From 9bcf1e97960c0da7322a868efdbc07e2650716fe Mon Sep 17 00:00:00 2001
From: "Juan J. Martinez" <jjm@usebox.net>
Date: Sat, 9 Jan 2021 09:01:05 +0000
Subject: Extra libs: ap.lib

aPLib support with apultra.
---
 tools/apultra/asm/6809/unaplib_b.s | 122 +++++++++++++++++++++++++++++++++++++
 1 file changed, 122 insertions(+)
 create mode 100644 tools/apultra/asm/6809/unaplib_b.s

(limited to 'tools/apultra/asm/6809/unaplib_b.s')

diff --git a/tools/apultra/asm/6809/unaplib_b.s b/tools/apultra/asm/6809/unaplib_b.s
new file mode 100644
index 0000000..02f943c
--- /dev/null
+++ b/tools/apultra/asm/6809/unaplib_b.s
@@ -0,0 +1,122 @@
+;  unaplib_b.s - aPLib backward decompressor for 6809 - 154 bytes
+;
+;  in:  x = last byte of compressed data
+;       y = last byte of decompression buffer
+;  out: y = first byte of decompressed data
+;
+;  Copyright (C) 2020 Emmanuel Marty
+;
+;  This software is provided 'as-is', without any express or implied
+;  warranty.  In no event will the authors be held liable for any damages
+;  arising from the use of this software.
+;
+;  Permission is granted to anyone to use this software for any purpose,
+;  including commercial applications, and to alter it and redistribute it
+;  freely, subject to the following restrictions:
+;
+;  1. The origin of this software must not be misrepresented; you must not
+;     claim that you wrote the original software. If you use this software
+;     in a product, an acknowledgment in the product documentation would be
+;     appreciated but is not required.
+;  2. Altered source versions must be plainly marked as such, and must not be
+;     misrepresented as being the original software.
+;  3. This notice may not be removed or altered from any source distribution.
+
+apl_decompress
+         lda #$80          ; initialize empty bit queue
+         sta <apbitbuf,pcr ; plus bit to roll into carry
+         leau 1,x
+         leay 1,y
+
+apcplit  ldb ,-u           ; copy literal byte
+apwtlit  stb ,-y
+
+         lda #$03          ; set 'follows literal' flag
+
+aptoken  bsr apgetbit      ; read 'literal or match' bit
+         bcc apcplit       ; if 0: literal
+
+         bsr apgetbit      ; read '8+n bits or other type' bit
+         bcs apother       ; if 11x: other type of match
+
+         sta <aplwm+2,pcr  ; store 'follows literal' flag
+
+         bsr apgamma2      ; 10: read gamma2-coded high offset bits
+aplwm    subd #$0000       ; high offset bits == 2 when follows_literal == 3 ?
+         bcc apnorep       ; if not, not a rep-match
+
+         bsr apgamma2      ; read repmatch length
+         bra apgotlen      ; go copy large match
+
+apnorep  tfr b,a           ; transfer high offset bits to A
+         ldb ,-u           ; read low offset byte in B
+         std <aprepof+2,pcr ; store match offset
+         tfr d,x           ; transfer offset to X
+
+         bsr apgamma2      ; read match length
+
+         cmpx #$7D00       ; offset >= 32000 ?
+         bge apincby2      ; if so, increase match len by 2
+         cmpx #$0500       ; offset >= 1280 ?
+         bge apincby1      ; if so, increase match len by 1
+         cmpx #$80         ; offset < 128 ?
+         bge apgotlen      ; if so, increase match len by 2
+apincby2 addd #1
+apincby1 addd #1
+apgotlen pshs u            ; save source compressed data pointer
+         tfr d,x           ; copy match length to X
+
+aprepof  leau $aaaa,y      ; put backreference start address in U (dst+offset)
+
+apcpymt  lda ,-u           ; copy matched byte
+         sta ,-y
+         leax -1,x         ; decrement X
+         bne apcpymt       ; loop until all matched bytes are copied
+
+         puls u            ; restore source compressed data pointer
+
+         lda #$02          ; clear 'follows literal' flag
+         bra aptoken
+
+apdibits bsr apgetbit      ; read bit
+         rolb              ; push into B
+apgetbit lsl <apbitbuf,pcr ; shift bit queue, and high bit into carry
+         bne apdone        ; queue not empty, bits remain
+         pshs a            ; push reg A
+         lda ,-u           ; read 8 new bits
+         rola              ; shift bit queue, and high bit into carry
+         sta <apbitbuf,pcr ; save bit queue
+         puls a,pc         ; pop reg A and return
+
+apbitbuf fcb $00           ; bit queue
+
+apshort  clrb
+         bsr apdibits      ; read 2 offset bits
+         rolb
+         bsr apdibits      ; read 4 offset bits
+         rolb
+         beq apwtlit       ; go write a zero
+
+         decb              ; we load below without predecrement, adjust here
+         ldb b,y           ; load backreferenced byte from dst+offset
+         bra apwtlit       ; go write backreferenced byte
+
+apgamma2 ldd #$1           ; init to 1 so it gets shifted to 2 below
+apg2loop bsr apgetbit      ; read data bit
+         rolb              ; shift into D
+         rola
+         bsr apgetbit      ; read continuation bit
+         bcs apg2loop      ; loop until a zero continuation bit is read
+apdone   rts
+
+apother  bsr apgetbit      ; read '7+1 match or short literal' bit
+         bcs apshort       ; if 111: 4 bit offset for 1-byte copy
+
+         ldb ,-u           ; read low bits of offset + length bit in B
+         beq apdone        ; check for EOD
+         clra              ; clear high bits in A
+         lsrb              ; shift offset in place, shift length bit into carry
+         std <aprepof+2,pcr ; store match offset
+         ldb #$01          ; len in B will be 2*1+carry:
+         rolb              ; shift length, and carry into B
+         bra apgotlen      ; go copy match
-- 
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