====== aPLib ======
aPLib ist eine Kompressionsbibliothek von Ibsen Software und legt ihren Fokus auf die Größe und Geschwindigkeit der Entpackroutine. Für den Amstrad CPC existiert mittlerweile eine durch verschiedene Personen (siehe Thread im CPCWiki Forum in den Links) optimierte Version des Entpackers.

====== Decompressor ======

<code asm 1>
; 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 
</code>

====== Links ======
  * aPLib von Ibsen Software - [[http://ibsensoftware.com/products_aPLib.html]]
  * Thread im CPCWiki Forum - [[http://www.cpcwiki.eu/forum/programming/aplib-decruncher-10-faster-)]]