collapseos/blk/398
Virgil Dupras ed2b91411a Limit ourselves to 8-bit branching
I'm planning on going back to 8-bit branching. 16-bit br cells incur
a non-negligible penalty and, while at first 64 words (128 bytes
forward or backward) seemed a bit limiting, I now don't see why one
would ever construct such a big branch. It would be un-forthy.

Also, I looked at using BC instead of IY to hold IP and the transition
would be a lot easier with 8-bit branching.

In this commit, all I do is add overflow checks in IF. The mechanic
below doesn't change. I'll give myself some time to think it over so
that I avoid yet another back and forth.
2020-05-24 10:16:25 -04:00

14 lines
325 B
Plaintext

: IF ( -- a | a: br cell addr )
COMPILE (?br) H@ 2 ALLOT ( br cell allot )
; IMMEDIATE
: THEN ( a -- | a: br cell addr )
DUP H@ -^ _bchk SWAP ( a-H a ) !
; IMMEDIATE
: ELSE ( a1 -- a2 | a1: IF cell a2: ELSE cell )
COMPILE (br)
2 ALLOT
[COMPILE] THEN
H@ 2- ( push a. -2 for allot offset )
; IMMEDIATE