Base64 Encoder/Decoder in C#

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Introduction

The code implements the encoding and decoding mechanism of Base64, which is widely used in e-Mail encoding and also .NET Viewstate encoding.

Background

It is written based on RFC 1341, using VS.NET 2003.

Notes

I didn't implement filtering and inserting carriage return and newline etc.

Code Listing

Encoder source

using System;

namespace TestBase64
{
  /// <summary>
  /// Summary description for Base64Encoder.
  /// </summary>
  public class Base64Encoder
  {
    byte[] source;
    int length,length2;
    int blockCount;
    int paddingCount;
    public Base64Encoder(byte[] input)
    {
      source=input;
      length=input.Length;
      if((length % 3)==0)
      {
        paddingCount=0;
        blockCount=length/3;
      }
      else
      {
        paddingCount=3-(length % 3);//need to add padding
        blockCount=(length+paddingCount) / 3;
      }
      length2=length+paddingCount;//or blockCount *3
    }

    public char[] GetEncoded()
    {
      byte[] source2;
      source2=new byte[length2];
      //copy data over insert padding
      for (int x=0; x<length2;x++)
      {
        if (x<length)
        {
          source2[x]=source[x];
        }
        else
        {
          source2[x]=0;
        }
      }
      
      byte b1, b2, b3;
      byte temp, temp1, temp2, temp3, temp4;
      byte[] buffer=new byte[blockCount*4];
      char[] result=new char[blockCount*4];
      for (int x=0;x<blockCount;x++)
      {
        b1=source2[x*3];
        b2=source2[x*3+1];
        b3=source2[x*3+2];

        temp1=(byte)((b1 & 252)>>2);//first

        temp=(byte)((b1 & 3)<<4);
        temp2=(byte)((b2 & 240)>>4);
        temp2+=temp; //second

        temp=(byte)((b2 & 15)<<2);
        temp3=(byte)((b3 & 192)>>6);
        temp3+=temp; //third

        temp4=(byte)(b3 & 63); //fourth

        buffer[x*4]=temp1;
        buffer[x*4+1]=temp2;
        buffer[x*4+2]=temp3;
        buffer[x*4+3]=temp4;

      }

      for (int x=0; x<blockCount*4;x++)
      {
        result[x]=sixbit2char(buffer[x]);
      }

      //covert last "A"s to "=", based on paddingCount
      switch (paddingCount)
      {
        case 0:break;
        case 1:result[blockCount*4-1]='=';break;
        case 2:result[blockCount*4-1]='=';
          result[blockCount*4-2]='=';
          break;
        default:break;
      }
      return result;
    }

    private char sixbit2char(byte b)
    {
      char[] lookupTable=new char[64]
          {  'A','B','C','D','E','F','G','H','I','J','K','L','M',
            'N','O','P','Q','R','S','T','U','V','W','X','Y','Z',
            'a','b','c','d','e','f','g','h','i','j','k','l','m',
            'n','o','p','q','r','s','t','u','v','w','x','y','z',
            '0','1','2','3','4','5','6','7','8','9','+','/'};

      if((b>=0) &&(b<=63))
      {
        return lookupTable[(int)b];
      }
      else
      {
        //should not happen;
        return ' ';
      }
    }
  }
}

Decoder source

using System;

namespace TestBase64
{
  /// <summary>
  /// Summary description for Base64Decoder.
  /// </summary>
  public class Base64Decoder
  {
    char[] source;
    int length, length2, length3;
    int blockCount;
    int paddingCount;
    public Base64Decoder(char[] input)
    {
      int temp=0;
      source=input;
      length=input.Length;

      //find how many padding are there
      for (int x=0;x<2;x++)
      {
        if(input[length-x-1]=='=')
          temp++;
      }
      paddingCount=temp;
      //calculate the blockCount;
      //assuming all whitespace and carriage returns/newline were removed.
      blockCount=length/4;
      length2=blockCount*3;
    }

    public byte[] GetDecoded()
    {
      byte[] buffer=new byte[length];//first conversion result
      byte[] buffer2=new byte[length2];//decoded array with padding

      for(int x=0;x<length;x++)
      {
        buffer[x]=char2sixbit(source[x]);
      }

      byte b, b1,b2,b3;
      byte temp1, temp2, temp3, temp4;

      for(int x=0;x<blockCount;x++)
      {
        temp1=buffer[x*4];
        temp2=buffer[x*4+1];
        temp3=buffer[x*4+2];
        temp4=buffer[x*4+3];        

        b=(byte)(temp1<<2);
        b1=(byte)((temp2 & 48)>>4);
        b1+=b;

        b=(byte)((temp2 & 15)<<4);
        b2=(byte)((temp3 & 60)>>2);
        b2+=b;

        b=(byte)((temp3 & 3)<<6);
        b3=temp4;
        b3+=b;

        buffer2[x*3]=b1;
        buffer2[x*3+1]=b2;
        buffer2[x*3+2]=b3;
      }
      //remove paddings
      length3=length2-paddingCount;
      byte[] result=new byte[length3];

      for(int x=0;x<length3;x++)
      {
        result[x]=buffer2[x];
      }

      return result;
    }

    private byte char2sixbit(char c)
    {
      char[] lookupTable=new char[64]
          {  

    'A','B','C','D','E','F','G','H','I','J','K','L','M','N',
    'O','P','Q','R','S','T','U','V','W','X','Y', 'Z',
    'a','b','c','d','e','f','g','h','i','j','k','l','m','n',
    'o','p','q','r','s','t','u','v','w','x','y','z',
    '0','1','2','3','4','5','6','7','8','9','+','/'};
      if(c=='=')
        return 0;
      else
      {
        for (int x=0;x<64;x++)
        {
          if (lookupTable[x]==c)
            return (byte)x;
        }
        //should not reach here
        return 0;
      }

    }

  }
}

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