Update to v089r11 release.

byuu says:

Changelog:
- SPC7110 $480b (and its settings in $4805-6 + $4807) is now fully
  emulated
- decompressor restructured and commented accordingly

The final parts remaining for the SPC7110 core, all within the
decompression engine:
- need to detect when 15+ input bytes are read for one output byte and
  simulate a crash somehow (don't have to perfectly simulate corrupted
  data stream)
- need to emulate time required to decompress data (doesn't have to be
  perfect, just something other than instantaneous)
- need to determine what $480c status flags d6-d0 are for, as best we
  can anyway

bsnes/emulator/emulator.hpp

@@ -3,7 +3,7 @@
 
 namespace Emulator {
   static const char Name[] = "bsnes";
-  static const char Version[] = "089.10";
+  static const char Version[] = "089.11";
   static const char Author[] = "byuu";
   static const char License[] = "GPLv3";
 }

bsnes/sfc/chip/spc7110/dcu.cpp

@@ -16,68 +16,42 @@ void SPC7110::dcu_begin_transfer() {
 
   add_clocks(20);
   decompressor->initialize(dcu_mode, dcu_addr);
+  decompressor->decode();
 
-  if(r480b & 2) {
+  unsigned seek = r480b & 2 ? r4805 | r4806 << 8 : 0;
-    unsigned seek = (r4805 | r4806 << 8) << dcu_mode;
+  while(seek--) decompressor->decode();
-    add_clocks(seek);
-    while(seek--) decompressor->output();
-  }
 
   r480c |= 0x80;
+  dcu_offset = 0;
 }
 
 uint8 SPC7110::dcu_read() {
   if((r480c & 0x80) == 0) return 0x00;
-  return decompressor->output();
+
+  if(dcu_offset == 0) {
+    for(unsigned row = 0; row < 8; row++) {
+      switch(decompressor->bpp) {
+      case 1:
+        dcu_tile[row] = decompressor->result;
+        break;
+      case 2:
+        dcu_tile[row * 2 + 0] = decompressor->result >> 0;
+        dcu_tile[row * 2 + 1] = decompressor->result >> 8;
+        break;
+      case 4:
+        dcu_tile[row * 2 +  0] = decompressor->result >>  0;
+        dcu_tile[row * 2 +  1] = decompressor->result >>  8;
+        dcu_tile[row * 2 + 16] = decompressor->result >> 16;
+        dcu_tile[row * 2 + 17] = decompressor->result >> 24;
+        break;
       }
 
-/*
+      unsigned seek = r480b & 1 ? r4807 : 1;
-  unsigned tilesize = 8 << dcu_mode;
+      while(seek--) decompressor->decode();
-
-  if(dcu_sp == 0) {
-    unsigned tiles = r480b & 1 ? r4807 : 1;
-    for(unsigned tile = 0; tile < tiles; tile++) {
-      dcu_dp = tile * tilesize;
-      switch(dcu_mode) {
-      case 0: decompress_1bpp(); deinterleave_1bpp(tiles); break;
-      case 1: decompress_2bpp(); deinterleave_2bpp(tiles); break;
-      case 2: decompress_4bpp(); deinterleave_4bpp(tiles); break;
-      case 3: return 0x00;
-      }
     }
   }
 
-  uint8 data = dcu_output[dcu_sp++];
+  uint8 data = dcu_tile[dcu_offset++];
-  dcu_sp &= tilesize - 1;
+  dcu_offset &= 8 * decompressor->bpp - 1;
   return data;
-*/
-
-/*
-void SPC7110::deinterleave_1bpp(unsigned length) {
-  uint8 *target = dcu_output, *source = dcu_tiledata;
-  for(unsigned row = 0, sp = 0; row < 8; row++) {
-    target[row] = source[sp];
-    sp += length;
 }
-}
-
-void SPC7110::deinterleave_2bpp(unsigned length) {
-  uint8 *target = dcu_output, *source = dcu_tiledata;
-  for(unsigned row = 0, sp = 0; row < 8; row++) {
-    target[row * 2 + 0] = source[sp + 0];
-    target[row * 2 + 1] = source[sp + 1];
-    sp += 2 * length;
-  }
-}
-
-void SPC7110::deinterleave_4bpp(unsigned length) {
-  uint8 *target = dcu_output, *source = dcu_tiledata;
-  for(unsigned row = 0, sp = 0; row < 8; row++) {
-    target[row * 2 +  0] = source[sp +  0];
-    target[row * 2 +  1] = source[sp +  1];
-    target[row * 2 + 16] = source[sp + 16];
-    target[row * 2 + 17] = source[sp + 17];
-    sp = sp + 2 * length + 16 * ((sp + 2 * length) / 16 - sp / 16);
-  }
-}
-*/

bsnes/sfc/chip/spc7110/decompressor.cpp

@@ -7,17 +7,12 @@ struct Decompressor {
 
   Decompressor(SPC7110 &spc7110) : spc7110(spc7110) {}
 
-  uint8 input() {
+  uint8 read() {
     return spc7110.datarom_read(offset++);
   }
 
