From 30571429ade72a464b0fdb5e583893405959fb4c Mon Sep 17 00:00:00 2001
From: Peter Ferrie <peter.ferrie@gmail.com>
Date: Tue, 29 Nov 2016 17:21:58 -0800
Subject: [PATCH] how to make your own version

---
 APSRCDST.S | 231 +++++++++++++++++++++++++++++++++++++++++++++++++++++
 make.txt   |  15 ++++
 2 files changed, 246 insertions(+)
 create mode 100644 APSRCDST.S
 create mode 100644 make.txt

diff --git a/APSRCDST.S b/APSRCDST.S
new file mode 100644
index 0000000..2cd55ba
--- /dev/null
+++ b/APSRCDST.S
@@ -0,0 +1,231 @@
+;aPLib data decompressor for Apple II
+;Peter Ferrie (peter.ferrie@gmail.com)
+;assemble using ACME
+;src<dst
+!cpu 6502
+!to "aplib",plain
+*=$d000
+
+;unpacker variables, no need to change these
+src  = $0
+dst  = $2
+ecx  = $4
+last = $6
+tmp  = $8
+
+        lda     #>pakoff
+        sta     src+1
+        lda     #<pakoff
+        sta     src
+        lda     #0
+        sta     dst+1
+        sta     dst
+        sta     last
+        sta     ecx+1
+        jsr     unpack
+        tay ;returns A=0
+-       lda     $d600, y
+        sta     $bf00, y
+        iny
+        bne     -
+        ldx     $2b
+        stx     $bfd6 ;set current slot in RWTS
+        stx     $bfe4 ;set previous slot in RWTS
+        ldx     #$16
+--      stx     src
+        txa
+        asl
+        bit     src
+        beq     +
+        ora     src
+        eor     #$ff
+        and     #$7e
+-       bcs     +
+        lsr
+        bne     -
+        tya
+        sta     $fa80, x ;regenerate tables
+        txa
+        ora     #$80
+        sta     $fa29, y ;regenerate tables
+        iny
++       inx
+        bpl     --
+        tax ;A=FF
+        txs ;clean stack
+        jmp     $dd84 ;DOS entrypoint
+
+unpack ;unpacker entrypoint
+
+literal
+        jsr     getput
+        ldy     #2
+
+nexttag
+        jsr     getbit
+        bcc     literal
+        jsr     getbit
+        bcc     codepair
+        jsr     getbit
+        bcs     onebyte
+        jsr     getsrc
+        lsr
+        beq     donedepacking
+        ldx     #0
+        stx     ecx
+        rol     ecx
+        stx     last+1
+        tax
+        bne     domatch_with_2inc
+
+getbit
+        asl     last
+        bne     .stillbitsleft
+        jsr     getsrc
+        asl
+        sta     last
+        inc     last
+
+.stillbitsleft
+
+donedepacking
+        rts
+
+onebyte
+        ldy     #1
+        sty     ecx
+        iny
+        lda     #0
+        sta     tmp+1
+        lda     #$10
+
+.getmorebits
+        pha
+        jsr     getbit
+        pla
+        rol
+        bcc     .getmorebits
+        bne     domatch
+        jsr     putdst
+
+linktag
+        bne     nexttag
+
+codepair
+        jsr     getgamma
+-       jsr     dececx
+        dey
+        bne     -
+        tay
+        ora     ecx+1
+        beq     +
+
+normalcodepair
+        dey
+        sty     last+1
+        jsr     getsrc
+        tax
+        !byte   $a9
++       iny
+        jsr     getgamma
+        cpy     #$7d
+        bcs     domatch_with_2inc
+        cpy     #5
+        bcs     domatch_with_inc
+        txa
+        bmi     domatch_new_lastpos
+        tya
+        bne     domatch_new_lastpos
+
+domatch_with_2inc
+        inc     ecx
+        bne     domatch_with_inc
+        inc     ecx+1
+
+domatch_with_inc
+        inc     ecx
+        bne     domatch_new_lastpos
+        inc     ecx+1
+
+domatch_new_lastpos
+
+domatch_lastpos
+        ldy     #1
+        lda     last+1
+        sta     tmp+1
+        txa
+
+domatch
+        sta     tmp
+        lda     src+1
+        pha
+        lda     src
+        pha
+        lda     dst
+        clc
+        adc     tmp
+        sta     src
+        lda     dst+1
+        adc     tmp+1
+        sta     src+1
+-       jsr     getput
+        jsr     dececx
+        ora     ecx+1
+        bne     -
+        pla
+        sta     src
+        pla
+        sta     src+1
+        bne     linktag
+
+getgamma
+        lda     #1
+        sta     ecx
+        sta     ecx+1
+        dec     ecx+1
+
+.getgammaloop
+        jsr     getbit
+        rol     ecx
+        rol     ecx+1
+        jsr     getbit
+        bcs     .getgammaloop
+        rts
+
+dececx
+        lda     ecx
+        bne     +
+        dec     ecx+1
++       dec     ecx
+        lda     ecx
+        rts
+
+getput
+        jsr     getsrc
+
+putdst
+        pha
+        lda     dst
+        bne     +
+        dec     dst+1
++       dec     dst
+        pla
+        sty     tmp
+        ldy     #0
+        sta     (dst), y
+        ldy     tmp
+        rts
+
+getsrc
+        lda     src
+        bne     +
+        dec     src+1
++       dec     src
+        sty     tmp
+        ldy     #0
+        lda     (src), y
+        ldy     tmp
+        rts
+
+!bin "d600-ffff.rev.pak.rev"
+pakoff
diff --git a/make.txt b/make.txt
new file mode 100644
index 0000000..614761d
--- /dev/null
+++ b/make.txt
@@ -0,0 +1,15 @@
+How to make your own version:
+
+Take a regular version of Diversi-DOS, and save the $BF00-BFFF and $D700-FFFF regions to disk.
+Make whatever changes you will to that image.
+Fill the following regions with zeroes in the $D700 region:
+ - the read buffer at $1DBC-1FFF;
+ - the translate tables at offsets $2329-2368 and $2396-23FF (the unpacker will regenerate them);
+ - the write buffer at $2500-2655
+Concatenate the two images, with the $BF00 region first (to create a file named "d600-ffff").
+Reverse the order of the bytes in the image (to create a file named "d600-ffff.rev").
+Compress the result with aPLib ("appack c d600-ffff.rev d600-ffff.rev.pak").
+Remove the $18 bytes header from the resulting file.  The file size must not exceed $1F00 bytes!
+Reverse the order of the bytes in the image (to create a file named "d600-ffff.rev.pak.rev").
+Build the unpacker code with ACME.  The compressed image will be linked automatically to the output file.
+Write the output file to disk, beginning with T00 S01.