z80 branch, but with original (slightly more accurate) prob update

src/context_state.rs

@@ -33,13 +33,12 @@ impl<'a> Context<'a> {
 
     pub fn update(&mut self, bit: bool) {
         let old = self.state.contexts[self.index];
-        let offset = if !bit {
-            ONE_PROB as i32 >> UPDATE_RATE
+        if bit {
+            self.state.contexts[self.index] =
+                old - ((old as i32 + UPDATE_ADD) >> UPDATE_RATE) as u8;
         } else {
-            0
-        };
-
-        self.state.contexts[self.index] =
-            (offset + old as i32 - ((old as i32 + UPDATE_ADD) >> UPDATE_RATE)) as u8;
+            self.state.contexts[self.index] =
+                old + (((ONE_PROB as i32 - old as i32) + UPDATE_ADD) >> UPDATE_RATE) as u8;
+        }
     }
 }

src/main.rs

@@ -10,16 +10,12 @@ fn main() -> Result<()> {
         Some("pack") => {
             let level = args.opt_value_from_str(["-l", "--level"])?.unwrap_or(2u8);
             let use_bitstream = args.contains(["-b", "--bitstream"]);
-            let reverse = args.contains(["-r", "--reverse"]);
 
             let infile = args.free_from_os_str::<PathBuf, bool>(|s| Ok(s.into()))?;
             let outfile = args.free_from_os_str::<PathBuf, bool>(|s| Ok(s.into()))?;
 
             let mut data = vec![];
             File::open(infile)?.read_to_end(&mut data)?;
-            if reverse {
-                data.reverse();
-            }
 
             let mut pb = pbr::ProgressBar::new(data.len() as u64);
             pb.set_units(pbr::Units::Bytes);
@@ -43,18 +39,14 @@ fn main() -> Result<()> {
         }
         Some("unpack") => {
             let use_bitstream = args.contains(["-b", "--bitstream"]);
-            let reverse = args.contains(["-r", "--reverse"]);
 
             let infile = args.free_from_os_str::<PathBuf, bool>(|s| Ok(s.into()))?;
             let outfile = args.free_from_os_str::<PathBuf, bool>(|s| Ok(s.into()))?;
 
             let mut data = vec![];
             File::open(infile)?.read_to_end(&mut data)?;
-            let mut unpacked_data = upkr::unpack(&data, use_bitstream);
-            if reverse {
-                unpacked_data.reverse();
-            }
-            File::create(outfile)?.write_all(&unpacked_data)?;
+            let packed_data = upkr::unpack(&data, use_bitstream);
+            File::create(outfile)?.write_all(&packed_data)?;
         }
         Some(other) => {
             bail!("Unknown subcommand '{}'", other);

z80_unpacker/.gitignore

@@ -1,3 +1,4 @@
 *.bin
 *.tap
+*.sna
 *.lst

z80_unpacker/unpack.asm

@@ -12,15 +12,12 @@
 ;;     upkr.unpack
 ;;         IN: IX = packed data, DE' (shadow DE) = destination
 ;;         OUT: IX = after packed data
-;;         modifies: all registers except IY, requires 10 bytes of stack space
+;;         modifies: all registers except IY, requires 14 bytes of stack space
 ;;
 
     OPT push reset --syntax=abf
     MODULE upkr
 
-NUMBER_BITS     EQU     16+15       ; context-bits per offset/length (16+15 for 16bit offsets/pointers)
-    ; numbers (offsets/lengths) are encoded like: 1a1b1c1d1e0 = 0000'0000'001e'dbca
-
 /*
 u8* upkr_data_ptr;
 u8 upkr_probs[1 + 255 + 1 + 2*32 + 2*32];
@@ -84,8 +81,8 @@ unpack:
     ; BC = probs (context_index 0), state HL = 0, A' = 0x80 (no source bits left in upkr_current_byte)
 
   ; ** main loop to decompress data
-    ; D = prev_was_match = uninitialised, literal is expected first => will reset D to "false"
-    ; values for false/true of prev_was_match are: false = high(probs), true = 1 + high(probs)
+.decompress_data_reset_match:
+    ld      d,0                 ; prev_was_match = 0;
 .decompress_data:
     ld      c,0
     call    decode_bit          ; if(upkr_decode_bit(0))
@@ -102,22 +99,21 @@ unpack:
     ld      (de),a              ; *write_ptr++ = byte;
     inc     de
     exx
-    ld      d,b                 ; prev_was_match = false
-    jr      .decompress_data
+    jr      .decompress_data_reset_match
 
