From 3c773aca8d0f886930e61e13784fb3ec87519c55 Mon Sep 17 00:00:00 2001
From: "Peter Helcmanovsky (Ped)" <ped@7gods.org>
Date: Fri, 16 Sep 2022 02:50:23 +0200
Subject: [PATCH 1/4] z80_unpacker: add performance variant of depacker

---
 z80_unpacker/unpack.asm | 19 +++++++++++++++++++
 1 file changed, 19 insertions(+)

diff --git a/z80_unpacker/unpack.asm b/z80_unpacker/unpack.asm
index 6dc9097..c788a70 100644
--- a/z80_unpacker/unpack.asm
+++ b/z80_unpacker/unpack.asm
@@ -15,6 +15,8 @@
 ;;         modifies: all registers except IY, requires 10 bytes of stack space
 ;;
 
+;     DEFINE UPKR_UNPACK_SPEED        ; uncomment to get larger but faster unpack routine
+
     OPT push reset --syntax=abf
     MODULE upkr
 
@@ -215,6 +217,10 @@ decode_bit:
     ld      d,0
     ld      e,a                     ; DE = state_scale ; prob || (256-prob)
     ld      l,d                     ; H:L = (upkr_state>>8) : 0
+
+  IFNDEF UPKR_UNPACK_SPEED
+    ;; looped MUL for minimum unpack size
+
     ld      b,8                     ; counter
 .mulLoop:
     add     hl,hl
@@ -222,6 +228,19 @@ decode_bit:
     add     hl,de
 .mul0:
     djnz    .mulLoop                ; until HL = state_scale * (upkr_state>>8), also BC becomes (upkr_state & 255)
+  ELSE
+    ;;; unrolled MUL for better performance, +25 bytes unpack size
+
+    ld      b,d
+    DUP     8
+        add     hl,hl
+        jr      nc,000_f
+        add     hl,de
+000:
+    EDUP
+
+  ENDIF
+
     add     hl,bc                   ; HL = state_scale * (upkr_state >> 8) + (upkr_state & 255)
     pop     af
     ld      d,-16                   ; D = -prob_offset (-16 0xF0 when bit = 0)

From b13fa05413a11686604240753f154b62bd5259ff Mon Sep 17 00:00:00 2001
From: "Peter Helcmanovsky (Ped)" <ped@7gods.org>
Date: Sun, 18 Sep 2022 00:23:14 +0200
Subject: [PATCH 2/4] z80_unpacker: add backward variant of unpacker + example
 extended

---
 z80_unpacker/example/example.asm              |  77 +++++++++++++++---
 z80_unpacker/example/example.sna              | Bin 49179 -> 49179 bytes
 .../Grongy - ZX Spectrum (2022).scr.upk       | Bin 0 -> 1760 bytes
 .../Schafft - Poison (2017).scr.upk           | Bin 0 -> 1400 bytes
 .../diver - Back to Bjork (2015).scr.upk      | Bin 0 -> 2869 bytes
 ... (Forever 2014 Olympic Edition, 1).scr.upk | Bin 0 -> 4294 bytes
 z80_unpacker/unpack.asm                       |  24 ++++--
 7 files changed, 80 insertions(+), 21 deletions(-)
 create mode 100644 z80_unpacker/example/screens.reversed/Grongy - ZX Spectrum (2022).scr.upk
 create mode 100644 z80_unpacker/example/screens.reversed/Schafft - Poison (2017).scr.upk
 create mode 100644 z80_unpacker/example/screens.reversed/diver - Back to Bjork (2015).scr.upk
 create mode 100644 z80_unpacker/example/screens.reversed/diver - Mercenary 4. The Heaven's Devil (2014) (Forever 2014 Olympic Edition, 1).scr.upk

diff --git a/z80_unpacker/example/example.asm b/z80_unpacker/example/example.asm
index 80fd790..e3e6570 100644
--- a/z80_unpacker/example/example.asm
+++ b/z80_unpacker/example/example.asm
@@ -3,7 +3,8 @@
     DEVICE ZXSPECTRUM48,$8FFF
 
