3 ms·
Indeed. But I think the text of the article already agrees with you :)
by jsnell 9y ago
Indeed. But I think the text of the article already agrees with you :)
- rjsw 9y agoYes, you did write that you were just considering immediate values. I'm not sure that PDP-6 Lisp used tags though, MacLisp used BiBop to determine the type of an object so the entries in the type table corresponding to the special pointers would have contained the fixnum type.
- jsnell 9y agoThey were still writing up BIBOP as the new hotness in 1977, so I'm pretty sure this predates BIBOP by a decent margin. But it's a fair point that the encoding in PDP-6 LISP doesn't match what we'd think of as tagging today. They left the 0-pointer as a non-integer (probably that meant NIL), so the type test would have been done using two comparisons rather than a mask+compare.