; aPPack decompressor 
; original source by dwedit
; very slightly adapted by utopian
; optimized by Metalbrain


;hl = source
;de = dest


depack:         ld      a, 128
apbranch1:      ldi
aploop2:        ld      ixh, 1
aploop:         add     a, a
                jr      z, ap1
                jr      nc, apbranch1
apnogetbit1:    add     a, a
                jr      z, ap2
                jr      nc, apbranch2
apnogetbit2:    add     a, a
                jr      z, ap3
                jr      nc, apbranch3
apnogetbit3:    ld      bc, 16           ;get an offset
apget4bits:     add     a, a
                jr      z, ap4
apnogetbit4:    rl      c
                jp      nc, apget4bits


                jr      nz, apbranch4
                ex      de, hl
                ld      (hl), b          ;write a 0
                ex      de, hl
                inc     de
                jp      aploop2


ap1:            ld      a, (hl)
                inc     hl
                rla
                jr      c, apnogetbit1
                jp      apbranch1


ap4:            ld      a, (hl)
                inc     hl
                rla
                jp      apnogetbit4


apbranch4:      ex      af, af'
                ex      de, hl          ;write a previous byte (1-15 away from dest)
                sbc     hl, bc
                ld      a, (hl)
                add     hl, bc
                ld      (hl), a
                ex      af, af'
                ex      de, hl
                inc     de
                jp      aploop2


ap3:            ld      a, (hl)
                inc     hl
                rla
                jr      c, apnogetbit3
apbranch3:      ld      c, (hl)          ;use 7 bit offset, length = 2 or 3
                inc     hl
                ex      af, af'
                rr      c
                ret     z               ;if a zero is found here, it's EOF
                ld      a, 2
                ld      b, 0
                adc     a, b
                push    hl
                ld      iyh, b
                ld      iyl, c
                ld      h, d
                ld      l, e
                sbc     hl, bc
                ld      c, a
                ex      af, af'
                ldir
                pop     hl
                ld      ixh, b
                jp      aploop
ap2:            ld      a, (hl)
                inc     hl
                rla
                jr      c, apnogetbit2
apbranch2:      call    ap_getgamma     ;use a gamma code * 256 for offset, another gamma code for length
                dec     c
                ex      af, af'
                ld      a, c
                sub     ixh
                jr      z, ap_r0_gamma
                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_getgamma2


                ex      (sp), hl         ;bc = len, hl=offs
                push    de
                ex      de, hl


                ex      af, af'
                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
                sbc     hl, de
                ex      af, af'
                pop     de              ;hl=dest-offs, bc=len, de = dest
                ldir
                pop     hl
                ld      ixh, b
                jp      aploop


ap_r0_gamma:    call    ap_getgamma2    ;and a new gamma code for length
                push    hl
                push    de
                ex      de, hl


                ld      d, iyh
                ld      e, iyl
                sbc     hl, de
                pop     de              ;hl=dest-offs, bc=len, de = dest
                ldir
                pop     hl
                ld      ixh, b
                jp      aploop


ap5:            ld      a,(hl)
                inc     hl
                rla
                jp      apnogetbit5
ap6:            ld      a, (hl)
                inc     hl
                rla
                jp      apnogetbit6
ap7:            ld      a, (hl)
                inc     hl
                rla
                jp      apnogetbit7
ap8:            ld      a, (hl)
                inc     hl
                rla
                jp      apnogetbit8
ap9:            ld      a, (hl)
                inc     hl
                rla
                jp      apnogetbit9


ap10:           ld      a, (hl)
                inc     hl
                rla
                ret     nc 
                jp      ap_getgammaloop


ap_getgamma2:   ex      af, af'
ap_getgamma:    ld      bc, 1
                add     a, a
                jr      z, ap5
apnogetbit5:    rl      c
                add     a, a
                jr      z, ap6
apnogetbit6:    ret     nc
                add     a, a
                jr      z, ap7
apnogetbit7:    rl      c
                add     a, a
                jr      z, ap8
apnogetbit8:    ret     nc
ap_getgammaloop:add     a, a
                jr      z, ap9
apnogetbit9:    rl      c
                rl      b
                add     a, a
                jr      z, ap10
apnogetbit10:   ret     nc 
                jp      ap_getgammaloop