{filelink=17829}

// 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 .

using System;
using System.Text;
using System.IO;

namespace MesExemples.Securités
{

  public static class MathUtil
  {

	// Calculer le Checksum de 'buffer' passé en paramètre
    public static long ComputeChecksum(byte[] buffer)
    {
      return ComputeChecksum(buffer, 0);
    }

	// Calculer le checksum de 'buffer' passé en paramètre à partr de l'index 'décalage'
    public static long ComputeChecksum(byte[] buffer, int décalage)
    {
      long sum = 0;
      for (int i = 0; i < buffer.Length; i++)
      {
        sum += buffer[i] * (i + 1 + décalage);
      }
      return sum;
    }

	// Calculer le checksum d'un fichier
    public static long ComputeChecksum(string nomFichier)
    {

      long sum = 0;
      int bufSize = 4096;

      using (FileStream fs = new FileStream(nomFichier, FileMode.Open, FileAccess.Read))
      using (BinaryReader r = new BinaryReader(fs))
      {
        byte[] readChar = null;
        int décalage = 0;

        do
        {
		 // Lire les caractères
          readChar = r.ReadBytes(bufSize);
          sum += ComputeChecksum(readChar, décalage);
          décalage += readChar.Length;
        } while ((readChar != null) && (readChar.Length > 0));

        r.Close();
      }

      return sum;
    }
  }
}