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unlzsa1_small.asm
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;
; Size-optimized LZSA1 decompressor by spke & uniabis (67 bytes)
;
; ver.00 by spke for LZSA 0.5.4 (23/04/2019, 69 bytes);
; ver.01 by spke for LZSA 1.0.5 (24/07/2019, added support for backward decompression);
; ver.02 by uniabis (30/07/2019, 68(-1) bytes, +3.2% speed);
; ver.03 by spke for LZSA 1.0.7 (31/07/2019, small re-organization of macros);
; ver.04 by spke (06/08/2019, 67(-1) bytes, -1.2% speed);
; ver.05 by spke for LZSA 1.1.0 (25/09/2019, added full revision history)
;
; The data must be compressed using the command line compressor by Emmanuel Marty
; The compression is done as follows:
;
; lzsa.exe -f1 -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,FirstByteOfCompressedData
; ld de,FirstByteOfMemoryForDecompressedData
; call DecompressLZSA1
;
; Backward compression is also supported; you can compress files backward using:
;
; lzsa.exe -f1 -r -b <sourcefile> <outfile>
;
; and decompress the resulting files using:
;
; ld hl,LastByteOfCompressedData
; ld de,LastByteOfMemoryForDecompressedData
; call DecompressLZSA1
;
; (do not forget to uncomment the BACKWARD_DECOMPRESS option in the decompressor).
;
; Of course, LZSA compression algorithms are (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.
; DEFINE BACKWARD_DECOMPRESS
IFNDEF BACKWARD_DECOMPRESS
MACRO NEXT_HL
inc hl
ENDM
MACRO ADD_OFFSET
ex de,hl : add hl,de
ENDM
MACRO BLOCKCOPY
ldir
ENDM
ELSE
MACRO NEXT_HL
dec hl
ENDM
MACRO ADD_OFFSET
push hl : or a : sbc hl,de : pop de ; 11+4+15+10 = 40t / 5 bytes
ENDM
MACRO BLOCKCOPY
lddr
ENDM
ENDIF
@DecompressLZSA1:
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) : NEXT_HL : push af
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 : BLOCKCOPY
; next we read the low byte of the -offset
NoLiterals: pop af : push de : ld e,(hl) : NEXT_HL : ld d,#FF
; the top bit of token is set if
; the offset contains the high byte as well
or a : jp p,ShortOffset
LongOffset: ld d,(hl) : NEXT_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 ; BC = len, DE = -offset, HL = dest, SP -> [src]
ADD_OFFSET ; BC = len, DE = dest, HL = dest+(-offset), SP -> [src]
BLOCKCOPY ; BC = 0, DE = dest
pop hl : jr ReadToken ; HL = src
; a standard routine to read extended codes
; into registers B (higher byte) and A (lower byte).
ReadLongBA: add (hl) : NEXT_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) : NEXT_HL : ret nz
.code0: ld c,a : ld b,(hl) : NEXT_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