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Add 6502 decompressor
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emmanuel-marty
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207
asm/6502/decompress.asm
Executable file
207
asm/6502/decompress.asm
Executable file
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; -----------------------------------------------------------------------------
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; Decompress raw LZSA block. Create one with lzsa -r <original_file> <compressed_file>
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;
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; in:
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; * LZSA_SRC_LO and LZSA_SRC_HI contain the compressed raw block address
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; * LZSA_DST_LO and LZSA_DST_HI contain the destination buffer address
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;
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; out:
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; * LZSA_DST_LO and LZSA_DST_HI contain the last decompressed byte address, +1
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; -----------------------------------------------------------------------------
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;
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; Copyright (C) 2019 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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; -----------------------------------------------------------------------------
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OFFSLO = $43 ; zero-page location for temp offset
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OFFSHI = $44
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DECOMPRESS_LZSA
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LDY #$00
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DECODE_TOKEN
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JSR GETSRC ; read token byte: O|LLL|MMMM
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PHA ; preserve token on stack
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AND #$70 ; isolate literals count
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BEQ NO_LITERALS ; skip if no literals to copy
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CMP #$70 ; LITERALS_RUN_LEN?
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BNE EMBEDDED_LITERALS ; if not, count is directly embedded in token
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JSR GETSRC ; get extra byte of variable literals count
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CMP #$FF ; FF <low 8 bits> <high 8 bits>?
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BEQ LARGE_VARLEN_LITERALS ; yes, go grab it
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JSR GETSINGLEVARLENSRC ; handle single extra byte of variable literals count
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CLC ; add extra byte to len from token
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ADC #$07 ; (LITERALS_RUN_LEN)
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BCC PREPARE_COPY_LITERALS
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INY
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JMP PREPARE_COPY_LITERALS
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LARGE_VARLEN_LITERALS ; FF <low 8 bits> <high 8 bits>
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; literals count = directly these 16 bits
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JSR GETLARGESRC ; grab low 8 bits in X, high 8 bits in A
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TAY ; put high 8 bits in Y
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JMP PREPARE_COPY_LITERALS_HIGH
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EMBEDDED_LITERALS
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LSR A ; shift literals count into place
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LSR A
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LSR A
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LSR A
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PREPARE_COPY_LITERALS
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TAX
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PREPARE_COPY_LITERALS_HIGH
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INY
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COPY_LITERALS
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JSR GETPUT ; copy one byte of literals
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DEX
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BNE COPY_LITERALS
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DEY
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BNE COPY_LITERALS
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NO_LITERALS
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PLA ; retrieve token from stack
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PHA ; preserve token again
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AND #$80 ; isolate match offset mode (O)
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BNE GET_LONG_OFFSET ; $80: 16 bit offset
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JSR GETSRC ; get 8 bit offset from stream
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TAX ; store as low 8 bits of offset
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; Y (high 8 bits) is already set to 0 here
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JMP FIX_OFFSET ; go increase offset
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GET_LONG_OFFSET ; $00: 2-byte offset
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JSR GETLARGESRC ; grab low 8 bits in X, high 8 bits in A
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TAY ; put high 8 bits in Y
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FIX_OFFSET
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TXA ; add 1 to offset
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CLC
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ADC #$01
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BCC OFFSET_FIXED
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INY
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OFFSET_FIXED
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STA OFFSLO ; store final match offset
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STY OFFSHI
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LDY #$00 ; reset Y again
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PLA ; retrieve token from stack again
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AND #$0F ; isolate match len (MMMM)
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CMP #$0F ; MATCH_RUN_LEN?
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BNE PREPARE_COPY_MATCH ; if not, count is directly embedded in token
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JSR GETSRC ; get extra byte of variable match length
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CMP #$FF ; FF <low 8 bits> <high 8 bits>?
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BEQ LARGE_VARLEN_MATCHLEN ; yes, go grab it
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JSR GETSINGLEVARLENSRC ; handle single extra byte of variable match len
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CLC ; add extra byte to len from token
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ADC #$0F ; (MATCH_RUN_LEN)
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BCC PREPARE_COPY_MATCH
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INY
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JMP PREPARE_COPY_MATCH
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LARGE_VARLEN_MATCHLEN ; FF <low 8 bits> <high 8 bits>
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; match length = directly these 16 bits
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JSR GETLARGESRC ; grab low 8 bits in X, high 8 bits in A
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TAY ; put high 8 bits in Y
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; large match length with zero high byte?
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BEQ DECOMPRESSION_DONE ; if so, this is the EOD code, bail
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JMP PREPARE_COPY_MATCH_Y
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PREPARE_COPY_MATCH
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CLC ; add MIN_MATCH_SIZE to match length
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ADC #$03
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BCC MIN_MATCH_SIZE_ADDED
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INY
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MIN_MATCH_SIZE_ADDED
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TAX
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PREPARE_COPY_MATCH_Y
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INY
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COPY_MATCH
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SEC ; substract dest - match offset
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LDA PUTDST+1 ; low 8 bits
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SBC OFFSLO
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STA COPY_MATCH_LOOP+1 ; store back reference address
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LDA PUTDST+2 ; high 8 bits
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SBC OFFSHI
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STA COPY_MATCH_LOOP+2 ; store high 8 bits of address
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COPY_MATCH_LOOP
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LDA $AAAA ; get one byte of backreference
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INC COPY_MATCH_LOOP+1
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BNE GETMATCH_DONE
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INC COPY_MATCH_LOOP+2
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GETMATCH_DONE
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JSR PUTDST ; copy to destination
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DEX
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BNE COPY_MATCH_LOOP
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DEY
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BNE COPY_MATCH_LOOP
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JMP DECODE_TOKEN
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GETPUT
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JSR GETSRC
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PUTDST
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LZSA_DST_LO = *+1
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LZSA_DST_HI = *+2
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STA $AAAA
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INC PUTDST+1
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BNE PUTDST_DONE
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INC PUTDST+2
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PUTDST_DONE
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DECOMPRESSION_DONE
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RTS
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GETLARGESRC
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JSR GETSRC ; grab low 8 bits
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TAX ; move to X
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; fall through grab high 8 bits
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GETSRC
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LZSA_SRC_LO = *+1
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LZSA_SRC_HI = *+2
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LDA $AAAA
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INC GETSRC+1
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BNE GETSRC_DONE
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INC GETSRC+2
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GETSRC_DONE
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RTS
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GETSINGLEVARLENSRC
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CMP #$FE ; FE <extra 8 bits>?
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BNE SINGLE_VARLEN_ADDED ; no, just this byte
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JSR GETSRC ; get extra byte of variable literals count
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CLC ; add $FE to len from token
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ADC #$FE
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BCC SINGLE_VARLEN_ADDED
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INY
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SINGLE_VARLEN_ADDED
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RTS
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