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forth: make branching offsets 1 byte

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Those bytes, those precious bytes!
This commit is contained in:
Virgil Dupras 2020-03-11 19:52:49 -04:00
parent abdf2c8adc
commit ea5f33558a
2 changed files with 28 additions and 28 deletions
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44
apps/forth/dict.asm
View File

@ -51,19 +51,15 @@ doesWord:
push hl \ pop iy
jr compiledWord
; This word is followed by *relative* offset (to the cell's addr) to where to
; branch to. For example, The branching cell of "IF THEN" would contain 4. Add
; This word is followed by 1b *relative* offset (to the cell's addr) to where to
; branch to. For example, The branching cell of "IF THEN" would contain 3. Add
; this value to RS.
branchWord:
push de
ld l, (ix)
ld h, (ix+1)
ld e, (hl)
inc hl
ld d, (hl)
dec hl
or a ; clear carry
add hl, de
ld a, (hl)
call addHL
ld (ix), l
ld (ix+1), h
pop de
@ -78,8 +74,12 @@ cbranchWord:
ld a, h
or l
jr z, branchWord
; skip next 2 bytes
call skipRS
; skip next byte in RS
ld l, (ix)
ld h, (ix+1)
inc hl
ld (ix), l
ld (ix+1), h
jp exit
CBRANCH:
@ -527,17 +527,14 @@ CMP:
.dw CMP
IF:
.dw nativeWord
; Spit a conditional branching atom, followed by 2 empty bytes. Then,
; push the address of those 2 bytes on the PS. ELSE or THEN will pick
; them up and set their own address in those 2 bytes.
; Spit a conditional branching atom, followed by an empty 1b cell. Then,
; push the address of that cell on the PS. ELSE or THEN will pick
; them up and set the offset.
ld hl, (CMPDST)
ld de, CBRANCH
call DEinHL
push hl ; address of cell to fill
; For now, let's fill it with a reference to ABORT in case we have a
; malformed construct
ld de, ABORTREF
call DEinHL
inc hl ; empty 1b cell
ld (CMPDST), hl
jp exit
@ -551,11 +548,11 @@ ELSE:
pop de ; cell's address
ld hl, (CMPDST)
; also skip ELSE word.
inc hl \ inc hl \ inc hl \ inc hl
inc hl \ inc hl \ inc hl
or a ; clear carry
sbc hl, de ; HL now has relative offset
ex de, hl ; HL has branching cell
call DEinHL
ld a, l
ld (de), a
; Set IF's branching cell to current atom address and spit our own
; uncondition branching cell, which will then be picked up by THEN.
; First, let's spit our 4 bytes
@ -563,8 +560,7 @@ ELSE:
ld de, BRANCH
call DEinHL
push hl ; address of cell to fill
ld de, ABORTREF
call DEinHL
inc hl ; empty 1b cell
ld (CMPDST), hl
jp exit
@ -580,8 +576,8 @@ THEN:
; There is nothing to skip because THEN leaves nothing.
or a ; clear carry
sbc hl, de ; HL now has relative offset
ex de, hl ; HL has branching cell
call DEinHL
ld a, l
ld (de), a
jp exit
.db "RECURSE"

12
apps/forth/util.asm
View File

@ -99,9 +99,9 @@ HLPointsQUIT:
; to after null-termination.
compSkip:
call HLPointsNUMBER
jr z, .isNumOrBranch
jr z, .isNum
call HLPointsBRANCH
jr z, .isNumOrBranch
jr z, .isBranch
call HLPointsLIT
jr nz, .isWord
; We have a literal
@ -109,9 +109,13 @@ compSkip:
call strskip
inc hl ; byte after word termination
ret
.isNumOrBranch:
.isNum:
; skip by 4
inc hl \ inc hl
inc hl
; continue to isBranch
.isBranch:
; skip by 3
inc hl
; continue to isWord
.isWord:
; skip by 2