dos33fsprogs/mist/decompress_fast_v2.s

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2020-03-05 05:25:59 +00:00
; note -- modified by Vince Weaver to assemble with ca65
; in this case, A = page to decompress to
; getsrc_smc+1, getsrc_smc+2 is src location
2020-03-05 05:25:59 +00:00
; -----------------------------------------------------------------------------
; Decompress raw LZSA2 block.
; Create one with lzsa -r -f2 <original_file> <compressed_file>
;
; in:
; * LZSA_SRC_LO and LZSA_SRC_HI contain the compressed raw block address
; * LZSA_DST_LO and LZSA_DST_HI contain the destination buffer address
;
; out:
; * LZSA_DST_LO and LZSA_DST_HI contain the last decompressed byte address, +1
;
; -----------------------------------------------------------------------------
; Backward decompression is also supported, use lzsa -r -b -f2 <original_file> <compressed_file>
; To use it, also define BACKWARD_DECOMPRESS=1 before including this code!
;
; in:
; * LZSA_SRC_LO/LZSA_SRC_HI must contain the address of the last byte of compressed data
; * LZSA_DST_LO/LZSA_DST_HI must contain the address of the last byte of the destination buffer
;
; out:
; * LZSA_DST_LO/LZSA_DST_HI contain the last decompressed byte address, -1
;
; -----------------------------------------------------------------------------
;
; Copyright (C) 2019 Emmanuel Marty, Peter Ferrie
;
; 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.
; -----------------------------------------------------------------------------
;NIBCOUNT = $FC ; zero-page location for temp offset
decompress_lzsa2_fast:
sta LZSA_DST_HI
ldy #$00
sty LZSA_DST_LO
sty NIBCOUNT
decode_token:
jsr getsrc ; read token byte: XYZ|LL|MMM
pha ; preserve token on stack
and #$18 ; isolate literals count (LL)
beq no_literals ; skip if no literals to copy
cmp #$18 ; LITERALS_RUN_LEN_V2?
bcc prepare_copy_literals ; if less, count is directly embedded in token
jsr getnibble ; get extra literals length nibble
; add nibble to len from token
adc #$02 ; (LITERALS_RUN_LEN_V2) minus carry
cmp #$12 ; LITERALS_RUN_LEN_V2 + 15 ?
bcc prepare_copy_literals_direct ; if less, literals count is complete
jsr getsrc ; get extra byte of variable literals count
; the carry is always set by the CMP above
; GETSRC doesn't change it
sbc #$EE ; overflow?
jmp prepare_copy_literals_direct
prepare_copy_literals_large:
; handle 16 bits literals count
; literals count = directly these 16 bits
jsr getlargesrc ; grab low 8 bits in X, high 8 bits in A
tay ; put high 8 bits in Y
bcs prepare_copy_literals_high ; (*same as JMP PREPARE_COPY_LITERALS_HIGH but shorter)
prepare_copy_literals:
lsr ; shift literals count into place
lsr
lsr
prepare_copy_literals_direct:
tax
bcs prepare_copy_literals_large ; if so, literals count is large
prepare_copy_literals_high:
txa
beq copy_literals
iny
copy_literals:
jsr getput ; copy one byte of literals
dex
bne copy_literals
dey
bne copy_literals
no_literals:
pla ; retrieve token from stack
pha ; preserve token again
asl
bcs repmatch_or_large_offset ; 1YZ: rep-match or 13/16 bit offset
asl ; 0YZ: 5 or 9 bit offset
bcs offset_9_bit
; 00Z: 5 bit offset
ldx #$FF ; set offset bits 15-8 to 1
jsr getcombinedbits ; rotate Z bit into bit 0, read nibble for bits 4-1
ora #$E0 ; set bits 7-5 to 1
bne got_offset_lo ; go store low byte of match offset and prepare match
offset_9_bit: ; 01Z: 9 bit offset
;;asl ; shift Z (offset bit 8) in place
rol
rol
and #$01
eor #$FF ; set offset bits 15-9 to 1
bne got_offset_hi ; go store high byte, read low byte of match offset and prepare match
; (*same as JMP GOT_OFFSET_HI but shorter)
repmatch_or_large_offset:
asl ; 13 bit offset?
bcs repmatch_or_16bit ; handle rep-match or 16-bit offset if not
; 10Z: 13 bit offset
jsr getcombinedbits ; rotate Z bit into bit 8, read nibble for bits 12-9
adc #$DE ; set bits 15-13 to 1 and substract 2 (to substract 512)
bne got_offset_hi ; go store high byte, read low byte of match offset and prepare match
; (*same as JMP GOT_OFFSET_HI but shorter)
repmatch_or_16bit: ; rep-match or 16 bit offset
;;ASL ; XYZ=111?
