compression.h

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/* (c) Magnus Auvinen. See licence.txt in the root of the distribution for more information. */
/* If you are missing that file, acquire a complete release at teeworlds.com.                */
#ifndef ENGINE_SHARED_COMPRESSION_H
#define ENGINE_SHARED_COMPRESSION_H
 
// variable int packing
class CVariableInt
{
public:
    enum
    {
        MAX_BYTES_PACKED = 5, // maximum number of bytes in a packed int
    };
 
    // Format: ESDDDDDD EDDDDDDD EDD... Extended, Data, Sign
    // Defined here so that callers packing many ints in a row do not pay a call per int.
    static unsigned char *Pack(unsigned char *pDst, int i, int DstSize)
    {
        if(DstSize <= 0)
            return nullptr;
 
        DstSize--;
        *pDst = 0;
        if(i < 0)
        {
            *pDst |= 0x40; // set sign bit
            i = ~i;
        }
 
        *pDst |= i & 0x3F; // pack 6bit into dst
        i >>= 6; // discard 6 bits
        while(i)
        {
            if(DstSize <= 0)
                return nullptr;
            *pDst |= 0x80; // set extend bit
            DstSize--;
            pDst++;
            *pDst = i & 0x7F; // pack 7bit
            i >>= 7; // discard 7 bits
        }
 
        pDst++;
        return pDst;
    }
 
    static const unsigned char *Unpack(const unsigned char *pSrc, int *pInOut, int SrcSize);
 
    static long Compress(const void *pSrc, int SrcSize, void *pDst, int DstSize);
    static long Decompress(const void *pSrc, int SrcSize, void *pDst, int DstSize);
};
 
#endif