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; C convention
.globl _ap_uncompress
; register call
;
; hl = source
; de = dest
.globl ap_uncompress
; The original Z80 decompressors for ApLib were written by Dan Weiss (Dwedit).
;
; aPPack decompressor
; original source by dwedit
; very slightly adapted by utopian
; optimized by Metalbrain
; this is to enable undocumented Z80 opcodes in SDCC assembler
.ez80
_ap_uncompress::
ld hl, #2
add hl, sp
ld e, (hl)
inc hl
ld d, (hl)
inc hl
ld a, (hl)
inc hl
ld h, (hl)
ld l, a
ap_uncompress::
ld ixl, #128
apbranch1:
ldi
aploop0:
ld ixh, #1 ;LWM = 0
aploop:
call ap_getbit
jr nc, apbranch1
call ap_getbit
jr nc, apbranch2
ld b, #0
call ap_getbit
jr nc, apbranch3
ld c, #16 ;get an offset
apget4bits:
call ap_getbit
rl c
jr nc, apget4bits
jr nz, apbranch4
ld a, b
apwritebyte:
ld (de), a ;write a 0
inc de
jr aploop0
apbranch4:
and a
ex de, hl ;write a previous byte (1-15 away from dest)
sbc hl, bc
ld a, (hl)
add hl, bc
ex de, hl
jr apwritebyte
apbranch3:
ld c, (hl) ;use 7 bit offset, length = 2 or 3
inc hl
rr c
ret z ;if a zero is encountered here, it is EOF
ld a, #2
adc a,b
push hl
ld iyh, b
ld iyl, c
ld h, d
ld l, e
sbc hl, bc
ld c, a
jr ap_finishup2
apbranch2:
call ap_getgamma ;use a gamma code * 256 for offset, another gamma code for length
dec c
ld a, c
sub ixh
jr z, ap_r0_gamma ;if gamma code is 2, use old r0 offset,
dec a
;do I even need this code?
;bc=bc*256+(hl), lazy 16bit way
ld b, a
ld c, (hl)
inc hl
ld iyh, b
ld iyl, c
push bc
call ap_getgamma
ex (sp), hl ;bc = len, hl=offs
push de
ex de, hl
ld a, #4
cp d
jr nc, apskip2
inc bc
or a
apskip2:
ld hl, #127
sbc hl, de
jr c, apskip3
inc bc
inc bc
apskip3:
pop hl ;bc = len, de = offs, hl=junk
push hl
or a
ap_finishup:
sbc hl, de
pop de ;hl=dest-offs, bc=len, de = dest
ap_finishup2:
ldir
pop hl
ld ixh, b
jr aploop
ap_r0_gamma:
call ap_getgamma ;and a new gamma code for length
push hl
push de
ex de, hl
ld d, iyh
ld e, iyl
jr ap_finishup
ap_getbit:
ld a, ixl
add a, a
ld ixl, a
ret nz
ld a, (hl)
inc hl
rla
ld ixl, a
ret
ap_getgamma:
ld bc, #1
ap_getgammaloop:
call ap_getbit
rl c
rl b
call ap_getbit
jr c, ap_getgammaloop
ret
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