     ORG     $9000
-compressed_scr_files:       ; border color byte + upkr-packed .scr file
+  ;; forward example data
+compressed_scr_files.fwd:               ; border color byte + upkr-packed .scr file
     DB      1
     INCBIN  "screens/Grongy - ZX Spectrum (2022).scr.upk"
     DB      7
@@ -13,37 +14,87 @@ compressed_scr_files:       ; border color byte + upkr-packed .scr file
     DB      6
     INCBIN  "screens/diver - Back to Bjork (2015).scr.upk"
 .e:
+  ;; backward example data (unpacker goes from the end of the data!)
+compressed_scr_files.rwd.e: EQU $-1     ; the final IX will point one byte ahead of "$" here
+    INCBIN  "screens.reversed/diver - Back to Bjork (2015).scr.upk"
+    DB      6
+    INCBIN  "screens.reversed/diver - Mercenary 4. The Heaven's Devil (2014) (Forever 2014 Olympic Edition, 1).scr.upk"
+    DB      0
+    INCBIN  "screens.reversed/Schafft - Poison (2017).scr.upk"
+    DB      7
+    INCBIN  "screens.reversed/Grongy - ZX Spectrum (2022).scr.upk"
+compressed_scr_files.rwd:               ; border color byte + upkr-packed .scr file (backward)
+    DB      1
 
 start:
     di
 ;     OPT --zxnext
-;     nextreg 7,3                 ; ZX Next: switch to 28Mhz
-    ld      ix,compressed_scr_files
-.slideshow_loop
+;     nextreg 7,3                       ; ZX Next: switch to 28Mhz
+
+  ;;; FORWARD packed/unpacked data demo
+    ld      ix,compressed_scr_files.fwd
+.slideshow_loop.fwd:
   ; set BORDER for next image
-    ldi     a,(ix)              ; fake: ld a,(ix) : inc ix
+    ld      a,(ix)
+    inc     ix
     out     (254),a
   ; call unpack of next image directly into VRAM
-    ld      de,$4000            ; target VRAM
+    ld      de,$4000                    ; target VRAM
     exx
   ; IX = packed data, DE' = destination ($4000)
   ; returned IX will point right after the packed data
-    call    upkr.unpack
+    call    fwd.upkr.unpack
   ; do some busy loop with CPU to delay between images
+    call    delay
+  ; check if all images were displayed, loop around from first one then
+    ld      a,ixl
+    cp      low compressed_scr_files.fwd.e
+    jr      nz,.slideshow_loop.fwd
+
+  ;;; BACKWARD packed/unpacked data demo
+    ld      ix,compressed_scr_files.rwd
+.slideshow_loop.rwd:
+  ; set BORDER for next image
+    ld      a,(ix)
+    dec     ix
+    out     (254),a
+  ; call unpack of next image directly into VRAM
+    ld      de,$5AFF                    ; target VRAM
+    exx
+  ; IX = packed data, DE' = destination
+  ; returned IX will point right ahead of the packed data
+    call    rwd.upkr.unpack
+  ; do some busy loop with CPU to delay between images
+    call    delay
+  ; check if all images were displayed, loop around from first one then
+    ld      a,ixl
+    cp      low compressed_scr_files.rwd.e
+    jr      nz,.slideshow_loop.rwd
+
+    jr      start
+
+delay:
     ld      bc,$AA00
 .delay:
     .8 ex      (sp),ix
     dec     c
     jr      nz,.delay
     djnz    .delay
-  ; check if all images were displayed, loop around from first one then
-    ld      a,ixl
-    cp      low compressed_scr_files.e
-    jr      z,start
-    jr      .slideshow_loop
+    ret
 
   ; include the depacker library, optionally putting probs array buffer near end of RAM
     DEFINE  UPKR_PROBS_ORIGIN $FA00   ; if not defined, array will be put after unpack code
-    INCLUDE "../unpack.asm"
+
+    MODULE fwd
+        INCLUDE "../unpack.asm"
+    ENDMODULE
+
+    MODULE rwd
+        DEFINE BACKWARDS_UNPACK         ; defined to build backwards unpack
+                ; initial IX points at last byte of compressed data
+                ; initial DE' points at last byte of unpacked data
+
+        INCLUDE "../unpack.asm"
+    ENDMODULE
 
