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;
; Size-optimized LZSA decompressor by spke (v.1 23/04/2019, 69 bytes)
;
; The data must be compressed using the command line compressor by Emmanuel Marty
; The compression is done as follows:
;
; lzsa.exe -r <sourcefile> <outfile>
;
; where option -r asks for the generation of raw (frame-less) data.
;
; The decompression is done in the standard way:
;
; ld hl,CompressedData
; ld de,WhereToDecompress
; call DecompressLZSA
;
; Of course, LZSA compression algorithm is (c) 2019 Emmanuel Marty,
; see https://github.com/emmanuel-marty/lzsa for more information
;
; Drop me an email if you have any comments/ideas/suggestions: zxintrospec@gmail.com
;
; This software is provided 'as-is', without any express or implied
; warranty. In no event will the authors be held liable for any damages
; arising from the use of this software.
;
; Permission is granted to anyone to use this software for any purpose,
; including commercial applications, and to alter it and redistribute it
; freely, subject to the following restrictions:
;
; 1. The origin of this software must not be misrepresented; you must not
; claim that you wrote the original software. If you use this software
; in a product, an acknowledgment in the product documentation would be
; appreciated but is not required.
; 2. Altered source versions must be plainly marked as such, and must not be
; misrepresented as being the original software.
; 3. This notice may not be removed or altered from any source distribution.
;
@DecompressLZSA:
ld b,0
; first a byte token "O|LLL|MMMM" is read from the stream,
; where LLL is the number of literals and MMMM is
; a length of the match that follows after the literals
ReadToken: ld a,(hl) : exa : ld a,(hl) : inc hl
and #70 : jr z,NoLiterals
rrca : rrca : rrca : rrca ; LLL<7 means 0..6 literals...
cp #07 : call z,ReadLongBA ; LLL=7 means 7+ literals...
ld c,a : ldir
; next we read the low byte of the -offset
NoLiterals: push de : ld e,(hl) : inc hl : ld d,#FF
; the top bit of token is set if
; the offset contains the high byte as well
exa : or a : jp p,ShortOffset
LongOffset: ld d,(hl) : inc hl
; last but not least, the match length is read
ShortOffset: and #0F : add 3 ; MMMM<15 means match lengths 0+3..14+3
cp 15+3 : call z,ReadLongBA ; MMMM=15 means lengths 14+3+
ld c,a
ex (sp),hl : push hl ; BC = len, DE = -offset, HL = dest, SP ->[dest,src]
add hl,de : pop de ; BC = len, DE = dest, HL = dest+(-offset), SP->[src]
ldir : pop hl ; BC = 0, DE = dest, HL = src
jr ReadToken
; a standard routine to read extended codes
; into registers B (higher byte) and A (lower byte).
ReadLongBA: add (hl) : inc hl : ret nc
; the codes are designed to overflow;
; the overflow value 1 means read 1 extra byte
; and overflow value 0 means read 2 extra bytes
.code1: ld b,a : ld a,(hl) : inc hl : ret nz
.code0: ld c,a : ld b,(hl) : inc hl
; the two-byte match length equal to zero
; designates the end-of-data marker
or b : ld a,c : ret nz
pop de : pop de : ret