LZW/header2.h at master · 17robots/LZW · GitHub

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#include <string>
#include <map>
#include <iostream>
#include <fstream>
#include <iterator>
#include <cmath>
#include <vector>
#include <set>
#include <sys/stat.h>

template <typename Iterator>
Iterator compress(const std::string &uncompressed, Iterator result)
{
  // Build the dictionary.
  int dictSize = 256;
  int bits = 9;
  std::map<std::string, int> dictionary;
  for (int i = 0; i < 256; i++)
    dictionary[std::string(1, i)] = i;

  std::string w;
  for (std::string::const_iterator it = uncompressed.begin();
       it != uncompressed.end(); ++it)
  {
    char c = *it;
    std::string wc = w + c;
    if (dictionary.count(wc))
      w = wc;
    else
    {
      *result++ = dictionary[w];
      if (dictionary.size() < pow(2, bits))
        dictionary[wc] = dictSize++;
      else
      {
        if (bits < 16)
        {
          bits++;
          dictionary[wc] = dictSize++;
        }
      }
      // log2 << dictSize - 1 << ": " << wc << '\n';
      w = std::string(1, c);
    }
  }
  // Output the code for w.
  if (!w.empty())
    *result++ = dictionary[w];
  return result;
}

int binaryString2Int(std::string p);

// template <typename Iterator>
std::string decompress(std::string &s) {
  // Build the dictionary.
  int dictSize = 256;
  int bits = 9;
  std::map<int,std::string> dictionary;
  for (int i = 0; i < 256; i++)
    dictionary[i] = std::string(1, i);

  std::string w(1, binaryString2Int(s.substr(0, bits)));
  std::string result = w;
  std::string entry;
  int max = pow(2, bits);
  for (int j = bits; j < s.size(); ++j) {
    if(s.size() - j < bits) break;
    int k = binaryString2Int(s.substr(j, bits));
    // std::cout << "K " << k << '\n';
    if (dictionary.count(k))
      entry = dictionary[k];
    else if (k >= dictSize)
      entry = w + w[0];
    else
      throw "Bad compressed k";

    result += entry;

    // Add w+entry[0] to the dictionary.
    if (dictionary.size()<max)
      dictionary[dictSize++] = w + entry[0];
    else {
      if(bits < 16) {
        bits++;
        max = pow(2, bits);
        dictionary[dictSize++] = w + entry[0];
      }
    }
    w = entry;
  }
  return result;
}

std::string int2BinaryString(int c, int cl)
{
  std::string p = ""; //a binary code string with code length = cl
  int code = c;
  while (c > 0)
  {
    if (c % 2 == 0)
      p = "0" + p;
    else
      p = "1" + p;
    c = c >> 1;
  }
  int zeros = cl - p.size();
  if (zeros < 0)
  {
    std::cout << "\nWarning: Overflow. code " << code << " is too big to be coded by " << cl << " bits!\n";
    p = p.substr(p.size() - cl);
  }
  else
  {
    for (int i = 0; i < zeros; i++) //pad 0s to left of the binary code if needed
      p = "0" + p;
  }
  return p;
}

int binaryString2Int(std::string p)
{
  int code = 0;
  if (p.size() > 0)
  {
    if (p.at(0) == '1')
      code = 1;
    p = p.substr(1);
    while (p.size() > 0)
    {
      code = code << 1;
      if (p.at(0) == '1')
        code++;
      p = p.substr(1);
    }
  }
  return code;
}