     SAVESNA "example.sna",start
diff --git a/z80_unpacker/example/example.sna b/z80_unpacker/example/example.sna
index a1f9f56b4e1b2fcf97dd33ac8ef27758dea43e6a..78df3d8a2cf9da82d8237271b0d006240e53706b 100644
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diff --git a/z80_unpacker/example/screens.reversed/Grongy - ZX Spectrum (2022).scr.upk b/z80_unpacker/example/screens.reversed/Grongy - ZX Spectrum (2022).scr.upk
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diff --git a/z80_unpacker/example/screens.reversed/Schafft - Poison (2017).scr.upk b/z80_unpacker/example/screens.reversed/Schafft - Poison (2017).scr.upk
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new file mode 100644
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z(6k~w+GBgqX)Sr19GH*&R3w--!sSkuq@7UZkS~)Yjyy=RtBvB(M@K^H(xtZ8+P9Ko
zr+=v5#dm%frnmcwyBa<7@w6caTo?)D*lz>^zdN70m@U>QB}DA)_j3Ompu#kuIl5<M
zY`(jL`~k9-vTNTGI(llF7YB);qh4oaX6}<z&);(*<Qv|t%)JjN(w+wm4GhvYg*!Q>
z9uc6{&_=vgAb7ui4Tk+dPQz1)ThVf-+$BiX!%+!xBMMz3yJvAV?XlIf&j_9+63nus
zNJ?r?86@Wwg5Y0^V-lt<F>ua~?RX=wGq-Gf<v|KZgki5aafAW$2?pD9wk?u}VQ2=&
zf&5F1Uk$>)dyR?U3PgYwHcg0{$a4-kN>FJ_w(Ll;DL!i`dZa%`8e_Pc%2?Qu9KUV3
zht2BCw^hgRZLz$2uDF4;RQrW)zZbY}(|Q4i4$92u>P31{lI_qw2P{$$xWs7wfu3ze
zcZyZW-Q3$-;WR7!?cLtUcPQMf#=;X0vtTlvyDcUmaw_o()e?>{-^~=3OX(yhFYvm5
zQ%{&Q{QJmYHM<-ZnW8-ueJrS@Rb)+j94no!;hVXwmoO`7a(Y?ZjRB5tlw5F;@Okt7
zDlHcjv{M2Afu&E1eUJH@yGu#q!VaTR9MrAWrW))YfC^Mi%i!LN=b=)?z|Q59nAqDu
z@4)PYsK5Z&(-v^R&lZZkxqk}H5^I!`cC!H7YWa|X_LUz?wrm}M(%zFx8nuu`Nvpg+
zDZv+y{=)z1=cuR)oY`)A25|;ppiGg8^sIfKa`p8gbj{A%g`LLjf1E{Uyumr)dIuwP
zxen}9I>+Fjsh*kRYJ5L&-P8x^+(qRaypE@eIE|>Nu>+UdjDy_LjE`>K;{V4#6a%fy
zok5XK=DUC+ISQ9zM&Mc|LDt8w7OLJ!j1}Q5AryNST&v3`wIyaV3D}jXa8$KIX2nMV
zj*_ZWH-dgG{`$a%wlDn;+%d;WbH$(}c@Muzau+dKBIgtsj^8vRE=~NRXs?=(lcoE3
zIAGh;i~<v0z@^ejihaP$30}Z1xrL`@E8@lGG?beN^_Dtxt?>5%_})2bl>W?VG1z2+
z0jlqc9%m-qNxBk6+aJA)tQ*UuBZ(`lX|i}K`B&rrEMxBqN;TrgF&VOcL6hrqS%FaB
z3rbFJ-;kR0on2cxld#Ci;F=9@uHToK-EH0<U8~wNBX7w)dzCprVzYE=UbLZ&_V<H9
zW&0xf)Euh8frgIr?@MfGi>HByRhLkiZd3EFD!DdxZyz@Nf|O}?(~C+`oyHYtkBa;1
z#D|nnou8a4%t1{+m)RWvbd@nbQQtC+*sQEtq6qnL`}ml`p}oV$URsPbg7Fi~{1<Z8
zXu}lYouEQ)2|{4rbGv*`-~3N1j}CdS4{Zr0{f|JX#C8S2Jr&s9<Gr-8{z4C->Qeak
zO@-A!xMjJ7*9IT^i&xk_J4kud**ulu@dv&(T-C}GsKkg~v0Iwmm1D9ucP3GXLD>ql
z*uiv5D!`&T4j8Uvlq0%<&3bv5PgjV6*Ojw1<C$Yk<7=eFkS<L?EylDVp3O>}7>js6
zV-EqYhZEDcV|T8oFV#{VQ(ruV4a0xpDU^nHQnLPUDf6xai=nSm6H`hZ=ZYz?djkre
zKAE|tGyb71!qENNfP{tW_rSCPr5h3ufU;2B;F$`P?^!a)k}PhdLt42n?ipF)8&j$T
zWZBG1Gxdgg1xb%CvKkv~=Z+&FQgI25f0a+~8?DvCCQ>H0MayBg!hb90#Vk8`K#-}>
z2$e7H8KW?c(bw~&a;m&hn9;Kb@i%*Fj?G<K>AsUTg{5OhDdVZR@8MOe#%jF(EgjXB
z#qMN@*IsXwqv1~NHeavbTW=;yWOy)VUock9eeP@rg4Pw(uB=s$0YZg_BrUvLZsVq$
zr$|!xIO=9f^JOi!i7XkqBPBbH5bP&@TiYV)9})BIr>#l1v@RL72cM{b6qQDe7itEI
zIJAK`z1cWy^>O2LI)yzrM(s%{E!skxfgtV)66_B94V+Sahb?V&AYT`?n6d+ugg*50
zyJNJKvud%cG$~ba|7yiv9rj_nHbK8fD{6T-j{2iLJDtFRf<ZA}FkzC~GKN1foH9|9
z&~+`<o7WW6o+v|ld1Q2_({cX#c5L?+El9CEz+H2SYNVmYI-GVYZv8&TPuI|?b_i%Q
oe=*6zR1`xf99p@8_8LoBDH3rvJai;^GXv{Dxv$n})ZYPo0SI?;zW@LL