bmi rep_match ; reuse previous offset if so (rep-match)
; 110: handle 16 bit offset
jsr getsrc ; grab high 8 bits
got_offset_hi:
tax
jsr getsrc ; grab low 8 bits
got_offset_lo:
sta OFFSLO ; store low byte of match offset
stx OFFSHI ; store high byte of match offset
rep_match:
.ifdef BACKWARD_DECOMPRESS
; Backward decompression - substract match offset
sec ; add dest + match offset
lda putdst+1 ; low 8 bits
OFFSLO = *+1
sbc #$AA
sta copy_match_loop+1 ; store back reference address
lda putdst+2
OFFSHI = *+1
sbc #$AA ; high 8 bits
sta copy_match_loop+2 ; store high 8 bits of address
sec
.else
; Forward decompression - add match offset
clc ; add dest + match offset
lda putdst+1 ; low 8 bits
OFFSLO = *+1
adc #$AA
sta copy_match_loop+1 ; store back reference address
OFFSHI = *+1
lda #$AA ; high 8 bits
adc putdst+2
sta copy_match_loop+2 ; store high 8 bits of address
.endif
pla ; retrieve token from stack again
and #$07 ; isolate match len (MMM)
adc #$01 ; add MIN_MATCH_SIZE_V2 and carry
cmp #$09 ; MIN_MATCH_SIZE_V2 + MATCH_RUN_LEN_V2?
bcc prepare_copy_match ; if less, length is directly embedded in token
jsr getnibble ; get extra match length nibble
; add nibble to len from token
adc #$08 ; (MIN_MATCH_SIZE_V2 + MATCH_RUN_LEN_V2) minus carry
cmp #$18 ; MIN_MATCH_SIZE_V2 + MATCH_RUN_LEN_V2 + 15?
bcc prepare_copy_match ; if less, match length is complete
jsr getsrc ; get extra byte of variable match length
; the carry is always set by the CMP above
; GETSRC doesn't change it
sbc #$E8 ; overflow?
prepare_copy_match:
tax
bcc prepare_copy_match_y ; if not, the match length is complete
beq decompression_done ; if EOD code, bail
; Handle 16 bits match length
jsr getlargesrc ; grab low 8 bits in X, high 8 bits in A
tay ; put high 8 bits in Y
prepare_copy_match_y:
txa
beq copy_match_loop
iny
copy_match_loop:
lda $AAAA ; get one byte of backreference
jsr putdst ; copy to destination
.ifdef BACKWARD_DECOMPRESS
; Backward decompression -- put backreference bytes backward
lda copy_match_loop+1
beq getmatch_adj_hi
getmatch_done:
dec copy_match_loop+1
.else
; Forward decompression -- put backreference bytes forward
inc copy_match_loop+1
beq getmatch_adj_hi
getmatch_done:
.endif
dex
bne copy_match_loop
dey
bne copy_match_loop
jmp decode_token
.ifdef BACKWARD_DECOMPRESS
getmatch_adj_hi:
dec copy_match_loop+2
jmp getmatch_done
.else
getmatch_adj_hi:
inc copy_match_loop+2
jmp getmatch_done
.endif
getcombinedbits:
eor #$80
asl
php
jsr getnibble ; get nibble into bits 0-3 (for offset bits 1-4)
plp ; merge Z bit as the carry bit (for offset bit 0)
combinedbitz:
rol ; nibble -> bits 1-4; carry(!Z bit) -> bit 0 ; carry cleared
decompression_done:
rts
getnibble:
NIBBLES = *+1
lda #$AA
lsr NIBCOUNT
bcc need_nibbles
and #$0F ; isolate low 4 bits of nibble
rts
need_nibbles:
inc NIBCOUNT
jsr getsrc ; get 2 nibbles
sta NIBBLES
lsr
lsr
lsr
lsr
sec
rts
.ifdef BACKWARD_DECOMPRESS
; Backward decompression -- get and put bytes backward
getput:
jsr getsrc
putdst:
LZSA_DST_LO = *+1
LZSA_DST_HI = *+2
sta $AAAA
lda putdst+1
beq putdst_adj_hi
dec putdst+1
rts
putdst_adj_hi:
dec putdst+2
dec putdst+1
rts
getlargesrc:
jsr getsrc ; grab low 8 bits
tax ; move to X
; fall through grab high 8 bits
getsrc:
LZSA_SRC_LO = *+1
LZSA_SRC_HI = *+2
lda $AAAA
pha
lda getsrc+1
beq getsrc_adj_hi
dec getsrc+1
pla
rts
getsrc_adj_hi:
dec getsrc+2
dec getsrc+1
pla
rts
.else
; Forward decompression -- get and put bytes forward
getput:
jsr getsrc
putdst:
LZSA_DST_LO = *+1
LZSA_DST_HI = *+2
sta $AAAA
inc putdst+1
beq putdst_adj_hi
rts
putdst_adj_hi:
inc putdst+2
rts
getlargesrc:
jsr getsrc ; grab low 8 bits
tax ; move to X
; fall through grab high 8 bits
getsrc:
getsrc_smc:
2020-03-05 05:25:59 +00:00
LZSA_SRC_LO = *+1
LZSA_SRC_HI = *+2
lda $AAAA
inc getsrc+1
beq getsrc_adj_hi
rts
getsrc_adj_hi:
inc getsrc+2
rts
.endif