[Bf-committers] 64 bits CPU support

[Ton Roosendaal]

Hi,

Here's some essential info for those interested in testing 64 bits  
binaries;

Back in the nineties I ported & maintained a 64 bits Linux dec alpha  
version. We dropped this in 2001 or so... but the foundation for proper  
64 bits support in Blender is still there. It is likely though that new  
code was added that's not 64 bits compatible (yes, not allowed to put a  
pointer in an integer), that's all to clean up.

Apple is going to 64 bits in their next upgrade, will definitely check  
that out. For those interested to already work on it, there's one  
important coding rule to apply in blender:

-> the variable type "long" has been typedeffed to be either 32 or 64  
bits integer, depending pointer size.

So, if you want to do pointer arithmetic, or cast pointers to int, use  
a "long". Also use "long" in (DNA) structures, that gets mapped OK. And  
make sure longs and pointers are properly aligned (8 byte aligned) in  
structs that get saved in blender files.

This rule might have been gone lost in recent code... or not fully  
covered in makefiles or Scons. All work todo.

Oh, and hackish part in Blender needs to be checked; to map pointer  
values from 64 bits systems back to 32 bits ones (file load,  
readfile.c) there's a conversion that might need to be updated... right  
now it does: pointer_32 = (pointer_64>>3);
This assuming that address space on a 64 bits system doesn't start  
somewhere in the billions.

-Ton-

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Ton Roosendaal  Blender Foundation ton at blender.org  
http://www.blender.org