literal 0
HcmV?d00001

diff --git a/z80_unpacker/unpack.asm b/z80_unpacker/unpack.asm
index c788a70..b7e5120 100644
--- a/z80_unpacker/unpack.asm
+++ b/z80_unpacker/unpack.asm
@@ -15,6 +15,10 @@
 ;;         modifies: all registers except IY, requires 10 bytes of stack space
 ;;
 
+;     DEFINE BACKWARDS_UNPACK         ; uncomment to build backwards depacker
+            ; initial IX points at last byte of compressed data
+            ; initial DE' points at last byte of unpacked data
+
 ;     DEFINE UPKR_UNPACK_SPEED        ; uncomment to get larger but faster unpack routine
 
     OPT push reset --syntax=abf
@@ -102,7 +106,7 @@ unpack:
     ld      a,c
     exx
     ld      (de),a              ; *write_ptr++ = byte;
-    inc     de
+    IFNDEF BACKWARDS_UNPACK : inc de : ELSE : dec de : ENDIF
     exx
     ld      d,b                 ; prev_was_match = false
     jr      .decompress_data
@@ -139,9 +143,13 @@ unpack:
     ld      h,d                 ; DE = write_ptr
     ld      l,e
 .offset+*:  ld      bc,0
+    IFNDEF BACKWARDS_UNPACK
     sbc     hl,bc               ; CF=0 from decode_number ; HL = write_ptr - offset
+    ELSE
+    add     hl,bc               ; HL = write_ptr + offset
+    ENDIF
     pop     bc                  ; BC = length
-    ldir
+    IFNDEF BACKWARDS_UNPACK : ldir : ELSE : lddr : ENDIF
     exx
     ld      d,b                 ; prev_was_match = true
     djnz    .decompress_data    ; adjust context_index back to 0..255 range, go to main loop
@@ -195,7 +203,7 @@ decode_bit:
     jr      nz,.has_bit             ; CF=data, ZF=0 -> some bits + stop bit still available
   ; CF=1 (by stop bit)
     ld      a,(ix)
-    inc     ix                      ; upkr_current_byte = *upkr_data_ptr++;
+    IFNDEF BACKWARDS_UNPACK : inc ix : ELSE : dec ix : ENDIF    ; upkr_current_byte = *upkr_data_ptr++;
     adc     a,a                     ; CF=data, b0=1 as new stop bit
 .has_bit:
     adc     hl,hl                   ; upkr_state = (upkr_state << 1) + (upkr_current_byte >> 7);
@@ -306,12 +314,12 @@ decode_number:
     ; reserve space for probs array without emitting any machine code (using only EQU)
 
