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Updates to Brotli compression format, decoder and encoder

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This commit contains a batch of changes that were made to the Brotli
compression algorithm in the last month. Most important changes:

   * Updated spec
   * Changed Huffman code length alphabet to use run length codes more
     efficiently, based on a suggestion by Robert Obryk
   * Changed encoding of the number of Huffman code lengths (HLEN)
   * Changed encoding of the number of Huffman trees (NTREES)
   * Added support for uncompressed meta-blocks
This commit is contained in:
Zoltan Szabadka
2013-12-12 13:18:04 +01:00
parent fe79fac8da
commit e70949119a
11 changed files with 411 additions and 263 deletions
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brotli/enc/entropy_encode.h
+5 -1
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@@ -98,7 +98,7 @@ void BuildEntropyCode(const Histogram<kSize>& histogram,
ConvertBitDepthsToSymbols(&code->depth_[0], alphabet_size, &code->bits_[0]);
}
static const int kCodeLengthCodes = 19;
static const int kCodeLengthCodes = 18;
// Literal entropy code.
typedef EntropyCode<256> EntropyCodeLiteral;
@@ -106,6 +106,10 @@ typedef EntropyCode<256> EntropyCodeLiteral;
typedef EntropyCode<kNumCommandPrefixes> EntropyCodeCommand;
typedef EntropyCode<kNumDistancePrefixes> EntropyCodeDistance;
typedef EntropyCode<kNumBlockLenPrefixes> EntropyCodeBlockLength;
// Context map entropy code, 256 Huffman tree indexes + 16 run length codes.
typedef EntropyCode<272> EntropyCodeContextMap;
// Block type entropy code, 256 block types + 2 special symbols.
typedef EntropyCode<258> EntropyCodeBlockType;
} // namespace brotli