It would be cleaner to use a ptrdiff_t here, but unfortunately we can't because the ivar_offset field in the runtime metadata is an int so ivar offsets beyond 4GB will not work on LP64 platforms.
This probably isn't a limitation. If you have more than 4GB of ivars in one object, you've done something badly wrong and probably shouldn't be allowed to write code anymore.
theraven
ericwa