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module APULTRA
;
; Size-optimized ApLib decompressor by spke & uniabis (ver.04 01-07/06/2020, 139 bytes)
;
; The original Z80 decompressor for ApLib was written by Dan Weiss (Dwedit),
; then tweaked by Francisco Javier Pena Pareja (utopian),
; and optimized by Jaime Tejedor Gomez (Metalbrain).
;
; This version was heavily re-optimized for size by spke.
; (It is 17 bytes shorter and 22% faster than the 156b version by Metalbrain.)
;
; ver.00 by spke (21/08/2018-01/09/2018, 141 bytes);
; ver.01 by spke (spring 2019, 140(-1) bytes, slightly faster);
; ver.02 by spke (05-07/01/2020, added full revision history, support for long offsets
; and an option to use self-modifying code instead of IY)
; ver.03 by spke (18-29/05/2020, +0.5% speed, added support for backward compression)
; ver.04 by uniabis (01-07/06/2020, 139(-1) bytes, +1% speed, added support for HD64180)
;
; The data must be compressed using any compressor for ApLib capable of generating raw data.
; At present, two best available compressors are:
;
; "APC" by Sven-Ake Dahl: https://github.com/svendahl/cap or
; "apultra" by Emmanuel Marty: https://github.com/emmanuel-marty/apultra
;
; The compression can be done as follows:
;
; apc.exe e <sourcefile> <outfile>
; or
; apultra.exe <sourcefile> <outfile>
;
; A decent compressor was written by r57shell (although it is worse than compressors above):
; http://gendev.spritesmind.net/forum/viewtopic.php?p=32548#p32548
; The use of the official ApLib compressor by Joergen Ibsen is not recommended.
;
; The decompression is done in the standard way:
;
; ld hl,FirstByteOfCompressedData
; ld de,FirstByteOfMemoryForDecompressedData
; call DecompressApLib
;
; Backward decompression is also supported; you can compress files backward using:
;
; apultra.exe -b <sourcefile> <outfile>
;
; uncomment option "DEFINE BackwardDecompression" and decompress the resulting files using:
;
; ld hl,LastByteOfCompressedData
; ld de,LastByteOfMemoryForDecompressedData
; call DecompressApLib
;
; The decompressor modifies AF, AF', BC, DE, HL, IX.
;
; Of course, ApLib compression algorithms are (c) 1998-2014 Joergen Ibsen,
; see http://www.ibsensoftware.com/ 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 FasterGetBit ; 16% speed-up at the cost of extra 4 bytes
; DEFINE SupportLongOffsets ; +4 bytes for long offset support. slows decompression down by 1%, but may be needed to decompress files >=32K
; DEFINE BackwardDecompression ; decompress data compressed backwards, -5 bytes, speeds decompression up by 3%
IFDEF FasterGetBit
MACRO GET_BIT
add a : call z,ReloadByte
ENDM
ELSE
MACRO GET_BIT
call GetOneBit
ENDM
ENDIF
IFNDEF BackwardDecompression
MACRO NEXT_HL
inc hl
ENDM
MACRO COPY_1
ldi
ENDM
MACRO COPY_BC
ldir
ENDM
ELSE
MACRO NEXT_HL
dec hl
ENDM
MACRO COPY_1
ldd
ENDM
MACRO COPY_BC
lddr
ENDM
ENDIF
@DecompressApLib: ld a,128
;
; case "0"+BYTE: copy a single literal
CASE0: COPY_1 ; first byte is always copied as literal
ResetLWM: ld b,-1 ; LWM = 0 (LWM stands for "Last Was Match"; a flag that we did not have a match)
;
; main decompressor loop
MainLoop: GET_BIT : jr nc,CASE0 ; "0"+BYTE = copy literal
