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-5 bytes and faster 6809 LZSA2 depacker

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Emmanuel Marty 2020-06-19 12:50:10 +02:00 committed by GitHub
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1 changed files with 26 additions and 29 deletions
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55
asm/6809/unlzsa2.s
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@ -1,4 +1,4 @@
; unlzsa2.s - 6809 decompression routine for raw LZSA2 - 197 bytes
; unlzsa2.s - 6809 decompression routine for raw LZSA2 - 192 bytes
; compress with lzsa -f2 -r <original_file> <compressed_file>
;
; in: x = start of compressed data
@ -25,7 +25,7 @@
decompress_lzsa2
ldb #$00
stb lz2nibct ; clear nibble available flag
stb lz2nibct,pcr ; clear nibble available flag
lz2token ldb ,x+ ; load next token into B: XYZ|LL|MMM
pshs b ; save it
@ -36,7 +36,7 @@ lz2token ldb ,x+ ; load next token into B: XYZ|LL|MMM
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
bsr lz2nibl ; 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
@ -61,41 +61,41 @@ lz2cpylt lda ,u+ ; copy literal byte
bne lz2cpylt ; loop until all literal bytes are copied
tfr u,x
lz2nolt puls b ; restore token
pshs b ; save it again
lz2nolt ldb ,s ; get token again, don't pop it from the stack
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 #$aa ; merge offset bit 0 from A
tfr cc,a ; preserve cpu flags (to preserve carry)
bsr lz2nibl ; get offset nibble in B
tfr a,cc ; restore cpu flags
rolb ; shift Z flag from carry into bit 0 of B
eorb #$e1 ; set bits 5-7 of offset, reverse bit 0
lda #$ff ; set bits 8-15 of offset
bra lz2gotof
lz2offs9 lslb ; push token's Z flag bit into carry
lz2offs9 lda #$00 ; clear A (to prepare for high 8 bits of offset)
lslb ; push token's Z flag bit into carry
rola ; shift Z flag from carry into bit 0 of A
coma ; set bits 9-15 of offset, reverse bit 8
ldb ,x+ ; load low 8 bits of (negative, signed) offset
bra lz2gotof
lz2nibbl ldb #$aa
lsr lz2nibct ; nibble ready?
lz2nibct rmb 1 ; nibble ready flag
lz2nibl ldb #$aa
lsr lz2nibct,pcr ; nibble ready?
bcs lz2gotnb
inc lz2nibct ; flag nibble as ready for next time
inc lz2nibct,pcr ; flag nibble as ready for next time
ldb ,x+ ; load two nibbles
stb lz2nibbl+1 ; store nibble for next time (low 4 bits)
stb lz2nibl+1,pcr ; store nibble for next time (low 4 bits)
lsrb ; shift 4 high bits of nibble down
lsrb
@ -108,15 +108,14 @@ 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
tfr cc,a ; preserve cpu flags (to preserve carry)
bsr lz2nibl ; get offset nibble in B
tfr a,cc ; restore cpu flags
bsr lz2nibbl ; get offset nibble in B
lslb ; nibble represents offset bits 9..12
stb lz2val13+1
lz2val13 ora #$aa ; merge offset bits 9..12 from B
rolb ; shift Z flag from carry into bit 0 of B
eorb #$e1 ; set bits 13-15 of offset, reverse bit 8
tfr b,a ; copy bits 8-15 of offset into A
suba #$02 ; substract 512 from offset
ldb ,x+ ; load low 8 bits of (negative, signed) offset
@ -126,7 +125,7 @@ lz2rep16 bmi lz2repof ; if token's Z flag bit is set, rep match
ldd ,x++ ; load high then low 8 bits of offset
lz2gotof std lz2repof+1 ; store match offset
lz2gotof std lz2repof+1,pcr ; store match offset
lz2repof ldd #$aaaa ; load match offset
leau d,y ; put backreference start address in U (dst+offset)
@ -139,7 +138,7 @@ lz2repof ldd #$aaaa ; load match offset
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
bsr lz2nibl ; 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
@ -163,5 +162,3 @@ lz2cpymt lda ,u+ ; copy matched byte
puls x ; restore source compressed data pointer
lbra lz2token ; go decode next token
lz2nibct rmb 1 ; nibble ready flag