-  uint8 output() {
+  //inverse morton code transform: unpack big-endian packed pixels
-    if(cursor == 0) decompress();
+  //returns odd bits in lower half; even bits in upper half
-    uint8 data = tile[cursor++];
-    cursor &= 8 * bpp - 1;
-    return data;
-  }
-
   uint32 deinterleave(uint64 data, unsigned bits) {
     data = data & (1ull << bits) - 1;
     data = 0x5555555555555555ull & (data << bits | data >> 1);
@@ -28,6 +23,7 @@ struct Decompressor {
     return data | data >> 16;
   }
 
+  //extract a nibble and move it to the low four bits
   uint64 moveToFront(uint64 list, unsigned nibble) {
     for(uint64 n = 0, mask = ~15; n < 64; n += 4, mask <<= 4) {
       if((list >> n & 15) != nibble) continue;
@@ -38,21 +34,18 @@ struct Decompressor {
 
   void initialize(unsigned mode, unsigned origin) {
     for(auto &root : context) for(auto &node : root) node = {0, 0};
-    base = 0;
-    range = Max + 1;
     bpp = 1 << mode;
     offset = origin;
-    cursor = 0;
     bits = 8;
-    read = input();
+    range = Max + 1;
-    read = read << 8 | input();
+    input = read();
-    write = 0;
+    input = input << 8 | read();
+    output = 0;
     pixels = 0;
     colormap = 0xfedcba9876543210ull;
   }
 
-  void decompress() {
+  void decode() {
-    for(unsigned row = 0; row < 8; row++) {
     for(unsigned pixel = 0; pixel < 8; pixel++) {
       uint64 map = colormap;
       unsigned diff = 0;
@@ -64,10 +57,10 @@ struct Decompressor {
 
         if(pa != pb || pb != pc) {
           unsigned match = pa ^ pb ^ pc;
-            diff = 4;
+          diff = 4;                        //no match; all pixels differ
-            if((match ^ pc) == 0) diff = 3;
+          if((match ^ pc) == 0) diff = 3;  //a == b; pixel c differs
-            if((match ^ pb) == 0) diff = 2;
+          if((match ^ pb) == 0) diff = 2;  //c == a; pixel b differs
-            if((match ^ pa) == 0) diff = 1;
+          if((match ^ pa) == 0) diff = 1;  //b == c; pixel a differs
         }
 
         colormap = moveToFront(colormap, pa);
@@ -79,7 +72,7 @@ struct Decompressor {
 
       for(unsigned plane = 0; plane < bpp; plane++) {
         unsigned bit = bpp > 1 ? 1 << plane : 1 << (pixel & 3);
-          unsigned history = bit - 1 & write;
+        unsigned history = bit - 1 & output;
         unsigned set = 0;
 
         if(bpp == 1) set = pixel >= 4;
@@ -89,58 +82,41 @@ struct Decompressor {
         auto &ctx = context[set][bit + history - 1];
         auto &model = evolution[ctx.prediction];
         uint8 lps_offset = range - model.probability;
-          bool symbol = read >= (lps_offset << 8);
+        bool symbol = input >= (lps_offset << 8);  //test only the MSB
 
-          write = write << 1 | (symbol ^ ctx.swap);
+        output = output << 1 | (symbol ^ ctx.swap);
 
-          if(symbol == MPS) {
+        if(symbol == MPS) {          //[0 ... range-p]
-            range = lps_offset;
+          range = lps_offset;        //range = range-p
-          } else {
+        } else {                     //[range-p+1 ... range]
-            range -= lps_offset;
+          range -= lps_offset;       //range = p-1, with p < 0.75
-            read -= lps_offset << 8;
+          input -= lps_offset << 8;  //therefore, always rescale
-            base += lps_offset;
         }
 
