2020-11-20 22:14:18 +00:00
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; unlzsa1-6309.s - H6309 backward decompressor for raw LZSA1 - 97 bytes
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2020-11-01 21:57:50 +00:00
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; compress with lzsa -f1 -r -b <original_file> <compressed_file>
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;
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; in: x = last byte of compressed data
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; y = last byte of decompression buffer
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; out: y = first byte of decompressed data
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;
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; Copyright (C) 2020 Emmanuel Marty, Doug Masten
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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_lzsa1
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leax 1,x
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2020-11-20 22:14:18 +00:00
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bra lz1token
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2020-11-01 21:57:50 +00:00
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lz1bigof ldd ,--x ; O set: load long 16-bit (negative, signed) offest
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lz1gotof negd ; reverse sign of offset in D
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leau d,y ; put backreference start address in U (dst+offset)
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ldd #$000f ; clear MSB match length and set mask for MMMM
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andb ,s+ ; isolate MMMM (embedded match length) in token
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addb #$03 ; add MIN_MATCH_SIZE
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cmpb #$12 ; MATCH_RUN_LEN?
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bne lz1gotln ; no, we have the full match length, go copy
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addb ,-x ; add extra match length byte + MIN_MATCH_SIZE + MATCH_RUN_LEN
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bcc lz1gotln ; if no overflow, we have the full length
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bne lz1midln
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ldd ,--x ; load 16-bit len in D (low part in B, high in A)
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bne lz1gotln ; check if we hit EOD (16-bit length = 0)
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2020-11-20 22:14:18 +00:00
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leay 1,y ; adjust pointer to first byte of decompressed data
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2020-11-01 21:57:50 +00:00
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rts ; done, bail
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lz1midln tfr b,a ; copy high part of len into A
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ldb ,-x ; grab low 8 bits of len in B
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lz1gotln tfr d,w ; set W with match length for TFM instruction
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tfm u-,y- ; copy match bytes
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lz1token ldb ,-x ; load next token into B: O|LLL|MMMM
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pshs b ; save it
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andb #$70 ; isolate LLL (embedded literals count) in B
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beq lz1nolt ; skip if no literals
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cmpb #$70 ; LITERALS_RUN_LEN?
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bne lz1declt ; if not, we have the complete count, go unshift
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ldb ,-x ; load extra literals count byte
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addb #$07 ; add LITERALS_RUN_LEN
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bcc lz1gotla ; if no overflow, we got the complete count, copy
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bne lz1midlt
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ldd ,--x ; load 16 bit count in D (low part in B, high in A)
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bra lz1gotlt ; we now have the complete count, go copy
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lz1midlt tfr b,a ; copy high part of literals count into A
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ldb ,-x ; load low 8 bits of literals count
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bra lz1gotlt ; we now have the complete count, go copy
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lz1declt lsrb ; shift literals count into place
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lsrb
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lsrb
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lsrb
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lz1gotla clra ; clear A (high part of literals count)
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lz1gotlt tfr d,w ; set W with literals count for TFM instruction
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leax -1,x ; tfm is post-decrement
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tfm x-,y- ; copy literal bytes
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leax 1,x
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lz1nolt ldb ,s ; get token again, don't pop it from the stack
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bmi lz1bigof ; test O bit (small or large offset)
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ldb ,-x ; load either 8-bit or LSB 16-bit offset (negative, signed)
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lda #$ff ; set high 8 bits
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bra lz1gotof
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