; 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_depack::
        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