2 - Forth Interest Group

( 0 ENDCASE ) THEN THEN THEN
; IMMEDIATE
The arithmetic operators should all receive optimization.
(Optimize: x n + x + n + 0 + n + )
: +
( CASE )
STATE @ 0=
IF
do-PLUS EXECUTE
ELSE
last @ do-LITERAL =
IF
( CASE )
penult @ do-LITERAL =
ORIF penult k do-LITERAL-PLUS = THEN
IF \ x n t or x + n t
0 last !
next 1 codes - @ next 3 codes - @ +
-4 codes gap
DUE' 9RIF penult @ do-LITERAL = THEN
IF
penult COMPILE,
ELSE
r
ELSE DROP THEN
next 1 codes - @o=
IF \ a +
penult @ last !
0 penult !
-2 codes gap
ELSE \ n t
penult @ last !
next 1 codes - @
-2 codeg gap
do-LITERAL-PLUS COMPILE,
I
( 0 ENDCASE ) THEN THEN
ELSE \ +
do-PLUS COMPILE,
( 0 ENDCASE ) THEN THEN
; IMMEDIATE
Pinhole optimization, like any form of peephole optimization, should work across uses of POSTPONE.
Given the definition,
: UNLESS 0 POSTPONE LITERAL POSTPONE = POSTPONE IF ; IMMEDIATE
when UNLESS is used, POSTPONE = should combine with the result of the preceding 0 POSTPONE LITERAL
to yield 0=, and then POSTPONE IF should yield the BRANCH-UNLESS-ZERO optimization.
Forth Dimensions 35 July 1995 August