GET_BIT : jr nc,CASE10 ; "10"+gamma(offset/256)+BYTE+gamma(length) = the main matching mechanism
ld bc,%11100000
GET_BIT : jr nc,CASE110 ; "110"+[oooooool] = matched 2-3 bytes with a small offset
;
; case "111"+"oooo": copy a byte with offset -1..-15, or write zero to dest
CASE111:
ReadFourBits GET_BIT ; read short offset (4 bits)
rl c : jr c,ReadFourBits
ex de,hl : jr z,WriteZero ; zero offset means "write zero" (NB: B is zero here)
; "write a previous byte (1-15 away from dest)"
push hl ; BC = offset, DE = src, HL = dest
IFNDEF BackwardDecompression
sbc hl,bc ; HL = dest-offset (SBC works because branching above ensured NC)
ELSE
add hl,bc ; HL = dest-offset (SBC works because branching above ensured NC)
ENDIF
ld c,(hl) : pop hl
WriteZero ld (hl),c : NEXT_HL
ex de,hl : jr ResetLWM ; write one byte, reset LWM
;
; branch "110"+[oooooool]: copy two or three bytes (bit "l") with the offset -1..-127 (bits "ooooooo"), or stop
CASE110: ; "use 7 bit offset, length = 2 or 3"
; "if a zero is found here, it's EOF"
ld c,(hl) : rr c : ret z ; process EOF
NEXT_HL
push hl ; save src
ld h,b : ld l,c ; HL = offset
; flag NC means len=2, flag C means len=3
ld c,1 : rl c : jr SaveLWMOffset
;
; branch "10"+gamma(offset/256)+BYTE+gamma(length): the main matching mechanism
CASE10: ; save state of LWM into A'
exa : ld a,b : exa
; "use a gamma code * 256 for offset, another gamma code for length"
call GetGammaCoded
; the original decompressor contains
;
; if ((LWM == 0) && (offs == 2)) { ... }
; else {
; if (LWM == 0) { offs -= 3; }
; else { offs -= 2; }
; }
;
; so, the idea here is to use the fact that GetGammaCoded returns (offset/256)+2,
; and to split the first condition by noticing that C-1 can never be zero
exa : add c : ld c,a : exa
; "if gamma code is 2, use old r0 offset"
dec c : jr z,KickInLWM
dec c
ld b,c : ld c,(hl) : NEXT_HL ; BC = offset
push bc ; (SP) = offset
call GetGammaCoded ; BC = len*
ex (sp),hl ; HL = offset, (SP) = src
; interpretation of length value is offset-dependent
exa : ld a,h
IFDEF SupportLongOffsets
; NB offsets over 32000 require an additional check, which is skipped in most
; Z80 decompressors (seemingly as a performance optimization)
cp 32000/256 : jr nc,.Add2
ENDIF
cp 5 : jr nc,.Add1
or a : jr nz,.Add0
bit 7,l : jr nz,.Add0
.Add2 inc bc
.Add1 inc bc
.Add0 exa
SaveLWMOffset:
push hl : pop ix ; save offset for future LWMs
CopyMatch: ; this assumes that BC = len, DE = dest, HL = offset
; and also that (SP) = src, while having NC
IFNDEF BackwardDecompression
push de
ex de,hl : sbc hl,de ; HL = dest-offset
pop de ; DE = dest
ELSE
add hl,de ; HL = dest+offset
ENDIF
COPY_BC
pop hl ; recover src
jr MainLoop
;
; the re-use of the previous offset (LWM magic)
KickInLWM: ; "and a new gamma code for length"
call GetGammaCoded ; BC = len
push ix : ex (sp),hl ; DE = dest, HL = prev offset
jr CopyMatch
;
; interlaced gamma code reader
; x0 -> 1x
; x1y0 -> 1xy
; x1y1z0 -> 1xyz etc
; (technically, this is a 2-based variation of Exp-Golomb-1)
GetGammaCoded: ld bc,1
ReadGamma GET_BIT : rl c : rl b
GET_BIT : ret nc
jr ReadGamma
;
; pretty usual getbit for mixed datastreams
IFNDEF FasterGetBit
GetOneBit: add a : ret nz
ENDIF
ReloadByte: ld a,(hl) : NEXT_HL
rla : ret
endmodule