mirror of
https://github.com/emmanuel-marty/lzsa.git
synced 2024-11-04 08:04:47 +00:00
168 lines
3.8 KiB
NASM
168 lines
3.8 KiB
NASM
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; Speed-optimized LZSA2 decompressor by spke (v.1 02-07/06/2019, 218 bytes)
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;
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; The data must be compressed using the command line compressor by Emmanuel Marty
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; The compression is done as follows:
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;
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; lzsa.exe -f2 -r <sourcefile> <outfile>
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;
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; where option -r asks for the generation of raw (frame-less) data.
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;
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; The decompression is done in the standard way:
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;
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; ld hl,CompressedData
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; ld de,WhereToDecompress
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; call DecompressLZSA2
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;
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; Of course, LZSA2 compression algorithm is (c) 2019 Emmanuel Marty,
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; see https://github.com/emmanuel-marty/lzsa for more information
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;
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; Drop me an email if you have any comments/ideas/suggestions: zxintrospec@gmail.com
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;
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@DecompressLZSA2:
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; A' stores next nibble as %1111.... or assumed to contain trash
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; B is assumed to be 0
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xor a : ld b,a : exa : jr ReadToken
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LongerMatch: exa : jp m,.noUpdate
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ld a,(hl) : or #F0 : exa
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ld a,(hl) : inc hl : or #0F
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rrca : rrca : rrca : rrca
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.noUpdate sub #F0-9 : cp 15+9 : jr c,CopyMatch
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;inc a : jr z,LongMatch : sub #F0-9+1 : jp CopyMatch
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LongMatch: ;ld a,24 :
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add (hl) : inc hl : jr nc,CopyMatch
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ld c,(hl) : inc hl
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ld b,(hl) : inc hl
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jr nz,CopyMatch.useC
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pop de : ret
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ManyLiterals: ld a,18 :
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add (hl) : inc hl : jr nc,CopyLiterals
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ld c,(hl) : inc hl
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ld a,b : ld b,(hl) : inc hl
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jr CopyLiterals.useBC
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MoreLiterals: ld b,(hl) : inc hl
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exa : jp m,.noUpdate
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ld a,(hl) : or #F0 : exa
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ld a,(hl) : inc hl : or #0F
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rrca : rrca : rrca : rrca
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.noUpdate ;sub #F0-3 : cp 15+3 : jr z,ManyLiterals
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inc a : jr z,ManyLiterals : sub #F0-3+1
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CopyLiterals: ld c,a
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.useC ld a,b : ld b,0
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.useBC ldir
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push de : or a : jp p,CASE0xx : jr CASE1xx
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; if "LL" of the byte token is equal to 0,
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; there are no literals to copy
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NoLiterals: xor (hl) : inc hl
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push de : jp m,CASE1xx
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; short (5 or 9 bit long) offsets
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CASE0xx ld d,#FF : cp %01000000 : jr c,CASE00x
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; "01x": the case of the 9-bit offset
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CASE01x: cp %01100000 : rl d
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ReadOffsetE: ld e,(hl) : inc hl
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SaveOffset: ld ixl,e : ld ixh,d
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MatchLen: inc a : and %00000111 : jr z,LongerMatch : inc a
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CopyMatch: ld c,a
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.useC ex (sp),hl : push hl ; BC = len, DE = offset, HL = dest, SP ->[dest,src]
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add hl,de : pop de ; BC = len, DE = dest, HL = dest-offset, SP->[src]
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ldir : pop hl
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; compressed data stream contains records
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; each record begins with the byte token "XYZ|LL|MMM"
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ReadToken: ld a,(hl) : and %00011000 : jr z,NoLiterals
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jp pe,MoreLiterals ; 00 has already been processed; this identifies the case of 11
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rrca : rrca : rrca
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ld c,a : ld a,(hl) : inc hl ; token is re-read for further processing
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ldir
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; the token and literals are followed by the offset
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push de : or a : jp p,CASE0xx
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CASE1xx cp %11000000 : jr nc,CASE11x
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; "10x": the case of the 5-bit offset
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CASE10x: ld c,a : xor a
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exa : jp m,.noUpdate
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ld a,(hl) : or #F0 : exa
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ld a,(hl) : inc hl : or #0F
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rrca : rrca : rrca : rrca
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.noUpdate ld d,a : ld a,c
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cp %10100000 : rl d
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dec d : dec d : jr ReadOffsetE
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; "00x": the case of the 5-bit offset
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CASE00x: ld c,a : xor a
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exa : jp m,.noUpdate
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ld a,(hl) : or #F0 : exa
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ld a,(hl) : inc hl : or #0F
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rrca : rrca : rrca : rrca
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.noUpdate ld e,a : ld a,c
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cp %00100000 : rl e : jp SaveOffset
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; two remaining cases
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CASE11x cp %11100000 : jr c,CASE110
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; "111": repeated offset
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CASE111: ld e,ixl : ld d,ixh : jr MatchLen
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; "110": 16-bit offset
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CASE110: ld d,(hl) : inc hl : jr ReadOffsetE
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;ReadNibble: ; 17 bytes, 44 t-state per nibble
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; exa : ret m ; 4+11 = 15t
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;UpdateNibble:
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; ld a,(hl) : or #F0 : exa
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; ld a,(hl) : inc hl : or #0F
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; rrca : rrca : rrca : rrca : ret ; 4+5 + 7+7+4+7+6+7+4+4+4+4+10 = 73t
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