> For the record, a Py_uintptr_t version works and has the same
> performance. Would you agree to it or is there still some menacing 
> oddity from the i386 days lurking around?

Technically, it's still dodgy:  as the gcc manual notes in:

http://gcc.gnu.org/onlinedocs/gcc/Arrays-and-pointers-implementation.html#Arrays-and-pointers-implementation

". That is, one may not use integer arithmetic to avoid the undefined behavior of pointer arithmetic as proscribed in C99 6.5.6/8."

I can't see as much scope for problems with the uintptr_t version.  But just because I can't anticipate the problems, it doesn't mean they don't exist.

It really would be better to avoid the undefined behaviour if at all possible.