lzsa/asm/6809/unlzsa1b.s
Doug Masten ecb6bc5106 Tiny speed improvement to 6809 LZSA depackers
Same space used but improved match length code by 1 cycle for M6809. On H6309 the clock cycles are the same.
2020-07-03 01:29:02 -05:00

106 lines
4.2 KiB
ArmAsm

; unlzsa1b.s - 6809 backward decompression routine for raw LZSA1 - 113 bytes
; compress with lzsa -r -b <original_file> <compressed_file>
;
; 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.
decompress_lzsa1
leax 1,x
leay 1,y
bra lz1token
lz1bigof ldd ,--x ; O set: load long 16 bit (negative, signed) offset
lz1gotof nega ; reverse sign of offset in D
negb
sbca #0
leau d,y ; put backreference start address in U (dst+offset)
ldd #$000f ; clear MSB match length and set mask for MMMM
andb ,s+ ; isolate MMMM (embedded match length) in token
addb #$03 ; add MIN_MATCH_SIZE
cmpb #$12 ; MATCH_RUN_LEN?
bne lz1gotln ; no, we have the full match length, go copy
addb ,-x ; add extra match length byte + MIN_MATCH_SIZE + MATCH_RUN_LEN
bcc lz1gotln ; if no overflow, we have the full length
bne lz1midln
ldd ,--x ; load 16-bit len in D (low part in B, high in A)
bne lz1gotln ; check if we hit EOD (16-bit length = 0)
rts ; done, bail
lz1midln tfr b,a ; copy high part of len into A
ldb ,-x ; grab low 8 bits of len in B
lz1gotln pshs x ; save source compressed data pointer
tfr d,x ; copy match length to X
lz1cpymt lda ,-u ; copy matched byte
sta ,-y
leax -1,x ; decrement X
bne lz1cpymt ; loop until all matched bytes are copied
puls x ; restore source compressed data pointer
lz1token ldb ,-x ; load next token into B: O|LLL|MMMM
pshs b ; save it
andb #$70 ; isolate LLL (embedded literals count) in B
beq lz1nolt ; skip if no literals
cmpb #$70 ; LITERALS_RUN_LEN?
bne lz1declt ; if not, we have the complete count, go unshift
ldb ,-x ; load extra literals count byte
addb #$07 ; add LITERALS_RUN_LEN
bcc lz1gotla ; if no overflow, we got the complete count, copy
bne lz1midlt
ldd ,--x ; load 16 bit count in D (low part in B, high in A)
bra lz1gotlt ; we now have the complete count, go copy
lz1midlt tfr b,a ; copy high part of literals count into A
ldb ,-x ; load low 8 bits of literals count
bra lz1gotlt ; we now have the complete count, go copy
lz1declt lsrb ; shift literals count into place
lsrb
lsrb
lsrb
lz1gotla clra ; clear A (high part of literals count)
lz1gotlt leau ,x
tfr d,x ; transfer 16-bit count into X
lz1cpylt lda ,-u ; copy literal byte
sta ,-y
leax -1,x ; decrement X and update Z flag
bne lz1cpylt ; loop until all literal bytes are copied
leax ,u
lz1nolt ldb ,s ; get token again, don't pop it from the stack
bmi lz1bigof ; test O bit (small or large offset)
ldb ,-x ; O clear: load 8 bit (negative, signed) offset
lda #$ff ; set high 8 bits
bra lz1gotof