mirror of
https://github.com/emmanuel-marty/lzsa.git
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104 lines
4.2 KiB
NASM
Executable File
104 lines
4.2 KiB
NASM
Executable File
;
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; Speed-optimized LZSA decompressor by spke (v.1 03-05/04/2019, 122 bytes)
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;
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; The data must be comressed 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 -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 DecompressLZSA
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;
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; Of course, LZSA 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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; 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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@DecompressLZSA:
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ld b,0 : jr ReadToken
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MoreLiterals: ; there are three possible situations here
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; 1) a byte 0..253 is added to LLL and that is it or
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; 2) a byte 254 is followed by another byte to add or
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; 3) a byte 255 is followed by a word to be used
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ld a,7 : add (hl) : inc hl : jp nc,CopyLiterals
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.Overflow ; we get here if the literals length byte plus 7 is greater than 255
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inc b : cp 5 : jr c,CopyLiterals : jr nz,.Code255 ; 5 is 7+254 modulo 256
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.Code254 add (hl) : inc hl : jr nc,CopyLiterals : inc b : jr CopyLiterals
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.Code255 ld c,(hl) : inc hl : ld b,(hl) : inc hl : jr CopyLiterals.UseC
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; placed here this saves a JP per iteration
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CopyMatchNC scf ; flag C for SBC HL,DE below must be set!!!
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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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sbc hl,de : pop de ; BC = len, DE = dest, HL = dest-offset, SP->[src]
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ldir : pop hl ; BC = 0, DE = dest, HL = src
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ReadToken: ; first a byte token "O|LLL|MMMM" is read from the stream,
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; where LLL is the number of literals and MMMM is
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; a length of the match that follows after the literals
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ld a,(hl) : exa : ld a,(hl) : inc hl ; token is read twice to be re-used later
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and #70 : jr z,NoLiterals
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cp #70 : jr z,MoreLiterals ; LLL=7 means 7+ literals...
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rrca : rrca : rrca : rrca ; LLL<7 means 0..6 literals...
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CopyLiterals: ld c,a
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.UseC ldir
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NoLiterals: ; next we read the first byte of the offset
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push de : ld e,(hl) : inc hl
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; the top bit of token is set if the offset contains two bytes
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exa : and #8F : jp m,LongOffset
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ShortOffset: ld d,b ; we keep B=0 for situations like this
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; short matches have length 0+3..14+3
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ReadMatchLen: add 3 : cp 15+3 : jp c,CopyMatch
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; MMMM=15 indicates a multi-byte number of literals
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; there are three possible situations here
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; 1) a byte 0..253 is added to MMMM and that is it or
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; 2) a byte 254 is followed by another byte to add or
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; 3) a byte 255 is followed by a word to be used
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LongerMatch: add (hl) : inc hl : jp nc,CopyMatchNC
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.Overflow ; we get here if the match length byte plus 15+3 is greater than 255
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inc b : cp 16 : jr c,CopyMatch : jr nz,.Code255 ; 16 is 15+3+254 modulo 256
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.Code254 add (hl) : inc hl : jr nc,CopyMatchNC : inc b : jr CopyMatch
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.Code255 ld c,(hl) : inc hl : ld b,(hl) : inc hl
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; two-byte match length that is equal to zero is the marker for End-of-Data (EOD)
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.CheckEOD ld a,b : or c : jr nz,CopyMatch.UseC
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pop de : ret
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LongOffset: ; read second byte of the offset
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ld d,(hl) : inc hl
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add -128+3 : cp 15+3 : jp c,CopyMatch
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add (hl) : inc hl : jp nc,CopyMatchNC
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jr LongerMatch.Overflow
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