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+// Copyright 2012 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.
+// -----------------------------------------------------------------------------
+//
+// Utilities for building and looking up Huffman trees.
+//
+// Author: Urvang Joshi (urvang@google.com)
+
+#ifndef WEBP_UTILS_HUFFMAN_H_
+#define WEBP_UTILS_HUFFMAN_H_
+
+#include <assert.h>
+#include "../webp/types.h"
+
+#ifdef __cplusplus
+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;
+
+// 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 WEBP_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 WEBP_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 HuffmanTreeRelease(HuffmanTree* const tree);
+
+// Builds Huffman tree assuming code lengths are implicitly in symbol order.
+// Returns false in case of error (invalid tree or memory error).
+int HuffmanTreeBuildImplicit(HuffmanTree* const tree,
+                             const int* const code_lengths,
+                             int code_lengths_size);
+
+// Build a Huffman tree with explicitly given lists of code lengths, codes
+// and symbols. Verifies that all symbols added are smaller than max_symbol.
+// Returns false in case of an invalid symbol, invalid tree or memory error.
+int HuffmanTreeBuildExplicit(HuffmanTree* const tree,
+                             const int* const code_lengths,
+                             const int* const codes,
+                             const int* const symbols, int max_symbol,
+                             int num_symbols);
+
+// Utility: converts Huffman code lengths to corresponding Huffman codes.
+// 'huff_codes' should be pre-allocated.
+// Returns false in case of error (memory allocation, invalid codes).
+int HuffmanCodeLengthsToCodes(const int* const code_lengths,
+                              int code_lengths_size, int* const huff_codes);
+
+
+#ifdef __cplusplus
+}    // extern "C"
+#endif
+
+#endif  // WEBP_UTILS_HUFFMAN_H_