DataCompressor.cpp

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#include "DataCompressor.h"
#include "DS_HuffmanEncodingTree.h"
#include "RakAssert.h"
#include <string.h> // Use string.h rather than memory.h for a console

void DataCompressor::Compress( unsigned char *userData, unsigned sizeInBytes, RakNet::BitStream * output )
{
        // Don't use this for small files as you will just make them bigger!
        RakAssert(sizeInBytes > 2048);

        unsigned int frequencyTable[ 256 ];
        unsigned int i;
        memset(frequencyTable,0,256*sizeof(unsigned int));
        for (i=0; i < sizeInBytes; i++)
                ++frequencyTable[userData[i]];
        HuffmanEncodingTree tree;
        BitSize_t writeOffset1, writeOffset2, bitsUsed1, bitsUsed2;
        tree.GenerateFromFrequencyTable(frequencyTable);
        output->WriteCompressed(sizeInBytes);
        for (i=0; i < 256; i++)
                output->WriteCompressed(frequencyTable[i]);
        output->AlignWriteToByteBoundary();
        writeOffset1=output->GetWriteOffset();
        output->Write((unsigned int)0); // Dummy value
        bitsUsed1=output->GetNumberOfBitsUsed();
        tree.EncodeArray(userData, sizeInBytes, output);
        bitsUsed2=output->GetNumberOfBitsUsed();
        writeOffset2=output->GetWriteOffset();
        output->SetWriteOffset(writeOffset1);
        output->Write(bitsUsed2-bitsUsed1); // Go back and write how many bits were used for the encoding
        output->SetWriteOffset(writeOffset2);
}

unsigned DataCompressor::DecompressAndAllocate( RakNet::BitStream * input, unsigned char **output )
{
        HuffmanEncodingTree tree;
        unsigned int bitsUsed, destinationSizeInBytes;
        unsigned int decompressedBytes;
        unsigned int frequencyTable[ 256 ];
        unsigned i;
        
        input->ReadCompressed(destinationSizeInBytes);
        for (i=0; i < 256; i++)
                input->ReadCompressed(frequencyTable[i]);
        input->AlignReadToByteBoundary();
        if (input->Read(bitsUsed)==false)
        {
                // Read error
#ifdef _DEBUG
                RakAssert(0);
#endif
                return 0;
        }
        *output = (unsigned char*) rakMalloc_Ex(destinationSizeInBytes, __FILE__, __LINE__);
        tree.GenerateFromFrequencyTable(frequencyTable);
        decompressedBytes=tree.DecodeArray(input, bitsUsed, destinationSizeInBytes, *output );
        RakAssert(decompressedBytes==destinationSizeInBytes);
        return destinationSizeInBytes;
}