COMMON: Use a prefix table to speed up the Huffman decoder

Symbols for codes shorter than the prefix table index width are stored
in the table. All the entries in the table with an index starting with
the code are set to the symbol value. That way, when decoding it is
possible to get the number of bits corresponding to the table width from
the bitstream and directly find the symbol value. Longer code still need
to be searched for in the codes list.

1 files changed, 5 insertions, 2 deletions

diff --git a/video/psx_decoder.h b/video/psx_decoder.h
index c96642276a..183b6da317 100644
--- a/video/psx_decoder.h
+++ b/video/psx_decoder.h
@@ -36,6 +36,7 @@ class QueuingAudioStream;
 }
 
 namespace Common {
+template <class BITSTREAM>
 class Huffman;
 }
 
@@ -105,16 +106,18 @@ private:
 			kPlaneV = 2
 		};
 
+		typedef Common::Huffman<Common::BitStreamMemory16LEMSB> HuffmanDecoder;
+
 		uint16 _macroBlocksW, _macroBlocksH;
 		byte *_yBuffer, *_cbBuffer, *_crBuffer;
 		void decodeMacroBlock(Common::BitStreamMemory16LEMSB *bits, int mbX, int mbY, uint16 scale, uint16 version);
 		void decodeBlock(Common::BitStreamMemory16LEMSB *bits, byte *block, int pitch, uint16 scale, uint16 version, PlaneType plane);
 
 		void readAC(Common::BitStreamMemory16LEMSB *bits, int *block);
-		Common::Huffman *_acHuffman;
+		HuffmanDecoder *_acHuffman;
 
 		int readDC(Common::BitStreamMemory16LEMSB *bits, uint16 version, PlaneType plane);
-		Common::Huffman *_dcHuffmanLuma, *_dcHuffmanChroma;
+		HuffmanDecoder *_dcHuffmanLuma, *_dcHuffmanChroma;
 		int _lastDC[3];
 
 		void dequantizeBlock(int *coefficients, float *block, uint16 scale);