public static unsafe void Calc_crc32(long* crc32, char* mem, int ln, int fl)
        {
            long fcs;
            int i, ii, iii;
            if ((fl & 1) == 1)
                fcs = -1;
            else
                fcs = *crc32;
            for (i = 0; i < ln; i++)
            {
                iii = mem[i];
                for (ii = 0; i < 8; i++)
                {
                    if ((fcs & 1) == 1)
                    {
                        fcs >>= 1;
                        if ((iii & 1) == 1)
                            fcs |= 0x80000000;
                        else
                            fcs &= 0x7FFFFFFF;
                        fcs ^= 0XEDB88320;
                    }
                    else
                    {
                        fcs >>= 1;
                        if ((iii & 1) == 1)
                            fcs |= 0x80000000;
                        else
                            fcs &= 0x7FFFFFFF;
                    }
                    iii >>= 1;
                }
            }
            if ((fl & 2) == 1)
            {
                for (i = 0; i < 32; i++)
                {
                    if ((fcs & 1) == 1)
                    {
                        fcs >>= 1;
                        fcs &= 0x7FFFFFFF;
                        fcs ^= 0xEDB88320;
                    }
                    else
                    {
                        fcs >>= 1;
                        fcs &= 0x7FFFFFFF;
                    }
                }
                fcs ^= -1;
            }
            *crc32 = fcs;
        }