2 - Forth Interest Group

1
: ?branch,
,
: <
0 IF 0 WHILE 0 UNTIL
( CASE )
last do-ZERO-EOUAL =
IF
ELSE
( CASE )
penult @ do-OUEDUP =
IF \ ?DUP O= IF I UNTIL I WHILE
-2 codes gap
do-QUEDUP-BRANCH-UNLESS-ZERO COMPILE,
ELSE
penult @ Go-ZERO-EOUAL =
IF \ o= o= IFIUNTILIWHILE
-2 codes gap
do-BRANCH-IF-ZERO COMPILE,
ELSE \ O= IF/ UNTIL1 WHILE
-1 codes gap
do-BRANCH-UNLESS-ZERO COMPILE,
( 0 ENDCASE ) THEN THEN
last @ do-DUP =
IF \ DUP IF I UNTIL I WHILE
-1 codes gap
do-DUP-BRANCH-IF-ZERO COMPILE,
ELSE
last @ do-LITERAL =
ANDIF
next 1 codes - @ 0=
THEN
IF \ 0 IFIUNTILI WHILE
-2 codes gap
do-BRANCH COMP ILE,
ELSE \ IF I UNTIL I WHILE
do-BRANCH-IF-ZERO COMPILE,
( 0 ENDCASE ) THEN THEN THEN
We wil optimize other things in ?branch,, but they wil all follow that pattern.
n < and n >, for a literal n, can be optimized with the following paradigm.
( CASE )
$- o=
IF
do-LESS EXECUTE
ELSE
last @ do-LITERAL =
IF
( CASE )
next 1 codes - @ 0=
IF \ O <
penult @ last !
-2 codes gap
do-NEGATIVE COMPILE,
Forth Dimensions 33 July 1995 August