Juho Snellman  <jsnell@iki.fi> wrote:
+---------------
| Rob Warnock <rpw3@rpw3.org> wrote:
| [... Python's tagging scheme ... ]
| > Preserving this useful characteristic on a 64-bit machine means
| > using a "three zero bits" lowtag for fixnums there, which is what
| > SBCL appears to have done.
| 
| Yes, that's one reason 64-bit SBCL has a different lowtag size. On the
| other hand, the unfinished CMUCL x86-64 port uses two zeroes lowtag
| for fixnums, just like the x86 CMUCL. I don't know why that decision
| was made.
+---------------

I'm not sure it *was* explicitly made. I suspect that (non)decision
might need to be revisited [to do it the SBCL way] before the CMUCL
x86-64 port gets finished, since the "fixnums index lispobjs" is so
heavily wired into CMUCL...


-Rob

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