-          while(range <= Max / 2) {
+        while(range <= Max / 2) {    //scale back into [0.75 ... 1.5]
           ctx.prediction = model.next[symbol];
 
           range <<= 1;
-            read <<= 1;
+          input <<= 1;
-            base <<= 1;
 
           if(--bits == 0) {
             bits = 8;
-              read += input();
+            input += read();
           }
         }
 
         if(symbol == LPS && model.probability > Half) ctx.swap ^= 1;
       }
 
-        unsigned index = write & (1 << bpp) - 1;
+      unsigned index = output & (1 << bpp) - 1;
       if(bpp == 1) index ^= pixels >> 15 & 1;
 
       pixels = pixels << bpp | (map >> 4 * index & 15);
     }
 
-      if(bpp == 1) {
+    if(bpp == 1) result = pixels;
-        tile[row] = pixels;
+    if(bpp == 2) result = deinterleave(pixels, 16);
-      }
+    if(bpp == 4) result = deinterleave(deinterleave(pixels, 32), 32);
-
-      if(bpp == 2) {
-        uint32 slice = deinterleave(pixels, 16);
-        tile[row * 2 + 0] = slice >> 0;
-        tile[row * 2 + 1] = slice >> 8;
-      }
-
-      if(bpp == 4) {
-        uint32 slice = deinterleave(deinterleave(pixels, 32), 32);
-        tile[row * 2 + 0x00] = slice >>  0;
-        tile[row * 2 + 0x01] = slice >>  8;
-        tile[row * 2 + 0x10] = slice >> 16;
-        tile[row * 2 + 0x11] = slice >> 24;
-      }
-    }
   }
 
   void serialize(serializer &s) {
@@ -151,44 +127,40 @@ struct Decompressor {
       }
     }
 
-    s.integer(base);
-    s.integer(range);
     s.integer(bpp);
     s.integer(offset);
-    s.integer(cursor);
     s.integer(bits);
-    s.integer(read);
+    s.integer(range);
-    s.integer(write);
+    s.integer(input);
+    s.integer(output);
     s.integer(pixels);
     s.integer(colormap);
-    s.array(tile);
+    s.integer(result);
   }
 
   enum : unsigned { MPS = 0, LPS = 1 };
   enum : unsigned { One = 0xaa, Half = 0x55, Max = 0xff };
 
   struct ModelState {
-    uint8 probability;
+    uint8 probability;  //of the more probable symbol (MPS)
-    uint8 next[2];
+    uint8 next[2];      //next state after output {MPS, LPS}
   };
   static ModelState evolution[53];
 
   struct Context {
-    uint8 prediction;
+    uint8 prediction;   //current model state
-    uint8 swap;
+    uint8 swap;         //if 1, exchange the role of MPS and LPS
-  } context[5][15];
+  } context[5][15];     //not all 75 contexts exists; this simplifies the code
 
-  uint8 base;
+  unsigned bpp;         //bits per pixel (1bpp = 1; 2bpp = 2; 4bpp = 4)
-  uint16 range;
+  unsigned offset;      //SPC7110 data ROM read offset
-  unsigned bpp;
+  unsigned bits;        //bits remaining in input
-  unsigned offset;
+  uint16 range;         //arithmetic range: technically 8-bits, but Max+1 = 256
-  unsigned cursor;
+  uint16 input;         //input data from SPC7110 data ROM
-  unsigned bits;
+  uint8 output;
-  uint16 read;
-  uint8 write;
   uint64 pixels;
-  uint64 colormap;
+  uint64 colormap;      //most recently used list
-  uint8 tile[32];
+  uint32 result;        //decompressed word after calling decode()
 };
 
 Decompressor::ModelState Decompressor::evolution[53] = {

bsnes/sfc/chip/spc7110/serialization.cpp

@@ -16,6 +16,8 @@ void SPC7110::serialize(serializer &s) {
   s.integer(dcu_pending);
   s.integer(dcu_mode);
   s.integer(dcu_addr);
+  s.integer(dcu_offset);
+  s.array(dcu_tile);
   decompressor->serialize(s);
 
   s.integer(r4810);

bsnes/sfc/chip/spc7110/spc7110.hpp

@@ -68,9 +68,9 @@ private:
   uint8 r4802;  //compression table B1
   uint7 r4803;  //compression table B2
   uint8 r4804;  //compression table index
-  uint8 r4805;  //decompression buffer index B0
+  uint8 r4805;  //adjust length B0
-  uint8 r4806;  //decompression buffer index B1
+  uint8 r4806;  //adjust length B1
-  uint8 r4807;  //deinterleave length
+  uint8 r4807;  //stride length
   uint8 r4809;  //compression counter B0
   uint8 r480a;  //compression counter B1
   uint8 r480b;  //decompression settings
@@ -79,6 +79,8 @@ private:
   bool dcu_pending;
   uint2 dcu_mode;
   uint23 dcu_addr;
+  unsigned dcu_offset;
+  uint8 dcu_tile[32];
   Decompressor *decompressor;
 
   //==============