     IFDEF UPKR_PROBS_ORIGIN     ; if specific address is defined by user, move probs array there
-    ORG UPKR_PROBS_ORIGIN
+probs:      EQU ((UPKR_PROBS_ORIGIN) + 255) & -$100     ; probs array aligned to 256
+    ELSE
+probs:      EQU ($ + 255) & -$100                       ; probs array aligned to 256
     ENDIF
-
-probs:      EQU ($+255) & -$100                 ; probs array aligned to 256
-.real_c:    EQU 1 + 255 + 1 + 2*NUMBER_BITS     ; real size of probs array
-.c:         EQU (.real_c + 1) & -2              ; padding to even size (required by init code)
+.real_c:    EQU 1 + 255 + 1 + 2*NUMBER_BITS             ; real size of probs array
+.c:         EQU (.real_c + 1) & -2                      ; padding to even size (required by init code)
 .e:         EQU probs + .c
 
     DISPLAY "upkr.unpack probs array placed at: ",/A,probs,",\tsize: ",/A,probs.c

From d4bce4bf7cb1095a797ca5853c0c01fcba4f603f Mon Sep 17 00:00:00 2001
From: "Peter Helcmanovsky (Ped)" <ped@7gods.org>
Date: Sun, 18 Sep 2022 22:54:10 +0200
Subject: [PATCH 3/4] z80_unpacker: optimisation: -3B and ~-10T in decode_bit =
 174B

unpack zx48.rom is now ~22.6s (from 23.0s)
(performance version is now 199 bytes, zx48.rom unpack 19.4s -> 19.0s)
---
 z80_unpacker/example/example.sna | Bin 49179 -> 49179 bytes
 z80_unpacker/unpack.asm          |  31 +++++++++++++++----------------
 2 files changed, 15 insertions(+), 16 deletions(-)

diff --git a/z80_unpacker/example/example.sna b/z80_unpacker/example/example.sna
index 78df3d8a2cf9da82d8237271b0d006240e53706b..515f5d68690562b02a92e501cbcea636569d53df 100644
GIT binary patch
delta 175
zcmbQ;z&yKwd4u>u#tV}r7KZU{eJEYE`NZ4c^oM*3XSYtSS!ge8z$7XeFaPY1yuAFm
z50l@z9As*md~u<Hj{GAF0iLt+k4_63{H(kwBz-eL;$;QPt}F7740w3XCOv`}B>D(w
zP|{@GMM_Mnk0vi%C}n`fyo)CV|JO@!f=!b;Ee)bAKG~lJGA(|d+^G0Ve51i5mdPdi
GmjeKk{!YRG

delta 167
zcmbQ;z&yKwd4u>u#><l>7KZWdcqm=9`NZ4c^oM*3XLn4lS!gdN_Q8NTKvgpS*$;Uj
z=z8nYe2}The)74620BWQEChJYDm^+aXz;W0rjYc_0Ew3sEW55KJu=|oIh*kaVwS`s
upjjD{wH7HcX*`;|aG{h2b|WvI6#QQ=!3j1{>a;YF-rT$Bq0Hox{mTKZu}H!I

diff --git a/z80_unpacker/unpack.asm b/z80_unpacker/unpack.asm
index b7e5120..b1bcbce 100644
--- a/z80_unpacker/unpack.asm
+++ b/z80_unpacker/unpack.asm
@@ -250,27 +250,26 @@ decode_bit:
   ENDIF
 
