Updates to Brotli compression format, decoder and encoder

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

   * Fixes to the spec.
   * Change of code length code order.
   * Use a 2-level Huffman lookup table in the decoder.
   * Faster uncompressed meta-block decoding.
   * Optimized encoding of the Huffman code.
   * Detection of UTF-8 input encoding.
   * UTF-8 based literal cost modeling for improved
     backward reference selection.

brotli/dec/huffman.h

@@ -12,7 +12,7 @@
    See the License for the specific language governing permissions and
    limitations under the License.
 
-   Utilities for building and looking up Huffman trees.
+   Utilities for building Huffman decoding tables.
 */
 
 #ifndef BROTLI_DEC_HUFFMAN_H_
@@ -25,48 +25,17 @@
 extern "C" {
 #endif
 
-/* A node of a Huffman tree. */
 typedef struct {
-  int symbol_;
-  int children_;  /* delta offset to both children (contiguous) or 0 if leaf. */
-} HuffmanTreeNode;
+  uint8_t bits;     /* number of bits used for this symbol */
+  uint16_t value;   /* symbol value or table offset */
+} HuffmanCode;
 
-/* Huffman Tree. */
-#define HUFF_LUT_BITS 7
-#define HUFF_LUT (1U << HUFF_LUT_BITS)
-typedef struct HuffmanTree HuffmanTree;
-struct HuffmanTree {
-  /* Fast lookup for short bit lengths. */
-  uint8_t lut_bits_[HUFF_LUT];
-  int16_t lut_symbol_[HUFF_LUT];
-  int16_t lut_jump_[HUFF_LUT];
-  /* Complete tree for lookups. */
-  HuffmanTreeNode* root_;   /* all the nodes, starting at root. */
-  int max_nodes_;           /* max number of nodes */
-  int num_nodes_;           /* number of currently occupied nodes */
-};
-
-/* Returns true if the given node is not a leaf of the Huffman tree. */
-static BROTLI_INLINE int HuffmanTreeNodeIsNotLeaf(
-    const HuffmanTreeNode* const node) {
-  return node->children_;
-}
-
-/* Go down one level. Most critical function. 'right_child' must be 0 or 1. */
-static BROTLI_INLINE const HuffmanTreeNode* HuffmanTreeNextNode(
-    const HuffmanTreeNode* node, int right_child) {
-  return node + node->children_ + right_child;
-}
-
-/* Releases the nodes of the Huffman tree. */
-/* Note: It does NOT free 'tree' itself. */
-void BrotliHuffmanTreeRelease(HuffmanTree* const tree);
-
-/* Builds Huffman tree assuming code lengths are implicitly in symbol order. */
+/* Builds Huffman lookup table assuming code lengths are in symbol order. */
 /* Returns false in case of error (invalid tree or memory error). */
-int BrotliHuffmanTreeBuildImplicit(HuffmanTree* const tree,
-                                   const uint8_t* const code_lengths,
-                                   int code_lengths_size);
+int BrotliBuildHuffmanTable(HuffmanCode* root_table,
+                            int root_bits,
+                            const uint8_t* const code_lengths,
+                            int code_lengths_size);
 
 #if defined(__cplusplus) || defined(c_plusplus)
 }    /* extern "C" */