1 files changed, 94 insertions, 24 deletions

diff --git a/common/huffman.h b/common/huffman.h
index b4de5ab483..052c7bf825 100644
--- a/common/huffman.h
+++ b/common/huffman.h
@@ -20,7 +20,7 @@
  *
  */
 
-// Based on eos' Huffman code
+// Based on xoreos' Huffman code
 
 #ifndef COMMON_HUFFMAN_H
 #define COMMON_HUFFMAN_H
@@ -31,12 +31,22 @@
 
 namespace Common {
 
+inline uint32 REVERSEBITS(uint32 x) {
+	x = (((x & ~0x55555555) >> 1) | ((x & 0x55555555) << 1));
+	x = (((x & ~0x33333333) >> 2) | ((x & 0x33333333) << 2));
+	x = (((x & ~0x0F0F0F0F) >> 4) | ((x & 0x0F0F0F0F) << 4));
+	x = (((x & ~0x00FF00FF) >> 8) | ((x & 0x00FF00FF) << 8));
+
+	return((x >> 16) | (x << 16));
+}
+
 /**
  * Huffman bitstream decoding
  *
  * Used in engines:
  *  - scumm
  */
+template<class BITSTREAM>
 class Huffman {
 public:
 	/** Construct a Huffman decoder.
@@ -48,47 +58,107 @@ public:
 	 *  @param symbols The symbols. If 0, assume they are identical to the code indices.
 	 */
 	Huffman(uint8 maxLength, uint32 codeCount, const uint32 *codes, const uint8 *lengths, const uint32 *symbols = nullptr);
-	~Huffman();
-
-	/** Modify the codes' symbols. */
-	void setSymbols(const uint32 *symbols = nullptr);
 
 	/** Return the next symbol in the bitstream. */
-	template<class BITSTREAM>
-	uint32 getSymbol(BITSTREAM &bits) const {
-		uint32 code = 0;
-
-		for (uint32 i = 0; i < _codes.size(); i++) {
-			bits.addBit(code, i);
-
-			for (CodeList::const_iterator cCode = _codes[i].begin(); cCode != _codes[i].end(); ++cCode)
-				if (code == cCode->code)
-					return cCode->symbol;
-		}
-
-		error("Unknown Huffman code");
-		return 0;
-	}
+	uint32 getSymbol(BITSTREAM &bits) const;
 
 private:
 	struct Symbol {
 		uint32 code;
 		uint32 symbol;
 
-		Symbol(uint32 c, uint32 s);
+		Symbol(uint32 c, uint32 s) : code(c), symbol(s) {}
 	};
 
 	typedef List<Symbol> CodeList;
 	typedef Array<CodeList> CodeLists;
-	typedef Array<Symbol *> SymbolList;
 
 	/** Lists of codes and their symbols, sorted by code length. */
 	CodeLists _codes;
 
-	/** Sorted list of pointers to the symbols. */
-	SymbolList _symbols;
+	/** Prefix lookup table used to speed up the decoding of short codes. */
+	struct PrefixEntry {
+		uint32 symbol;
+		uint8  length;
+
+		PrefixEntry() : length(0xFF) {}
+	};
+
+	static const uint8 _prefixTableBits = 8;
+	PrefixEntry _prefixTable[1 << _prefixTableBits];
 };
 
+template <class BITSTREAM>
+Huffman<BITSTREAM>::Huffman(uint8 maxLength, uint32 codeCount, const uint32 *codes, const uint8 *lengths, const uint32 *symbols) {
+	assert(codeCount > 0);
+
+	assert(codes);
+	assert(lengths);
+
+	if (maxLength == 0)
+		for (uint32 i = 0; i < codeCount; i++)
+			maxLength = MAX(maxLength, lengths[i]);
+
+	assert(maxLength <= 32);
+
+	// Codes that don't fit in the prefix table are stored in the _codes array
+	_codes.resize(MAX(maxLength - _prefixTableBits, 0));
+
+	for (uint i = 0; i < codeCount; i++) {
+		uint8 length = lengths[i];
+
+		// The symbol. If none were specified, just assume it's identical to the code index
+		uint32 symbol = symbols ? symbols[i] : i;
+
+		if (length <= _prefixTableBits) {
+			// Short codes go in the prefix lookup table. Set all the entries in the table
+			// with an index starting with the code to the symbol value.
+			uint32 startIndex;
+			if (BITSTREAM::isMSB2LSB()) {
+				startIndex = codes[i] << (_prefixTableBits - length);
+			} else {
+				startIndex = REVERSEBITS(codes[i]) >> (32 - _prefixTableBits);
+			}
+
+			uint32 endIndex = startIndex | ((1 << (_prefixTableBits - length)) - 1);
+
+			for (uint32 j = startIndex; j <= endIndex; j++) {
+				uint32 index = BITSTREAM::isMSB2LSB() ? j : REVERSEBITS(j) >> (32 - _prefixTableBits);
+				_prefixTable[index].symbol = symbol;
+				_prefixTable[index].length = length;
+			}
+		} else {
+			// Put the code and symbol into the correct list for the length
+			_codes[lengths[i] - 1 - _prefixTableBits].push_back(Symbol(codes[i], symbol));
+		}
+	}
+}
+
+template <class BITSTREAM>
+uint32 Huffman<BITSTREAM>::getSymbol(BITSTREAM &bits) const {
+	uint32 code = bits.peekBits(_prefixTableBits);
+
+	uint8 length = _prefixTable[code].length;
+
+	if (length != 0xFF) {
+		bits.skip(length);
+		return _prefixTable[code].symbol;
+	} else {
+		bits.skip(_prefixTableBits);
+
+		for (uint32 i = 0; i < _codes.size(); i++) {
+			bits.addBit(code, i + _prefixTableBits);
+
+			for (typename CodeList::const_iterator cCode = _codes[i].begin(); cCode != _codes[i].end(); ++cCode)
+				if (code == cCode->code)
+					return cCode->symbol;
+		}
+	}
+
+	error("Unknown Huffman code");
+	return 0;
+}
+
 } // End of namespace Common
 
 #endif // COMMON_HUFFMAN_H