   ; * copy chunk of already decompressed data (match)
 .copy_chunk:
-    ld      a,b
     inc     b                   ; context_index = 256
         ;             if(prev_was_match || upkr_decode_bit(256)) {
         ;                 offset = upkr_decode_length(257) - 1;
         ;                 if (0 == offset) break;
         ;             }
+    xor     a
     cp      d                   ; CF = prev_was_match
     call    nc,decode_bit       ; if not prev_was_match, then upkr_decode_bit(256)
     jr      nc,.keep_offset     ; if neither, keep old offset
-    inc     c                   ; context_index to first "number" set for offsets decoding (257)
-    call    decode_number
+    inc     c
+    call    decode_length
     dec     de                  ; offset = upkr_decode_length(257) - 1;
     ld      a,d
     or      e
@@ -130,18 +126,18 @@ unpack:
         ;                 ++write_ptr;
         ;             }
         ;             prev_was_match = 1;
-    ld      c,low(257 + NUMBER_BITS)    ; context_index to second "number" set for lengths decoding
-    call    decode_number       ; length = upkr_decode_length(257 + 64);
+    ld      c,low(257+64)       ; context_index = 257+64
+    call    decode_length       ; length = upkr_decode_length(257 + 64);
     push    de
     exx
     ld      h,d                 ; DE = write_ptr
     ld      l,e
 .offset+*:  ld      bc,0
-    sbc     hl,bc               ; CF=0 from decode_number ; HL = write_ptr - offset
+    sbc     hl,bc               ; CF=0 from decode_length ; HL = write_ptr - offset
     pop     bc                  ; BC = length
     ldir
     exx
-    ld      d,b                 ; prev_was_match = true
+    ld      d,b                 ; prev_was_match = non-zero
     djnz    .decompress_data    ; adjust context_index back to 0..255 range, go to main loop
 
 /*
@@ -206,8 +202,9 @@ decode_bit:
     cp      l                       ; CF = bit = prob-1 < (upkr_state & 255) <=> prob <= (upkr_state & 255)
     inc     a
   ; ** adjust state
-    push    bc
-    ld      c,l                     ; C = (upkr_state & 255); (preserving the value)
+    push    af
+    push    af
+    push    hl
     push    af
     jr      nc,.bit_is_0
     neg                             ; A = -prob == (256-prob), CF=1 preserved
@@ -215,23 +212,28 @@ decode_bit:
     ld      d,0
     ld      e,a                     ; DE = state_scale ; prob || (256-prob)
     ld      l,d                     ; H:L = (upkr_state>>8) : 0
-    ld      b,8                     ; counter
+    ld      a,8                     ; counter
 .mulLoop:
     add     hl,hl
     jr      nc,.mul0
     add     hl,de
 .mul0:
-    djnz    .mulLoop                ; until HL = state_scale * (upkr_state>>8), also BC becomes (upkr_state & 255)
-    add     hl,bc                   ; HL = state_scale * (upkr_state >> 8) + (upkr_state & 255)
+    dec     a
+    jr      nz,.mulLoop             ; until HL = state_scale * (upkr_state>>8)
     pop     af
-    ld      d,-16                   ; D = -prob_offset (-16 0xF0 when bit = 0)
     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                       ; D = 0xFF (DE = -prob)
+    add     hl,de                   ; HL += -prob
+.bit_is_0_2:                        ; HL = state_offset + state_scale * (upkr_state >> 8)
+    pop     de
+    ld      d,0                     ; DE = (upkr_state & 255)
+    add     hl,de                   ; HL = state_offset + state_scale * (upkr_state >> 8) + (upkr_state & 255) ; new upkr_state
  ; *** adjust probs[context_index]
-    ld      e,a                     ; D:E = -prob_offset:prob, A = prob
+    pop     af                      ; restore prob and bit
+    ld      e,a
+    jr      c,.bit_is_1
+    ld      d,-16                   ; 0xF0
+.bit_is_1:                          ; D:E = -prob_offset:prob, A = prob
     and     $F8
     rra
     rra
@@ -240,10 +242,8 @@ decode_bit:
     adc     a,d                     ; A = -prob_offset + ((prob + 8) >> 4)
     neg
     add     a,e                     ; 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
+    pop     af                      ; restore resulting CF = bit
     pop     de
     ret
 
@@ -258,7 +258,7 @@ int upkr_decode_length(int context_index) {
     return length | (1 << bit_pos);
 }
 */
-decode_number:
+decode_length:
   ; HL = upkr_state
   ; IX = upkr_data_ptr
   ; BC = probs+context_index
@@ -291,7 +291,7 @@ decode_number:
     ENDIF
 
 probs:      EQU ($+255) & -$100                 ; probs array aligned to 256
-.real_c:    EQU 1 + 255 + 1 + 2*NUMBER_BITS     ; real size of probs array
+.real_c:    EQU 1 + 255 + 1 + 2*32 + 2*32       ; real size of probs array
 .c:         EQU (.real_c + 1) & -2              ; padding to even size (required by init code)
 .e:         EQU probs + .c