 )
>  endif( CMAKE_SIZEOF_VOID_P EQUALS 4 )
>
>  # check endianness
>  include( TestBigEndian )
>  test_big_endian( HAVE_BIG_ENDIAN )
>  if( HAVE_BIG_ENDIAN )
>    set( HAVE_BIG_ENDIAN 1 )
>  else( HAVE_BIG_ENDIAN )
>    set( HAVE_BIG_ENDIAN 0 )
>  endif( HAVE_BIG_ENDIAN )
> endif( NOT APPLE )
>
> # configure config.h
> configure_file( ${CMAKE_SOURCE_DIR}/config.h.in ${CMAKE_BINARY_DIR}/ 
> config.h )
> include_directories( ${CMAKE_BINARY_DIR} )
>
>
> HTH
>
> Michael
>
> On 12. Jun, 2009, at 15:01, David Cole wrote:
>
>> CMake does not warn.
>> And actually, I think I have to back-track on my statement a little  
>> bit.
>>
>> Whether or not a TRY_COMPILE "works" for a multiple arch / config  
>> build
>> *depends* entirely on what you are trying to compile and what  
>> result you are
>> expecting to get out of it. If you do a try compile on some code to  
>> detect
>> the presence of a function, for example, that should work fine on a
>> universal binary build (presuming the function you're trying to  
>> link against
>> is present in universal binary form in the library it lives in...).
>>
>> The thing that won't work on a multiple arch/config build is trying  
>> to
>> detect the size of something or the presence/absence of something  
>> where the
>> thing you're trying to measure is different in the different archs /
>> configs. If it's uniform across all archs/configs then you can  
>> measure it
>> and get an answer that makes sense for all archs/configs. If not,  
>> then you
>> can't.
>>
>> Does that make sense?
>>
>> So... CMake does not warn because it does not know whether what you  
>> are
>> attempting to measure is valid or not. It's up to you to "do the  
>> right
>> thing" in these sorts of situations.
>>
>> You already know that if you are building a universal binary with  
>> both
>> 32-bit and 64-bit architectures in it that it makes no sense to  
>> "measure"
>> the size of "void*" at CMake time. You know this because you know  
>> there is
>> more than one answer depending on which one runs.
>>
>>
>> Hope this clarifies things even further, (rather than muddying  
>> anybody's
>> waters...)
>>
>> David
>>
>>
>> On Thu, Jun 11, 2009 at 6:56 PM, Sean McBride <sean at rogue-research.com 
>> >wrote:
>>
>>> On 6/11/09 5:25 PM, David Cole said:
>>>
>>>> TRY_COMPILE works fine for cross compiles, just not for *mutiple
>>>> configs/architectures "simultaneously"* compiles...
>>>
>>> Thanks for the clarification, that language is clearer.
>>>
>>> Does CMake detect and warn in such cases?  (it is after all the  
>>> common
>>> case on OS X.)
>>>
>>> Cheers,
>>>
>>> --
>>> ____________________________________________________________
>>> Sean McBride, B. Eng                 sean at rogue-research.com
>>> Rogue Research                        www.rogue-research.com
>>> Mac Software Developer              Montréal, Québec, Canada
>>>
>>>
>>>
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