Return the checksum of the buffer

   
 

// crudwork
// Copyright 2004 by Steve T. Pham (http://www.crudwork.com)
//
// This program is free software: you can redistribute it and/or modify
// it under the terms of the GNU General Public License as published by
// the Free Software Foundation, either version 3 of the License, or
// (at your option) any later version.
//
// This program is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
// GNU General Public License for more details.
//
// You should have received a copy of the GNU General Public License
// along with This program.  If not, see <http://www.gnu.org/licenses/>.

using System;
using System.Collections.Generic;
using System.Text;
using System.IO;

namespace crudwork.Utilities
{
  /// <summary>
  /// Math Utility
  /// </summary>
  public static class MathUtil
  {
    /// <summary>
    /// Return the checksum of the buffer
    /// </summary>
    /// <param name="buffer"></param>
    /// <returns></returns>
    public static long ComputeChecksum(byte[] buffer)
    {
      return ComputeChecksum(buffer, 0);
    }

    /// <summary>
    /// Return the checksum of the buffer at the given offset
    /// </summary>
    /// <param name="buffer"></param>
    /// <param name="offset"></param>
    /// <returns></returns>
    public static long ComputeChecksum(byte[] buffer, int offset)
    {
      long sum = 0;
      for (int i = 0; i < buffer.Length; i++)
      {
        sum += buffer&#91;i&#93; * (i + 1 + offset);
      }
      return sum;
    }

    /// <summary>
    /// Return the checksum value of the given filename
    /// </summary>
    /// <param name="filename"></param>
    /// <returns></returns>
    public static long ComputeChecksum(string filename)
    {
      //byte[] buffer = FileUtil.ReadFile(filename, 4096);
      //return ComputeChecksum(buffer);

      long sum = 0;
      int bufSize = 4096;

      using (FileStream fs = new FileStream(filename, FileMode.Open, FileAccess.Read))
      using (BinaryReader r = new BinaryReader(fs))
      {
        byte[] readChar = null;
        int offset = 0;
        
        do
        {
          readChar = r.ReadBytes(bufSize);
          sum += ComputeChecksum(readChar, offset);
          offset += readChar.Length;
        } while ((readChar != null) &amp;&amp; (readChar.Length > 0));

        r.Close();
        //fs.Close();
      }

      return sum;
    }
  }
}