aplib156b.asm

; Rutina optimizada en tamaño (156 bytes):

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

;hl = source
;de = dest

depack:		;di
		;push	iy
		;call	unsafedepack
		;pop	iy
		;ret

unsafedepack:   ld      ixl,128
apbranch1:      ldi
aploop0:        ld      ixh,1           ;LWM = 0
aploop:         call    ap_getbit
                jr      nc,apbranch1
                call    ap_getbit2
                jr      nc,apbranch2
                ld      bc,16
                call    ap_getbit2
                jr      nc,apbranch3
apget4bits:     call    ap_getbit2
                rl      c
                jr      nc,apget4bits
                ld      a,b
                jr      z,apwritebyte
                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
apwritebyte:    ld      (de),a          ;write a 0
                inc     de
                jr      aploop0
apbranch3:      ld      c,(hl)          ;use 7 bit offset, length = 2 or 3
                rr      c
                ret     z               ;if a zero is found here, it's EOF
                inc     hl
                ld      a,b
                adc     a,2
                push    hl
                push    bc
                pop     iy
                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
                push    bc
                pop     iy

                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

                push    iy
                pop     de
                jr      ap_finishup

ap_getbit:      ld      a,ixl
ap_getbit2:     add     a,a
                jr      nz,ap_endbit
                ld      a,(hl)
                inc     hl
                rla
ap_endbit:      ld      ixl,a
                ret

ap_getgamma:    ld      bc,1
ap_getgammaloop:call    ap_getbit
                rl      c
                rl      b
                call    ap_getbit2
                jr      c,ap_getgammaloop
                ret