content: package local.org.bouncycastle.crypto.digests;
  
  import local.org.bouncycastle.crypto.ExtendedDigest;
  import local.org.bouncycastle.util.Memoable;
  
  /**
   * base implementation of MD4 family style digest as outlined in
   * "Handbook of Applied Cryptography", pages 344 - 347.
   */
  public abstract class GeneralDigest
      implements ExtendedDigest, Memoable
  {
      private static final int BYTE_LENGTH = 64;
      private byte[]  xBuf;
      private int     xBufOff;
  
      private long    byteCount;
  
      /**
       * Standard constructor
       */
      protected GeneralDigest()
      {
          xBuf = new byte[4];
          xBufOff = 0;
      }
  
      /**
       * Copy constructor.  We are using copy constructors in place
       * of the Object.clone() interface as this interface is not
       * supported by J2ME.
       */
      protected GeneralDigest(GeneralDigest t)
      {
          xBuf = new byte[t.xBuf.length];
  
          copyIn(t);
      }
  
      protected void copyIn(GeneralDigest t)
      {
          System.arraycopy(t.xBuf, 0, xBuf, 0, t.xBuf.length);
  
          xBufOff = t.xBufOff;
          byteCount = t.byteCount;
      }
  
      public void update(
          byte in)
      {
          xBuf[xBufOff++] = in;
  
          if (xBufOff == xBuf.length)
          {
              processWord(xBuf, 0);
              xBufOff = 0;
          }
  
          byteCount++;
      }
  
      public void update(
          byte[]  in,
          int     inOff,
          int     len)
      {
          //
          // fill the current word
          //
          while ((xBufOff != 0) && (len > 0))
          {
              update(in[inOff]);
  
              inOff++;
              len--;
          }
  
          //
          // process whole words.
          //
          while (len > xBuf.length)
          {
              processWord(in, inOff);
  
              inOff += xBuf.length;
              len -= xBuf.length;
              byteCount += xBuf.length;
          }
  
          //
          // load in the remainder.
          //
          while (len > 0)
          {
              update(in[inOff]);
  
              inOff++;
              len--;
          }
      }
  
      public void finish()
      {
          long    bitLength = (byteCount << 3);
  
          //
          // add the pad bytes.
          //
          update((byte)128);
  
          while (xBufOff != 0)
          {
              update((byte)0);
          }
  
          processLength(bitLength);
  
          processBlock();
      }
  
      public void reset()
      {
          byteCount = 0;
  
          xBufOff = 0;
          for (int i = 0; i < xBuf.length; i++)
          {
              xBuf[i] = 0;
          }
      }
  
      public int getByteLength()
      {
          return BYTE_LENGTH;
      }
      
      protected abstract void processWord(byte[] in, int inOff);
  
      protected abstract void processLength(long bitLength);
  
      protected abstract void processBlock();
  }
  