[MIT-Scheme-devel] tag bits

[Taylor R Campbell]

Currently, I believe the only objects whose addresses are not aligned
on word boundaries are compiled entries.  If we forced them to be
aligned, then the log_2 (bits per word) low-order bits of every object
address would be zero, and we could shift the address by that many
bits when storing it as an object's datum.

This would let us quadruple the usable virtual address space on 32-bit
systems, or octuple it if we got rid of the scode type tags and some
unused type tags too (using records instead or something) and reduced
the tags to five bits.

Probably more trouble than it's worth, but it's a cute thought
nevertheless which wouldn't require rewriting half of MIT Scheme.

(I still occasionally think about this because while some of you lucky
folks may be on super-snappy 64-bit machines, I'm still using a six-
year-old 32-bit laptop.)