/src/Utilities/MD5.java

package Utilities;

//package com.twmacinta.util;

import java.io.*;

/**
 * Fast implementation of RSA's MD5 hash generator in Java JDK Beta-2 or higher.
 * <p>
 * Originally written by Santeri Paavolainen, Helsinki Finland 1996.<br>
 * (c) Santeri Paavolainen, Helsinki Finland 1996<br>
 * Many changes Copyright (c) 2002 - 2005 Timothy W Macinta<br>
 * <p>
 * This library is free software; you can redistribute it and/or
 * modify it under the terms of the GNU Library General Public
 * License as published by the Free Software Foundation; either
 * version 2.1 of the License, or (at your option) any later version.
 * <p>
 * This library 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
 * Library General Public License for more details.
 * <p>
 * You should have received a copy of the GNU Library General Public
 * License along with this library; if not, write to the Free
 * Software Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
 * <p>
 * See http://www.twmacinta.com/myjava/fast_md5.php for more information
 * on this file and the related files.
 * <p>
 * This was originally a rather straight re-implementation of the
 * reference implementation given in RFC1321 by RSA.  It passes the MD5
 * test suite as defined in RFC1321.
 * <p>
 * Many optimizations made by Timothy W Macinta.  Reduced time to checksum a
 * test file in Java alone to roughly half the time taken compared with
 * java.security.MessageDigest (within an intepretter).  Also added an
 * optional native method to reduce the time even further.
 * See http://www.twmacinta.com/myjava/fast_md5.php for further information
 * on the time improvements achieved.
 * <p>
 * Some bug fixes also made by Timothy W Macinta.
 * <p>
 * Please note: I (Timothy Macinta) have put this code in the
 * com.twmacinta.util package only because it came without a package.  I
 * was not the the original author of the code, although I did
 * optimize it (substantially) and fix some bugs.
 * <p>
 * This Java class has been derived from the RSA Data Security, Inc. MD5 
 * Message-Digest Algorithm and its reference implementation.
 * <p>
 * This class will attempt to use a native method to quickly compute
 * checksums when the appropriate native library is available.  On Linux,
 * this library should be named "MD5.so" and on Windows it should be
 * named "MD5.dll".  The code will attempt to locate the library in the
 * following locations in the order given:
 *
 * <ol>
 *   <li>The path specified by the system property
 *       "com.twmacinta.util.MD5.NATIVE_LIB_FILE"
 *        (be sure to include "MD5.so" or "MD5.dll"
 *        as appropriate at the end of the path).
 *   <li>A platform specific directory beneath the "lib/arch/" directory.
 *       On Linux for x86, this is "lib/arch/linux_x86/".  On Windows for
 *       x86, this is "lib/arch/win32_x86/".
 *   <li>Within the "lib/" directory.
 *   <li>Within the current directory.
 * </ol>
 *
 * <p>
 * If the library is not found, the code will fall back to the default
 * (slower) Java code.
 * <p>
 * As a side effect of having the code search for the native library,
 * SecurityExceptions might be thrown on JVMs that have a restrictive
 * SecurityManager.  The initialization code attempts to silently discard
 * these exceptions and continue, but many SecurityManagers will
 * attempt to notify the user directly of all SecurityExceptions thrown.
 * Consequently, the code has provisions for skipping the search for
 * the native library.  Any of these provisions may be used to skip the
 * search as long as they are performed <i>before</i> the first
 * instance of a com.twmacinta.util.MD5 object is constructed (note that
 * the convenience stream objects will implicitly create an MD5 object).
 * <p>
 * The first option is to set the system property
 * "com.twmacinta.util.MD5.NO_NATIVE_LIB" to "true" or "1".
 * Unfortunately, SecurityManagers may also choose to disallow system
 * property setting, so this won't be of use in all cases.
 * <p>
 * The second option is to call
 * com.twmacinta.util.MD5.initNativeLibrary(true) before any MD5 objects
 * are constructed.
 *
 * @author	Santeri Paavolainen <sjpaavol@cc.helsinki.fi>
 * @author	Timothy W Macinta (twm@alum.mit.edu) (optimizations and bug fixes)
 */

public class MD5 {
  /**
   * MD5 state
   */
  MD5State	state;
 
