[DRAFT][onert-micro] Introduce Huffman Transcoder

onert-micro/onert-micro/include/core/OMHuffmanTranscoder.h

@@ -0,0 +1,177 @@
+/*
+ * Copyright (c) 2024 Samsung Electronics Co., Ltd. All Rights Reserved
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *    http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#ifndef ONERT_MICRO_CORE_OM_HUFFMAN_TRANSCODER_H
+#define ONERT_MICRO_CORE_OM_HUFFMAN_TRANSCODER_H
+#include <iostream>
+#include <unordered_map>
+#include <vector>
+#include <tuple>
+#include <queue>
+#include <string>
+#include <climits>
+namespace onert_micro
+{
+namespace core
+{
+template <typename T> struct Node
+{
+  Node *p_left = nullptr;
+  Node *p_right = nullptr;
+  T data;
+  unsigned int freq;
+};
+
+template <typename T> struct CompareNodes
+{
+  bool operator()(Node<T> *l, Node<T> *r) { return l->freq > r->freq; }
+};
+
+template <typename T> class HuffmanTranscoder
+{
+private:
+  Node<T> *root = nullptr;
+  std::unordered_map<T, std::string> huffmanCode;
+  std::vector<bool> encoded_bitset{};
+  std::size_t nodes_count = 0;
+
+private:
+  Node<T> *allocateNode(T data, unsigned int freq, Node<T> *p_left, Node<T> *p_right)
+  {
+    Node<T> *node = new Node<T>;
+    node->data = data;
+    node->freq = freq;
+    node->p_left = p_left;
+    node->p_right = p_right;
+    nodes_count++;
+    return node;
+  }
+  std::unordered_map<T, unsigned int> calculate_frequency_map(const std::vector<T> &input)
+  {
+    std::unordered_map<T, unsigned int> out_map;
+    for (auto &item : input)
+      out_map[item] = out_map.find(item) != out_map.end() ? out_map[item] + 1 : 1;
+    return out_map;
+  }
+
+  void buildHuffmanTable(Node<T> *node, const std::string str)
+  {
+    if (node == nullptr)
+      return;
+
+    if (!node->p_left && !node->p_right)
+    {
+      huffmanCode[node->data] = str;
+    }
+
+    buildHuffmanTable(node->p_left, str + "0");
+    buildHuffmanTable(node->p_right, str + "1");
+  }
+  void decode(Node<T> *node, int &index, std::string str)
+  {
+    if (node == nullptr)
+    {
+      return;
+    }
+
+    if (!node->p_left && !node->p_right)
+    {
+      std::cout << static_cast<int>(node->data);
+      return;
+    }
+
+    index++;
+
+    if (str[index] == '0')
+      decode(node->p_left, index, str);
+    else
+      decode(node->p_right, index, str);
+  }
+  void buildHuffmanTree(const std::vector<T> &input)
+  {
+    auto freq_map = calculate_frequency_map(input);
+
+    std::priority_queue<Node<T> *, std::vector<Node<T> *>, CompareNodes<T>> pq;
+
+    for (auto &item : freq_map)
+    {
+      pq.push(allocateNode(item.first, item.second, nullptr, nullptr));
+    }
+
+    while (pq.size() != 1)
+    {
+      Node<T> *left = pq.top();
+      pq.pop();
+      Node<T> *right = pq.top();
+      pq.pop();
+
+      unsigned int sum = left->freq + right->freq;
+      pq.push(allocateNode(0, sum, left, right));
+    }
+
+    root = pq.top();
+  }
+
+public:
+  void encode_decode_example()
+  {
+
+    std::vector<T> input;
+    for (int i = 0; i < 1024; ++i)
+      input.push_back(0);
+    for (int i = 0; i < 256; ++i)
+      input.push_back(i);
+
+    buildHuffmanTree(input);
+    buildHuffmanTable(root, "");
+
+    // std::cout << "Huffman Codes are :\n";
+    // for (auto pair : huffmanCode) {
+    //	std::cout << static_cast<int>(pair.first) << " " << pair.second << '\n';
+    // }
+
+    std::cout << "\nInput string bits:\n";
+    auto input_bits = input.size() * CHAR_BIT * sizeof(T);
+    std::cout << input_bits << "\n";
+
+    // TODO: replace string with bitset or bool vector
+    // print encoded string
+    std::string str = "";
+    for (auto &item : input)
+    {
+      str += huffmanCode[item];
+    }
+
+    // std::cout << "\nEncoded string is :\n" << str << '\n';
+    std::cout << "\nEncoded string bits:\n" << str.size() << '\n';
+    auto tree_bits = nodes_count + CHAR_BIT * sizeof(T) * huffmanCode.size();
+    std::cout << "Bits to store tree:\n" << tree_bits << '\n';
+    auto encoded_bits_total = tree_bits + str.size();
+    std::cout << "Compression:\n"
+              << ((input_bits - encoded_bits_total) / (float)input_bits) * 100 << "% \n";
+
+    // decode the encoded string
+    // int index = -1;
+    // std::cout << "\nDecoded string is: \n";
+    // while (index < (int)str.size() - 2) {
+    //	decode(root, index, str);
+    //}
+  }
+  HuffmanTranscoder() = default;
+};
+} // namespace core
+} // namespace onert_micro
+#endif // ONERT_MICRO_CORE_OM_HUFFMAN_TRANSCODER_H