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;Z80 Version by Dan Weiss
;Call depack.
;hl = source
;de = dest
ap_bits: .db 0
ap_byte: .db 0
lwm: .db 0
r0: .dw 0
ap_getbit:
push bc
ld bc,(ap_bits)
rrc c
jr nc,ap_getbit_continue
ld b,(hl)
inc hl
ap_getbit_continue:
ld a,c
and b
ld (ap_bits),bc
pop bc
ret
ap_getbitbc: ;doubles BC and adds the read bit
sla c
rl b
call ap_getbit
ret z
inc bc
ret
ap_getgamma:
ld bc,1
ap_getgammaloop:
call ap_getbitbc
call ap_getbit
jr nz,ap_getgammaloop
ret
depack:
;hl = source
;de = dest
ldi
xor a
ld (lwm),a
inc a
ld (ap_bits),a
aploop:
call ap_getbit
jp z, apbranch1
call ap_getbit
jr z, apbranch2
call ap_getbit
jr z, apbranch3
;LWM = 0
xor a
ld (lwm),a
;get an offset
ld bc,0
call ap_getbitbc
call ap_getbitbc
call ap_getbitbc
call ap_getbitbc
ld a,b
or c
jr nz,apbranch4
xor a ;write a 0
ld (de),a
inc de
jr aploop
apbranch4:
ex de,hl ;write a previous bit (1-15 away from dest)
push hl
sbc hl,bc
ld a,(hl)
pop hl
ld (hl),a
inc hl
ex de,hl
jr aploop
apbranch3:
;use 7 bit offset, length = 2 or 3
;if a zero is encountered here, it's EOF
ld c,(hl)
inc hl
rr c
ret z
ld b,2
jr nc,ap_dont_inc_b
inc b
ap_dont_inc_b:
;LWM = 1
ld a,1
ld (lwm),a
push hl
ld a,b
ld b,0
;R0 = c
ld (r0),bc
ld h,d
ld l,e
or a
sbc hl,bc
ld c,a
ldir
pop hl
jr aploop
apbranch2:
;use a gamma code * 256 for offset, another gamma code for length
call ap_getgamma
dec bc
dec bc
ld a,(lwm)
or a
jr nz,ap_not_lwm
;bc = 2?
ld a,b
or c
jr nz,ap_not_zero_gamma
;if gamma code is 2, use old r0 offset, and a new gamma code for length
call ap_getgamma
push hl
ld h,d
ld l,e
push bc
ld bc,(r0)
sbc hl,bc
pop bc
ldir
pop hl
jr ap_finishup
ap_not_zero_gamma:
dec bc
ap_not_lwm:
;do I even need this code?
;bc=bc*256+(hl), lazy 16bit way
ld b,c
ld c,(hl)
inc hl
ld (r0),bc
push bc
call ap_getgamma
ex (sp),hl
;bc = len, hl=offs
push de
ex de,hl
;some comparison junk for some reason
ld hl,31999
or a
sbc hl,de
jr nc,skip1
inc bc
skip1:
ld hl,1279
or a
sbc hl,de
jr nc,skip2
inc bc
skip2:
ld hl,127
or a
sbc hl,de
jr c,skip3
inc bc
inc bc
skip3:
;bc = len, de = offs, hl=junk
pop hl
push hl
or a
sbc hl,de
pop de
;hl=dest-offs, bc=len, de = dest
ldir
pop hl
ap_finishup:
ld a,1
ld (lwm),a
jp aploop
apbranch1:
ldi
xor a
ld (lwm),a
jp aploop
|
