content: package local.org.bouncycastle.util.encoders;
  
  import java.io.IOException;
  import java.io.OutputStream;
  
  public class HexEncoder
      implements Encoder
  {
      protected final byte[] encodingTable =
          {
              (byte)'0', (byte)'1', (byte)'2', (byte)'3', (byte)'4', (byte)'5', (byte)'6', (byte)'7',
              (byte)'8', (byte)'9', (byte)'a', (byte)'b', (byte)'c', (byte)'d', (byte)'e', (byte)'f'
          };
      
      /*
       * set up the decoding table.
       */
      protected final byte[] decodingTable = new byte[128];
  
      protected void initialiseDecodingTable()
      {
          for (int i = 0; i < decodingTable.length; i++)
          {
              decodingTable[i] = (byte)0xff;
          }
  
          for (int i = 0; i < encodingTable.length; i++)
          {
              decodingTable[encodingTable[i]] = (byte)i;
          }
          
          decodingTable['A'] = decodingTable['a'];
          decodingTable['B'] = decodingTable['b'];
          decodingTable['C'] = decodingTable['c'];
          decodingTable['D'] = decodingTable['d'];
          decodingTable['E'] = decodingTable['e'];
          decodingTable['F'] = decodingTable['f'];
      }
      
      public HexEncoder()
      {
          initialiseDecodingTable();
      }
      
      /**
       * encode the input data producing a Hex output stream.
       *
       * @return the number of bytes produced.
       */
      public int encode(
          byte[]                data,
          int                    off,
          int                    length,
          OutputStream    out) 
          throws IOException
      {        
          for (int i = off; i < (off + length); i++)
          {
              int    v = data[i] & 0xff;
  
              out.write(encodingTable[(v >>> 4)]);
              out.write(encodingTable[v & 0xf]);
          }
  
          return length * 2;
      }
  
      private static boolean ignore(
          char    c)
      {
          return c == '\n' || c =='\r' || c == '\t' || c == ' ';
      }
  
      /**
       * decode the Hex encoded byte data writing it to the given output stream,
       * whitespace characters will be ignored.
       *
       * @return the number of bytes produced.
       */
      public int decode(
          byte[]          data,
          int             off,
          int             length,
          OutputStream    out)
          throws IOException
      {
          byte    b1, b2;
          int     outLen = 0;
          
          int     end = off + length;
          
          while (end > off)
          {
              if (!ignore((char)data[end - 1]))
              {
                  break;
              }
              
              end--;
          }
          
          int i = off;
          while (i < end)
          {
              while (i < end && ignore((char)data[i]))
              {
                  i++;
              }
              
              b1 = decodingTable[data[i++]];
              
              while (i < end && ignore((char)data[i]))
              {
                  i++;
              }
              
              b2 = decodingTable[data[i++]];
  
              if ((b1 | b2) < 0)
              {
                  throw new IOException("invalid characters encountered in Hex data");
              }
  
              out.write((b1 << 4) | b2);
              
              outLen++;
          }
  
          return outLen;
      }
      
      /**
       * decode the Hex encoded String data writing it to the given output stream,
       * whitespace characters will be ignored.
       *
       * @return the number of bytes produced.
       */
      public int decode(
          String          data,
          OutputStream    out)
          throws IOException
      {
          byte    b1, b2;
          int     length = 0;
          
          int     end = data.length();
          
          while (end > 0)
          {
              if (!ignore(data.charAt(end - 1)))
              {
                  break;
              }
              
              end--;
          }
          
          int i = 0;
          while (i < end)
          {
              while (i < end && ignore(data.charAt(i)))
              {
                  i++;
              }
              
              b1 = decodingTable[data.charAt(i++)];
              
              while (i < end && ignore(data.charAt(i)))
              {
                  i++;
              }
              
              b2 = decodingTable[data.charAt(i++)];
  
              if ((b1 | b2) < 0)
              {
                  throw new IOException("invalid characters encountered in Hex string");
              }
  
              out.write((b1 << 4) | b2);
              
              length++;
          }
  
          return length;
      }
  }
  