add utils/huffman.[hc] from experimental

Pulled from the current HEAD (218c32e).
The history of this and related files is a bit entangled so rather
trying to split the changes and introduce some noise in master's history
we'll start with a fresh snapshot.
The file progression is still available in the experimental branch.

Change-Id: Ie57be21bf50ad83808c72aeb5fc706d9954d01d8

src/utils/huffman.h

@@ -0,0 +1,79 @@
+// Copyright 2012 Google Inc. All Rights Reserved.
+//
+// This code is licensed under the same terms as WebM:
+//  Software License Agreement:  http://www.webmproject.org/license/software/
+//  Additional IP Rights Grant:  http://www.webmproject.org/license/additional/
+// -----------------------------------------------------------------------------
+//
+// A utility for building and reading looking up trees for Huffman coding.
+//
+// Author: urvang@google.com (Urvang Joshi)
+
+#ifndef WEBP_UTILS_HUFFMAN_H_
+#define WEBP_UTILS_HUFFMAN_H_
+
+#include <assert.h>
+#include <stddef.h>
+#include "../webp/types.h"
+
+#if defined(__cplusplus) || defined(c_plusplus)
+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.
+typedef struct HuffmanTree HuffmanTree;
+struct HuffmanTree {
+  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 a leaf of the Huffman tree.
+static WEBP_INLINE int HuffmanTreeNodeIsLeaf(
+    const HuffmanTreeNode* const node) {
+  return (node->children_ == 0);
+}
+
+// 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.
+// Returns false in case of error (invalid tree or memory error).
+int HuffmanTreeBuildExplicit(HuffmanTree* const tree,
+                             const int* const code_lengths,
+                             const int* const codes,
+                             const int* const symbols,
+                             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);
+
+
+#if defined(__cplusplus) || defined(c_plusplus)
+}    // extern "C"
+#endif
+
+#endif  // WEBP_UTILS_HUFFMAN_H_