lzsa/asm/6809/unlzsa2.s

168 lines
6.7 KiB
ArmAsm
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2020-06-18 15:48:08 +00:00
; unlzsa2.s - 6809 decompression routine for raw LZSA2 - 198 bytes
; compress with lzsa -f2 -r <original_file> <compressed_file>
;
; in: x = start of compressed data
; y = start of decompression buffer
; out: y = end of decompression buffer + 1
;
; 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_lzsa2
ldb #$00
stb lz2nibct ; clear nibble available flag
lz2token ldb ,x+ ; load next token into B: XYZ|LL|MMM
pshs b ; save it
lda #$00 ; clear A (high part of literals count)
andb #$18 ; isolate LLL (embedded literals count) in B
beq lz2nolt ; skip if no literals
cmpb #$18 ; LITERALS_RUN_LEN_V2?
bne lz2declt ; if not, we have the complete count, go unshift
bsr lz2nibbl ; get extra literals length nibble in B
addb #$03 ; add LITERALS_RUN_LEN_V2
cmpb #$12 ; LITERALS_RUN_LEN_V2 + 15 ?
bne lz2gotlt ; if not, we have the full literals count, go copy
ldb ,x+ ; load extra literals count byte
addb #$12 ; add LITERALS_RUN_LEN + 15
bcc lz2gotlt ; if no overflow, we got the complete count, copy
ldb ,x+ ; load low 8 bits of little-endian literals count
lda ,x+ ; load high 8 bits of literal count
bra lz2gotlt ; we now have the complete count, go copy
lz2declt lsrb ; shift literals count into place
lsrb
lsrb
lz2gotlt tfr x,u
tfr d,x ; transfer 16-bit count into X
lz2cpylt lda ,u+ ; copy literal byte
sta ,y+
leax -1,x ; decrement X and update Z flag
bne lz2cpylt ; loop until all literal bytes are copied
tfr u,x
lz2nolt puls b ; restore token
pshs b ; save it again
lslb ; push token's X flag bit into carry
bcs lz2replg ; if token's X bit is set, rep or large offset
lda #$00 ; clear A (to prepare for high 8 bits of offset)
lslb ; push token's Y flag bit into carry
bcs lz2offs9 ; if token's Y bit is set, 9 bits offset
lslb ; push token's Z flag bit into carry
rola ; shift Z flag from carry into bit 0 of A
eora #$e1 ; set bits 5-7 of offset, reverse bit 0
sta lz2val5+1
bsr lz2nibbl ; get offset nibble in B
lslb ; nibble represents offset bits 1..4
lz2val5 orb #$aa ; merge offset bit 0 from A
lda #$ff ; set bits 8-15 of offset
bra lz2gotof
lz2offs9 lslb ; push token's Z flag bit into carry
rola ; shift Z flag from carry into bit 0 of A
eora #$ff ; set bits 9-15 of offset, reverse bit 8
ldb ,x+ ; load low 8 bits of (negative, signed) offset
bra lz2gotof
lz2nibbl ldb #$aa
lsr lz2nibct ; nibble ready?
bcs lz2gotnb
inc lz2nibct ; flag nibble as ready for next time
ldb ,x+ ; load two nibbles
stb lz2nibbl+1 ; store nibble for next time (low 4 bits)
lsrb ; shift 4 high bits of nibble down
lsrb
lsrb
lsrb
lz2gotnb andb #$0f ; only keep low 4 bits
lz2done rts
lz2replg lslb ; push token's Y flag bit into carry
bcs lz2rep16 ; if token's Y bit is set, rep or 16 bit offset
lda #$00 ; clear A
lslb ; push token's Z flag bit into carry
rola ; shift Z flag from carry into bit 0 of A
eora #$e1 ; set bits 13-15 of offset, reverse bit 8
bsr lz2nibbl ; get offset nibble in B
lslb ; nibble represents offset bits 9..12
stb lz2val13+1
lz2val13 ora #$aa ; merge offset bits 9..12 from B
suba #$02 ; substract 512 from offset
ldb ,x+ ; load low 8 bits of (negative, signed) offset
bra lz2gotof
lz2rep16 bmi lz2repof ; if token's Z flag bit is set, rep match
ldd ,x++ ; load high then low 8 bits of offset
lz2gotof std lz2repof+1 ; store match offset
lz2repof ldd #$aaaa ; load match offset
leau d,y ; put backreference start address in U (dst+offset)
puls b ; restore token
lda #$00 ; clear A (high part of match length)
andb #$07 ; isolate MMM (embedded match length)
addb #$02 ; add MIN_MATCH_SIZE_V2
cmpb #$09 ; MIN_MATCH_SIZE_V2 + MATCH_RUN_LEN_V2?
bne lz2gotln ; no, we have the full match length, go copy
bsr lz2nibbl ; get offset nibble in B
addb #$09 ; add MIN_MATCH_SIZE_V2 + MATCH_RUN_LEN_V2
cmpb #$18 ; MIN_MATCH_SIZE_V2 + MATCH_RUN_LEN_V2 + 15?
bne lz2gotln ; if not, we have the full match length, go copy
ldb ,x+ ; load extra length byte
addb #$18 ; add MIN_MATCH_SIZE_V2 + MATCH_RUN_LEN_V2 + 15
bcc lz2gotln ; if no overflow, we have the full length
beq lz2done ; detect EOD code
ldb ,x+ ; load 16-bit len in D (low part in B, high in A)
lda ,x+ ; (little endian)
lz2gotln pshs x ; save source compressed data pointer
tfr d,x ; copy match length to X
lz2cpymt lda ,u+ ; copy matched byte
sta ,y+
leax -1,x ; decrement X
bne lz2cpymt ; loop until all matched bytes are copied
puls x ; restore source compressed data pointer
jmp lz2token ; go decode next token
lz2nibct rmb 1 ; nibble ready flag