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Add 6809 depacker for LZSA2
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Emmanuel Marty
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167
asm/6809/unlzsa2.s
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167
asm/6809/unlzsa2.s
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; unlzsa2.s - 6809 decompression routine for raw LZSA2 - 198 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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; y = start of decompression buffer
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; out: y = end of decompression buffer + 1
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;
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; Copyright (C) 2020 Emmanuel Marty
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;
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; This software is provided 'as-is', without any express or implied
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; warranty. In no event will the authors be held liable for any damages
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; arising from the use of this software.
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;
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; Permission is granted to anyone to use this software for any purpose,
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; including commercial applications, and to alter it and redistribute it
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; freely, subject to the following restrictions:
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;
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; 1. The origin of this software must not be misrepresented; you must not
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; claim that you wrote the original software. If you use this software
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; in a product, an acknowledgment in the product documentation would be
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; appreciated but is not required.
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; 2. Altered source versions must be plainly marked as such, and must not be
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; misrepresented as being the original software.
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; 3. This notice may not be removed or altered from any source distribution.
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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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lz2token ldb ,x+ ; load next token into B: XYZ|LL|MMM
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pshs b ; save it
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lda #$00 ; clear A (high part of literals count)
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andb #$18 ; isolate LLL (embedded literals count) in B
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beq lz2nolt ; skip if no literals
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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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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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ldb ,x+ ; load extra literals count byte
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addb #$12 ; add LITERALS_RUN_LEN + 15
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bcc lz2gotlt ; if no overflow, we got the complete count, copy
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ldb ,x+ ; load low 8 bits of little-endian literals count
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lda ,x+ ; load high 8 bits of literal count
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bra lz2gotlt ; we now have the complete count, go copy
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lz2declt lsrb ; shift literals count into place
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lsrb
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lsrb
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lz2gotlt tfr x,u
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tfr d,x ; transfer 16-bit count into X
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lz2cpylt lda ,u+ ; copy literal byte
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sta ,y+
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leax -1,x ; decrement X and update Z flag
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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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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 #$aa ; merge offset bit 0 from A
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lda #$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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rola ; shift Z flag from carry into bit 0 of A
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eora #$ff ; set bits 9-15 of offset, reverse bit 8
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ldb ,x+ ; load low 8 bits of (negative, signed) offset
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bra lz2gotof
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lz2nibbl ldb #$aa
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lsr lz2nibct ; nibble ready?
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bcs lz2gotnb
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inc lz2nibct ; 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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lsrb ; shift 4 high bits of nibble down
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lsrb
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lsrb
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lsrb
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lz2gotnb andb #$0f ; only keep low 4 bits
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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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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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suba #$02 ; substract 512 from offset
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ldb ,x+ ; load low 8 bits of (negative, signed) offset
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bra lz2gotof
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lz2rep16 bmi lz2repof ; if token's Z flag bit is set, rep match
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ldd ,x++ ; load high then low 8 bits of offset
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lz2gotof std lz2repof+1 ; store match offset
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lz2repof ldd #$aaaa ; load match offset
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leau d,y ; put backreference start address in U (dst+offset)
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puls b ; restore token
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lda #$00 ; clear A (high part of match length)
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andb #$07 ; isolate MMM (embedded match length)
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addb #$02 ; add MIN_MATCH_SIZE_V2
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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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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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ldb ,x+ ; load extra length byte
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addb #$18 ; add MIN_MATCH_SIZE_V2 + MATCH_RUN_LEN_V2 + 15
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bcc lz2gotln ; if no overflow, we have the full length
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beq lz2done ; detect EOD code
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ldb ,x+ ; load 16-bit len in D (low part in B, high in A)
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lda ,x+ ; (little endian)
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lz2gotln pshs x ; save source compressed data pointer
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tfr d,x ; copy match length to X
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lz2cpymt lda ,u+ ; copy matched byte
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sta ,y+
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leax -1,x ; decrement X
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bne lz2cpymt ; loop until all matched bytes are copied
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puls x ; restore source compressed data pointer
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jmp lz2token ; go decode next token
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lz2nibct rmb 1 ; nibble ready flag
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