Perhaps people could review the latest patch in view of the following.

1) Quote from Mark Dickinson msg75815

"I think this would be valuable for rapid prototyping
of an algorithm in Python before translating it into
C.  In particular, it might help with detecting some
common C code bugs involving undefined behaviour---for
example, overflow in signed-integer arithmetic."

2) issue1621 "Do not assume signed integer overflow behavior"

Perhaps this could be treated as purely experimental?  (This might have been suggested already, sorry if I've missed it). Whatever happens I'd be glad to help out if possible, the big asset I have compared to others is time as I only work part time.