     add     hl,bc                   ; HL = state_scale * (upkr_state >> 8) + (upkr_state & 255)
-    pop     af
-    ld      d,-16                   ; D = -prob_offset (-16 0xF0 when bit = 0)
+    pop     af                      ; restore prob and CF=bit
     jr      nc,.bit_is_0_2
-    ld      d,b                     ; D = -prob_offset (0 when bit = 1) (also does fix following ADD)
-    dec     h
-    add     hl,de                   ; HL += -prob (HL += (256 - prob) - 256)
-.bit_is_0_2:                        ; HL = state_offset + state_scale * (upkr_state >> 8) + (upkr_state & 255) ; new upkr_state
+    dec     d                       ; DE = -prob (also D = bit ? $FF : $00)
+    add     hl,de                   ; HL += -prob
+    ; ^ this always preserves CF=1, because (state>>8) >= 128, state_scale: 7..250, prob: 7..250,
+    ; so 7*128 > 250 and thus edge case `ADD hl=(7*128+0),de=(-250)` => CF=1
+.bit_is_0_2:
  ; *** adjust probs[context_index]
-    ld      e,a                     ; D:E = -prob_offset:prob, A = prob
-    and     $F8
+    ld      e,a                     ; preserve prob
+    rra                             ; + (bit<<4) ; part of -prob_offset, needs another -16
+    and     $FC                     ; clear/keep correct bits to get desired (prob>>4) + extras, CF=0
     rra
     rra
-    rra
-    rra
-    adc     a,d                     ; A = -prob_offset + ((prob + 8) >> 4)
-    neg
-    add     a,e                     ; A = prob_offset + prob - ((prob + 8) >> 4)
+    rra                             ; A = (bit<<4) + (prob>>4), CF=(prob & 8)
+    adc     a,-16                   ; A = (bit<<4) - 16 + ((prob + 8)>>4) ; -prob_offset = (bit<<4) - 16
+    sub     e                       ; A = (bit<<4) - 16 + ((prob + 8)>>4) - prob ; = ((prob + 8)>>4) - prob_offset - prob
+    neg                             ; A = prob_offset + prob - ((prob + 8)>>4)
     pop     bc
-    ld      (bc),a                  ; update probs[context_index]
-    add     a,d                     ; bit=0: A = 23..249, D = 240 -> CF=1 || bit=1: D=0 -> CF=0
-    ccf                             ; resulting CF = bit restored
+    ld      (bc),a                  ; probs[context_index] = prob_offset + prob - ((prob + 8) >> 4);
+    add     a,d                     ; restore CF = bit (D = bit ? $FF : $00 && A > 0)
     pop     de
     ret
 

From 165f593a11f176c544cfda0a6dcd9614d47671d1 Mon Sep 17 00:00:00 2001
From: "Peter Helcmanovsky (Ped)" <ped@7gods.org>
Date: Sun, 18 Sep 2022 23:04:37 +0200
Subject: [PATCH 4/4] z80_unpacker: (codestyle) whitespace + temporary label
 rename

---
 z80_unpacker/unpack.asm | 11 ++++++-----
 1 file changed, 6 insertions(+), 5 deletions(-)

diff --git a/z80_unpacker/unpack.asm b/z80_unpacker/unpack.asm
index b1bcbce..26e47b7 100644
--- a/z80_unpacker/unpack.asm
+++ b/z80_unpacker/unpack.asm
@@ -227,8 +227,8 @@ decode_bit:
     ld      l,d                     ; H:L = (upkr_state>>8) : 0
 
   IFNDEF UPKR_UNPACK_SPEED
-    ;; looped MUL for minimum unpack size
 
+    ;; looped MUL for minimum unpack size
     ld      b,8                     ; counter
 .mulLoop:
     add     hl,hl
@@ -236,15 +236,16 @@ decode_bit:
     add     hl,de
 .mul0:
     djnz    .mulLoop                ; until HL = state_scale * (upkr_state>>8), also BC becomes (upkr_state & 255)
-  ELSE
-    ;;; unrolled MUL for better performance, +25 bytes unpack size
 
+  ELSE
+
+    ;;; unrolled MUL for better performance, +25 bytes unpack size
     ld      b,d
     DUP     8
         add     hl,hl
-        jr      nc,000_f
+        jr      nc,0_f
         add     hl,de
-000:
+0:
     EDUP
 
   ENDIF