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; unaplib_6309_b.s - aPLib backward decompressor for H6309 - 139 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.
; Original M6809 version written by Emmanuel Marty with Hitachi 6309 enhancements
; added by Doug Masten.
;
; Main advantage of H6309 CPU is the "TFM" instruction which can copy one
; byte of memory in 3 clock cycles vs a traditional copy loop that takes
; 20 clock cycles.
; Options:
; APLIB_VAR
; Define variable to point to a DP memory location for a memory space
; and speed optimization.
; ex. APLIB_VAR equ <memory location>
;
; APLIB_LONG_OFFSET_DISABLE
; Defined variable to disable long offsets >= 32000 for a speed and space
; optimization. Only enable this if you know what you are doing.
; ex. APLIB_LONG_OFFSET_DISABLE equ 1
; define options
ifdef APLIB_VAR
apbitbuf equ APLIB_VAR ; bit queue (use DP memory for mem & space optimization)
else
apbitbuf fcb 0 ; bit queue (DEFAULT - use extended memory)
endc
apl_decompress
lda #$80 ; initialize empty bit queue
sta apbitbuf ; plus bit to roll into carry
leau 1,x
leay 1,y
apcplit ldb ,-u ; copy literal byte
apwtlit stb ,-y
ldb #3 ; 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
bsr apgamma2 ; 10: read gamma2-coded high offset bits
clra
subr d,w ; 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 f,a ; transfer high offset bits to A
ldb ,-u ; read low offset byte in B
tfr d,x ; save match offset
bsr apgamma2 ; read match length
ifndef APLIB_LONG_OFFSET_DISABLE
cmpx #$7D00 ; offset >= 32000 ?
bge apincby2 ; if so, increase match len by 2
endc
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 incw
apincby1 incw
apgotlen tfr y,d ; transfer dst to D
addr x,d ; put backreference start address in D (dst + offset)
decd
leay -1,y
tfm d-,y- ; copy matched bytes
leay 1,y
ldb #2 ; clear 'follows literal' flag
bra aptoken
apgamma2 ldw #1 ; init to 1 so it gets shifted to 2 below
loop@ bsr apgetbit ; read data bit
rolw ; shift into W
bsr apgetbit ; read continuation bit
bcs loop@ ; loop until a zero continuation bit is read
rts
apdibits bsr apgetbit ; read bit
rolb ; push into B
apgetbit lsl apbitbuf ; shift bit queue, and high bit into carry
bne aprts ; queue not empty, bits remain
lda ,-u ; read 8 new bits
rola ; shift bit queue, and high bit into carry
sta apbitbuf ; save bit queue
aprts rts
apshort clrb
bsr apdibits ; read 2 offset bits
rolb
bsr apdibits ; read 4 offset bits
rolb
beq apwtlit ; if zero, go write it
decb ; we load below without predecrement, adjust here
ldb b,y ; load backreferenced byte from dst+offset
bra apwtlit ; go write it
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 aprts ; check for EOD and exit if so
clra ; clear high bits in A
lsrb ; shift offset in place, shift length bit into carry
tfr d,x ; save match offset
ldb #1 ; len in B will be 2*1+carry:
rolb ; shift length, and carry into B
tfr d,w
bra apgotlen ; go copy match
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