[Python-Dev] 64 bit units in PyLong

[Siyuan Ren]

The current PyLong implementation represents arbitrary precision integers
in units of 15 or 30 bits. I presume the purpose is to avoid overflow in
addition , subtraction and multiplication. But compilers these days offer
intrinsics that allow one to access the overflow flag, and to obtain the
result of 64 bit multiplication as a 128 bit number. Or at least on x86-64,
which is the dominant platform.  Any reason why it is not done? If it is
only because no one bothers, I may be able to do it.
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