Use the upstream version of libwebp, v0.4.3.

third_party/libwebp/utils/huffman_encode.h

+// Copyright 2011 Google Inc. All Rights Reserved.
+//
+// Use of this source code is governed by a BSD-style license
+// that can be found in the COPYING file in the root of the source
+// tree. An additional intellectual property rights grant can be found
+// in the file PATENTS. All contributing project authors may
+// be found in the AUTHORS file in the root of the source tree.
+// -----------------------------------------------------------------------------
+//
+// Author: Jyrki Alakuijala (jyrki@google.com)
+//
+// Entropy encoding (Huffman) for webp lossless
+
+#ifndef WEBP_UTILS_HUFFMAN_ENCODE_H_
+#define WEBP_UTILS_HUFFMAN_ENCODE_H_
+
+#include "../webp/types.h"
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+// Struct for holding the tree header in coded form.
+typedef struct {
+  uint8_t code;         // value (0..15) or escape code (16,17,18)
+  uint8_t extra_bits;   // extra bits for escape codes
+} HuffmanTreeToken;
+
+// Struct to represent the tree codes (depth and bits array).
+typedef struct {
+  int       num_symbols;   // Number of symbols.
+  uint8_t*  code_lengths;  // Code lengths of the symbols.
+  uint16_t* codes;         // Symbol Codes.
+} HuffmanTreeCode;
+
+// Struct to represent the Huffman tree.
+// TODO(vikasa): Add comment for the fields of the Struct.
+typedef struct {
+  uint32_t total_count_;
+  int value_;
+  int pool_index_left_;    // Index for the left sub-tree.
+  int pool_index_right_;   // Index for the right sub-tree.
+} HuffmanTree;
+
+// Turn the Huffman tree into a token sequence.
+// Returns the number of tokens used.
+int VP8LCreateCompressedHuffmanTree(const HuffmanTreeCode* const tree,
+                                    HuffmanTreeToken* tokens, int max_tokens);
+
+// Create an optimized tree, and tokenize it.
+// 'buf_rle' and 'huff_tree' are pre-allocated and the 'tree' is the constructed
+// huffman code tree.
+void VP8LCreateHuffmanTree(uint32_t* const histogram, int tree_depth_limit,
+                           uint8_t* const buf_rle, HuffmanTree* const huff_tree,
+                           HuffmanTreeCode* const tree);
+
+#ifdef __cplusplus
+}
+#endif
+
+#endif  // WEBP_UTILS_HUFFMAN_ENCODE_H_