  /**
   * If Final() has been called, finals is set to the current finals
   * state. Any Update() causes this to be set to null.
   */
  MD5State 	finals;

  /** 
   * Padding for Final()
   */
  static byte	padding[] = {
    (byte) 0x80, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 
    0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 
    0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0
  };

  private static boolean native_lib_loaded = false;
  private static boolean native_lib_init_pending = false;
  
  /**
   * Initialize MD5 internal state (object can be reused just by
   * calling Init() after every Final()
   */
  public synchronized void Init () {
    state = new MD5State();
    finals = null;
  }

  /**
   * Class constructor
   */
  public MD5 () {
    if (native_lib_init_pending) _initNativeLibrary();
    this.Init();
  }

  /**
   * Initialize class, and update hash with ob.toString()
   *
   * @param	ob	Object, ob.toString() is used to update hash
   *			after initialization
   */
  public MD5 (Object ob) {
    this();
    Update(ob.toString());
  }

  private void Decode (byte buffer[], int shift, int[] out) {
    /*len += shift;
    for (int i = 0; shift < len; i++, shift += 4) {
      out[i] = ((int) (buffer[shift] & 0xff)) |
	(((int) (buffer[shift + 1] & 0xff)) << 8) |
	(((int) (buffer[shift + 2] & 0xff)) << 16) |
	(((int)  buffer[shift + 3]) << 24);
    }*/

    // unrolled loop (original loop shown above)

    out[0] = ((int) (buffer[shift] & 0xff)) |
      (((int) (buffer[shift + 1] & 0xff)) << 8) |
      (((int) (buffer[shift + 2] & 0xff)) << 16) |
      (((int)  buffer[shift + 3]) << 24);
    out[1] = ((int) (buffer[shift + 4] & 0xff)) |
      (((int) (buffer[shift + 5] & 0xff)) << 8) |
      (((int) (buffer[shift + 6] & 0xff)) << 16) |
      (((int)  buffer[shift + 7]) << 24);
    out[2] = ((int) (buffer[shift + 8] & 0xff)) |
      (((int) (buffer[shift + 9] & 0xff)) << 8) |
      (((int) (buffer[shift + 10] & 0xff)) << 16) |
      (((int)  buffer[shift + 11]) << 24);
    out[3] = ((int) (buffer[shift + 12] & 0xff)) |
      (((int) (buffer[shift + 13] & 0xff)) << 8) |
      (((int) (buffer[shift + 14] & 0xff)) << 16) |
      (((int)  buffer[shift + 15]) << 24);
    out[4] = ((int) (buffer[shift + 16] & 0xff)) |
      (((int) (buffer[shift + 17] & 0xff)) << 8) |
      (((int) (buffer[shift + 18] & 0xff)) << 16) |
      (((int)  buffer[shift + 19]) << 24);
    out[5] = ((int) (buffer[shift + 20] & 0xff)) |
      (((int) (buffer[shift + 21] & 0xff)) << 8) |
      (((int) (buffer[shift + 22] & 0xff)) << 16) |
      (((int)  buffer[shift + 23]) << 24);
    out[6] = ((int) (buffer[shift + 24] & 0xff)) |
      (((int) (buffer[shift + 25] & 0xff)) << 8) |
      (((int) (buffer[shift + 26] & 0xff)) << 16) |
      (((int)  buffer[shift + 27]) << 24);
    out[7] = ((int) (buffer[shift + 28] & 0xff)) |
      (((int) (buffer[shift + 29] & 0xff)) << 8) |
      (((int) (buffer[shift + 30] & 0xff)) << 16) |
      (((int)  buffer[shift + 31]) << 24);
    out[8] = ((int) (buffer[shift + 32] & 0xff)) |
      (((int) (buffer[shift + 33] & 0xff)) << 8) |
      (((int) (buffer[shift + 34] & 0xff)) << 16) |
      (((int)  buffer[shift + 35]) << 24);
    out[9] = ((int) (buffer[shift + 36] & 0xff)) |
      (((int) (buffer[shift + 37] & 0xff)) << 8) |
      (((int) (buffer[shift + 38] & 0xff)) << 16) |
      (((int)  buffer[shift + 39]) << 24);
    out[10] = ((int) (buffer[shift + 40] & 0xff)) |
      (((int) (buffer[shift + 41] & 0xff)) << 8) |
      (((int) (buffer[shift + 42] & 0xff)) << 16) |
      (((int)  buffer[shift + 43]) << 24);
    out[11] = ((int) (buffer[shift + 44] & 0xff)) |
      (((int) (buffer[shift + 45] & 0xff)) << 8) |
      (((int) (buffer[shift + 46] & 0xff)) << 16) |
      (((int)  buffer[shift + 47]) << 24);
    out[12] = ((int) (buffer[shift + 48] & 0xff)) |
      (((int) (buffer[shift + 49] & 0xff)) << 8) |
      (((int) (buffer[shift + 50] & 0xff)) << 16) |
      (((int)  buffer[shift + 51]) << 24);
    out[13] = ((int) (buffer[shift + 52] & 0xff)) |
      (((int) (buffer[shift + 53] & 0xff)) << 8) |
      (((int) (buffer[shift + 54] & 0xff)) << 16) |
      (((int)  buffer[shift + 55]) << 24);
    out[14] = ((int) (buffer[shift + 56] & 0xff)) |
      (((int) (buffer[shift + 57] & 0xff)) << 8) |
      (((int) (buffer[shift + 58] & 0xff)) << 16) |
      (((int)  buffer[shift + 59]) << 24);
    out[15] = ((int) (buffer[shift + 60] & 0xff)) |
      (((int) (buffer[shift + 61] & 0xff)) << 8) |
      (((int) (buffer[shift + 62] & 0xff)) << 16) |
      (((int)  buffer[shift + 63]) << 24);
  }

