std::vector<unsigned char> Compressor::compress(void* data, unsigned length)
{
mFrequency = getFrequency(data, length);
int bits = getBestRatio(length);
char* ptr = (char*)data;
int i;
if (bits == -1)
return std::vector<unsigned char>();
BitStream bs;
unsigned totalSize = 27 + ((1 << bits) - 1) * 8;
if (mIsLittleEndian)
bs.insert((int)length, 24);
else
bs.insert(reverseEndianess((int)length), 24);
bs.insert(bits, 3);
for (i = 0; i < (1 << bits) - 1; i++)
{
if ((int)mFrequency.size() > i)
bs.insert(mFrequency[i].character);
else
bs.insert(0);
}
std::vector<char> uncompressed;
for (i = 0; i < (int)length; i++)
{
int vecPos = findChar(mFrequency, *ptr, (1 << bits) - 1);
if (vecPos == -1)
{
bs.insert(0U, bits);
uncompressed.push_back(*ptr);
}
else
{
bs.insert(vecPos + 1, bits);
}
totalSize += bits;
ptr++;
}
for (i = 0; i < (int)uncompressed.size(); i++)
{
bs.insert(uncompressed[i]);
totalSize += 8;
}
return bs.getData();
}
std::vector<unsigned char> Compressor::decompress(void* data, unsigned length)
{
BitStream bs;
bs.insert(data, length);
bs.read_bytes(&length, 3);
if (!mIsLittleEndian)
length = (unsigned)reverseEndianess((int)length);
unsigned char bits;
bs.read_bits(bits, 3);
if (bits < 1 || bits > 7)
{
char bStr[4];
throw (std::string("Bit-size of enconding isn't valid: ") + std::string(itoa(bits, bStr, 10)));
}
unsigned char byte;
int bitsRead = 27;
int i;
std::vector<char> charTable;
std::vector<char> compressedChars;
for (i = 1; i <= (1 << bits) - 1; i++)
{
bs.read_bits(byte, 8);
charTable.push_back(byte);
bitsRead += 8;
if (!bs.canRead())
throw std::string ("Bad file for decompression [1]");
}
for (unsigned j = 1; j <= length; j++)
{
bs.read_bits(byte, bits);
bitsRead += bits;
compressedChars.push_back(byte);
if (!bs.canRead())
throw std::string ("Bad file for decompression [2]");
}
std::vector<unsigned char> result(length, 0);
for (i = 0; i < (int)compressedChars.size(); i++)
{
if (compressedChars[i] == 0 || (unsigned char)compressedChars[i] > charTable.size())
{
if (!bs.canRead())
throw std::string ("Bad file for decompression [3]");
bs.read_bits(result[i], 8);
bitsRead += 8;
}
else
{
result[i] = charTable[compressedChars[i] - 1];
}
}
return result;
}