Function lodepng_zlib_decompress

dependency/densecrf/examples/lodepng.cpp:2126–2169

#ifdef LODEPNG_COMPILE_DECODER

unsigned lodepng_zlib_decompress(unsigned char** out, size_t* outsize, const unsigned char* in,
                                 size_t insize, const LodePNGDecompressSettings* settings)
{
    unsigned error = 0;
    unsigned CM, CINFO, FDICT;
    
    if(insize < 2) return 53; /*error, size of zlib data too small*/
    /*read information from zlib header*/
    if((in[0] * 256 + in[1]) % 31 != 0)
    {
        /*error: 256 * in[0] + in[1] must be a multiple of 31, the FCHECK value is supposed to be made that way*/
        return 24;
    }
    
    CM = in[0] & 15;
    CINFO = (in[0] >> 4) & 15;
    /*FCHECK = in[1] & 31;*/ /*FCHECK is already tested above*/
    FDICT = (in[1] >> 5) & 1;
    /*FLEVEL = (in[1] >> 6) & 3;*/ /*FLEVEL is not used here*/
    
    if(CM != 8 || CINFO > 7)
    {
        /*error: only compression method 8: inflate with sliding window of 32k is supported by the PNG spec*/
        return 25;
    }
    if(FDICT != 0)
    {
        /*error: the specification of PNG says about the zlib stream:
         "The additional flags shall not specify a preset dictionary."*/
        return 26;
    }
    
    error = inflate(out, outsize, in + 2, insize - 2, settings);
    if(error) return error;
    
    if(!settings->ignore_adler32)
    {
        unsigned ADLER32 = lodepng_read32bitInt(&in[insize - 4]);
        unsigned checksum = adler32(*out, (unsigned)(*outsize));
        if(checksum != ADLER32) return 58; /*error, adler checksum not correct, data must be corrupted*/
    }
    
    return 0; /*no error*/
}

static unsigned zlib_decompress(unsigned char** out, size_t* outsize, const unsigned char* in,
                                size_t insize, const LodePNGDecompressSettings* settings)