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-5 bytes and faster 6809 LZSA2 depacker
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Emmanuel Marty
GitHub
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c3b111cea6
commit
f80706ff7e
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@ -1,4 +1,4 @@
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; unlzsa2.s - 6809 decompression routine for raw LZSA2 - 197 bytes
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; unlzsa2.s - 6809 decompression routine for raw LZSA2 - 192 bytes
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; compress with lzsa -f2 -r <original_file> <compressed_file>
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;
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; in: x = start of compressed data
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@ -25,7 +25,7 @@
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decompress_lzsa2
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ldb #$00
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stb lz2nibct ; clear nibble available flag
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stb lz2nibct,pcr ; clear nibble available flag
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lz2token ldb ,x+ ; load next token into B: XYZ|LL|MMM
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pshs b ; save it
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@ -36,7 +36,7 @@ lz2token ldb ,x+ ; load next token into B: XYZ|LL|MMM
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cmpb #$18 ; LITERALS_RUN_LEN_V2?
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bne lz2declt ; if not, we have the complete count, go unshift
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bsr lz2nibbl ; get extra literals length nibble in B
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bsr lz2nibl ; get extra literals length nibble in B
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addb #$03 ; add LITERALS_RUN_LEN_V2
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cmpb #$12 ; LITERALS_RUN_LEN_V2 + 15 ?
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bne lz2gotlt ; if not, we have the full literals count, go copy
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@ -61,41 +61,41 @@ lz2cpylt lda ,u+ ; copy literal byte
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bne lz2cpylt ; loop until all literal bytes are copied
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tfr u,x
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lz2nolt puls b ; restore token
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pshs b ; save it again
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lz2nolt ldb ,s ; get token again, don't pop it from the stack
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lslb ; push token's X flag bit into carry
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bcs lz2replg ; if token's X bit is set, rep or large offset
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lda #$00 ; clear A (to prepare for high 8 bits of offset)
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lslb ; push token's Y flag bit into carry
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bcs lz2offs9 ; if token's Y bit is set, 9 bits offset
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lslb ; push token's Z flag bit into carry
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rola ; shift Z flag from carry into bit 0 of A
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eora #$e1 ; set bits 5-7 of offset, reverse bit 0
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sta lz2val5+1
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bsr lz2nibbl ; get offset nibble in B
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lslb ; nibble represents offset bits 1..4
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lz2val5 orb #$aa ; merge offset bit 0 from A
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tfr cc,a ; preserve cpu flags (to preserve carry)
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bsr lz2nibl ; get offset nibble in B
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tfr a,cc ; restore cpu flags
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rolb ; shift Z flag from carry into bit 0 of B
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eorb #$e1 ; set bits 5-7 of offset, reverse bit 0
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lda #$ff ; set bits 8-15 of offset
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bra lz2gotof
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lz2offs9 lslb ; push token's Z flag bit into carry
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lz2offs9 lda #$00 ; clear A (to prepare for high 8 bits of offset)
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lslb ; push token's Z flag bit into carry
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rola ; shift Z flag from carry into bit 0 of A
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coma ; set bits 9-15 of offset, reverse bit 8
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ldb ,x+ ; load low 8 bits of (negative, signed) offset
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bra lz2gotof
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lz2nibbl ldb #$aa
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lsr lz2nibct ; nibble ready?
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lz2nibct rmb 1 ; nibble ready flag
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lz2nibl ldb #$aa
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lsr lz2nibct,pcr ; nibble ready?
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bcs lz2gotnb
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inc lz2nibct ; flag nibble as ready for next time
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inc lz2nibct,pcr ; flag nibble as ready for next time
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ldb ,x+ ; load two nibbles
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stb lz2nibbl+1 ; store nibble for next time (low 4 bits)
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stb lz2nibl+1,pcr ; store nibble for next time (low 4 bits)
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lsrb ; shift 4 high bits of nibble down
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lsrb
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@ -108,15 +108,14 @@ lz2done rts
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lz2replg lslb ; push token's Y flag bit into carry
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bcs lz2rep16 ; if token's Y bit is set, rep or 16 bit offset
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lda #$00 ; clear A
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lslb ; push token's Z flag bit into carry
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rola ; shift Z flag from carry into bit 0 of A
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eora #$e1 ; set bits 13-15 of offset, reverse bit 8
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tfr cc,a ; preserve cpu flags (to preserve carry)
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bsr lz2nibl ; get offset nibble in B
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tfr a,cc ; restore cpu flags
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bsr lz2nibbl ; get offset nibble in B
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lslb ; nibble represents offset bits 9..12
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stb lz2val13+1
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lz2val13 ora #$aa ; merge offset bits 9..12 from B
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rolb ; shift Z flag from carry into bit 0 of B
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eorb #$e1 ; set bits 13-15 of offset, reverse bit 8
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tfr b,a ; copy bits 8-15 of offset into A
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suba #$02 ; substract 512 from offset
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ldb ,x+ ; load low 8 bits of (negative, signed) offset
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@ -126,7 +125,7 @@ lz2rep16 bmi lz2repof ; if token's Z flag bit is set, rep match
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ldd ,x++ ; load high then low 8 bits of offset
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lz2gotof std lz2repof+1 ; store match offset
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lz2gotof std lz2repof+1,pcr ; store match offset
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lz2repof ldd #$aaaa ; load match offset
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leau d,y ; put backreference start address in U (dst+offset)
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@ -139,7 +138,7 @@ lz2repof ldd #$aaaa ; load match offset
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cmpb #$09 ; MIN_MATCH_SIZE_V2 + MATCH_RUN_LEN_V2?
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bne lz2gotln ; no, we have the full match length, go copy
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bsr lz2nibbl ; get offset nibble in B
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bsr lz2nibl ; get offset nibble in B
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addb #$09 ; add MIN_MATCH_SIZE_V2 + MATCH_RUN_LEN_V2
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cmpb #$18 ; MIN_MATCH_SIZE_V2 + MATCH_RUN_LEN_V2 + 15?
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bne lz2gotln ; if not, we have the full match length, go copy
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@ -163,5 +162,3 @@ lz2cpymt lda ,u+ ; copy matched byte
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puls x ; restore source compressed data pointer
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lbra lz2token ; go decode next token
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lz2nibct rmb 1 ; nibble ready flag
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