G2 support

src/import/Rom.lua

@@ -208,4 +208,103 @@ function Rom.decompressPic(data)
   return output, width
 end
 
+-- pokegold's "lz3" compression (home/decompress.asm), used for Gen 2
+-- graphics (tilesets, Pokemon pics, title screen art, ...).  `data` is a Lua
+-- array of bytes (as returned by Rom:bytes) or a raw string; returns a Lua
+-- array of decompressed bytes.  Ported instruction-for-instruction against
+-- pokegold's Decompress routine and cross-checked against tools/lzcompress.c
+-- (--uncompress path), which is the canonical reference for this format.
+local LZ_END = 0xFF
+local LZ_LITERAL   = 0
+local LZ_ITERATE   = 1
+local LZ_ALTERNATE = 2
+local LZ_ZERO      = 3
+local LZ_FLIP      = 5
+local LZ_REVERSE   = 6
+local LZ_LONG      = 7
+
+local function flipBits(value)
+  local flipped = 0
+  for bitIndex = 0, 7 do
+    flipped = flipped + math.floor(value / 2 ^ bitIndex) % 2 * 2 ^ (7 - bitIndex)
+  end
+  return flipped
+end
+
+function Rom.decompressLz3(data)
+  local bytes = data
+  if type(data) == "string" then
+    bytes = {}
+    for index = 1, #data do bytes[index] = data:byte(index) end
+  end
+
+  local pos = 1
+  local function nextByte()
+    local value = bytes[pos]
+    if not value then error("lz3 stream ended unexpectedly") end
+    pos = pos + 1
+    return value
+  end
+
+  local out = {}
+  while true do
+    local first = bytes[pos]
+    if not first then error("lz3 stream ended without a terminator") end
+    pos = pos + 1
+    if first == LZ_END then break end
+
+    local command, length
+    if math.floor(first / 0x20) == LZ_LONG then
+      -- 111xxxyy yyyyyyyy: xxx is the real command, yy.. is a 10-bit length
+      command = math.floor(first / 4) % 8
+      local high = first % 4
+      length = high * 0x100 + nextByte() + 1
+    else
+      command = math.floor(first / 0x20)
+      length = first % 0x20 + 1
+    end
+
+    if command == LZ_LITERAL then
+      for _ = 1, length do out[#out + 1] = nextByte() end
+    elseif command == LZ_ITERATE then
+      local value = nextByte()
+      for _ = 1, length do out[#out + 1] = value end
+    elseif command == LZ_ALTERNATE then
+      local a, b = nextByte(), nextByte()
+      for index = 1, length do
+        out[#out + 1] = (index % 2 == 1) and a or b
+      end
+    elseif command == LZ_ZERO then
+      for _ = 1, length do out[#out + 1] = 0 end
+    else
+      -- Lookback commands (LZ_REPEAT/LZ_FLIP/LZ_REVERSE, and the unused id
+      -- 7 which the hardware routine falls through to LZ_REPEAT for).
+      -- A high-bit offset byte is a 7-bit negative lookback from the
+      -- current output position; otherwise it is a 15-bit absolute offset
+      -- from the start of the output buffer (two bytes, big-endian).
+      local offsetByte = nextByte()
+      local from
+      if offsetByte >= 0x80 then
+        from = #out - (offsetByte % 0x80)
+      else
+        from = offsetByte * 0x100 + nextByte() + 1
+      end
+      if command == LZ_FLIP then
+        for index = 0, length - 1 do
+          out[#out + 1] = flipBits(out[from + index])
+        end
+      elseif command == LZ_REVERSE then
+        for index = 0, length - 1 do
+          out[#out + 1] = out[from - index]
+        end
+      else
+        for index = 0, length - 1 do
+          out[#out + 1] = out[from + index]
+        end
+      end
+    end
+  end
+  return out
+end
+
 return Rom