[Python-Dev] Performance (non)optimization: 31-bit ints in pointers

Tim Peters tim.one@comcast.net
Mon, 12 Aug 2002 20:44:46 -0400

[Jeff Epler]
> Many Lisp interpreters use 'tagged types' to, among other things, let
> small ints reside directly in the machine registers.

And many Lisp interpreters derive from ones written for once-trendy Lisp
hardware, which had special support for tag bits.  Simulating this in
software is a PITA.

> (due to alignment requirements on all common machines, all valid
> pointers-to-struct have 0 in their low bit)

Not so on word-addressed machines, though, or on machines using low-order
pointer bits for their own notion of tag bits.

patiently-awaiting-seymour-cray's-resurrection-ly y'rs  - tim