Check in optimized-for-speed Z80 decompressor contributed by spke

2024-11-25 10:30:45 +00:00 · 2019-04-07 00:01:42 +02:00 · 2019-04-07 00:01:42 +02:00 · be54a4f889
commit be54a4f889
parent 6aa2dae4b3
1 changed files with 103 additions and 0 deletions
--- a/asm/z80/unlzsa_fast_v1.asm
+++ b/asm/z80/unlzsa_fast_v1.asm
@ -0,0 +1,103 @@
+;
+;  Speed-optimized LZSA decompressor by spke (v.1 03-05/04/2019, 122 bytes)
+;
+;  The data must be comressed 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 : jr ReadToken
+
+MoreLiterals:	; there are three possible situations here
+		; 1) a byte 0..253 is added to LLL and that is it or
+		; 2) a byte 254 is followed by another byte to add or
+		; 3) a byte 255 is followed by a word to be used
+		ld a,7 : add (hl) : inc hl : jp nc,CopyLiterals
+
+.Overflow	; we get here if the literals length byte plus 7 is greater than 255
+		inc b : cp 5 : jr c,CopyLiterals : jr nz,.Code255		; 5 is 7+254 modulo 256
+.Code254	add (hl) : inc hl : jr nc,CopyLiterals : inc b : jr CopyLiterals
+.Code255	ld c,(hl) : inc hl : ld b,(hl) : inc hl : jr CopyLiterals.UseC
+
+		; placed here this saves a JP per iteration
+CopyMatchNC	scf								; flag C for SBC HL,DE below must be set!!!
+CopyMatch:	ld c,a
+.UseC		ex (sp),hl : push hl						; BC = len, DE = offset, HL = dest, SP ->[dest,src]
+		sbc hl,de : pop de						; BC = len, DE = dest, HL = dest-offset, SP->[src]
+		ldir : pop hl							; BC = 0, DE = dest, HL = src
+	
+ReadToken:	; 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
+		ld a,(hl) : exa : ld a,(hl) : inc hl				; token is read twice to be re-used later
+		and #70 : jr z,NoLiterals
+
+		cp #70 : jr z,MoreLiterals					; LLL=7 means 7+ literals...
+		rrca : rrca : rrca : rrca					; LLL<7 means 0..6 literals...
+
+CopyLiterals:	ld c,a
+.UseC		ldir
+
+NoLiterals:	; next we read the first byte of the offset
+		push de : ld e,(hl) : inc hl
+		; the top bit of token is set if the offset contains two bytes
+		exa : and #8F : jp m,LongOffset
+
+ShortOffset:	ld d,b								; we keep B=0 for situations like this
+
+		; short matches have length 0+3..14+3
+ReadMatchLen:	add 3 : cp 15+3 : jp c,CopyMatch
+
+		; MMMM=15 indicates a multi-byte number of literals
+		; there are three possible situations here
+		; 1) a byte 0..253 is added to MMMM and that is it or
+		; 2) a byte 254 is followed by another byte to add or
+		; 3) a byte 255 is followed by a word to be used
+LongerMatch:	add (hl) : inc hl : jp nc,CopyMatchNC
+
+.Overflow	; we get here if the match length byte plus 15+3 is greater than 255
+		inc b : cp 16 : jr c,CopyMatch : jr nz,.Code255			; 16 is 15+3+254 modulo 256
+.Code254	add (hl) : inc hl : jr nc,CopyMatchNC : inc b : jr CopyMatch
+.Code255	ld c,(hl) : inc hl : ld b,(hl) : inc hl
+		; two-byte match length that is equal to zero is the marker for End-of-Data (EOD)
+.CheckEOD	ld a,b : or c : jr nz,CopyMatch.UseC
+		pop de : ret
+
+LongOffset:	; read second byte of the offset
+		ld d,(hl) : inc hl
+		add -128+3 : cp 15+3 : jp c,CopyMatch
+		add (hl) : inc hl : jp nc,CopyMatchNC
+		jr LongerMatch.Overflow
+
+