Is it possible to do CRC-32 calculation in splits?

Question

I use this trivial function to calculate the CRC checksum of a given file:

long i, j = 0;
int k = 0;
uint crc = 0xFFFFFFFF;
FileInfo file_info = new FileInfo(fil         


        

Answer 1

I know this is an old question but this is what I use for "chunking" CRC calculations in case this helps anyone:

public static class Crc32Checksum
{
    private static readonly uint[] Table = GenerateTable();

    /// 

    /// Calculates a CRC32 value for the data given.
    /// 
    /// Data contents
    /// Byte offset to start reading
    /// Number of bytes to read
    /// The computed CRC32 value.
    public static int Calculate(byte[] data, int offset, int count) 
        => Calculate(0, data, offset, count);

    /// 

    /// Calculates a new CRC32 value given additional data for the current CRC value.
    /// 
    /// The current CRC value to start with
    /// Additional data contents
    /// Byte offset to start reading
    /// Number of bytes to read
    /// The computed CRC32 value.
    public static int Calculate(int currentCrc, byte[] data, int offset, int count)
    {
        unchecked
        {
            uint crc = ~(uint)currentCrc;

            for (int i = offset, end = offset + count; i < end; i++)
                crc = (crc >> 8) ^ Table[(crc ^ data[i]) & 0xFF];

            return (int)~crc;
        }
    }

    private static uint[] GenerateTable()
    {
        unchecked
        {
            var table = new uint[256];

            const uint poly = 0xEDB88320;

            for (uint i = 0; i < table.Length; i++)
            {
                uint crc = i;

                for (int j = 8; j > 0; j--)
                {
                    if ((crc & 1) == 1)
                        crc = (crc >> 1) ^ poly;
                    else
                        crc >>= 1;
                }

                table[i] = crc;
            }

            return table;
        }
    }
}