  private native void Transform_native (int[] state, byte buffer[], int shift, int length);

  private void Transform (MD5State state, byte buffer[], int shift, int[] decode_buf) {
    int	
      a = state.state[0],
      b = state.state[1],
      c = state.state[2],
      d = state.state[3],
      x[] = decode_buf;

    Decode(buffer, shift, decode_buf);
    
    /* Round 1 */
    a += ((b & c) | (~b & d)) + x[ 0] + 0xd76aa478; /* 1 */
    a = ((a << 7) | (a >>> 25)) + b;
    d += ((a & b) | (~a & c)) + x[ 1] + 0xe8c7b756; /* 2 */
    d = ((d << 12) | (d >>> 20)) + a;
    c += ((d & a) | (~d & b)) + x[ 2] + 0x242070db; /* 3 */
    c = ((c << 17) | (c >>> 15)) + d;
    b += ((c & d) | (~c & a)) + x[ 3] + 0xc1bdceee; /* 4 */
    b = ((b << 22) | (b >>> 10)) + c;

    a += ((b & c) | (~b & d)) + x[ 4] + 0xf57c0faf; /* 5 */
    a = ((a << 7) | (a >>> 25)) + b;
    d += ((a & b) | (~a & c)) + x[ 5] + 0x4787c62a; /* 6 */
    d = ((d << 12) | (d >>> 20)) + a;
    c += ((d & a) | (~d & b)) + x[ 6] + 0xa8304613; /* 7 */
    c = ((c << 17) | (c >>> 15)) + d;
    b += ((c & d) | (~c & a)) + x[ 7] + 0xfd469501; /* 8 */
    b = ((b << 22) | (b >>> 10)) + c;

    a += ((b & c) | (~b & d)) + x[ 8] + 0x698098d8; /* 9 */
    a = ((a << 7) | (a >>> 25)) + b;
    d += ((a & b) | (~a & c)) + x[ 9] + 0x8b44f7af; /* 10 */
    d = ((d << 12) | (d >>> 20)) + a;
    c += ((d & a) | (~d & b)) + x[10] + 0xffff5bb1; /* 11 */
    c = ((c << 17) | (c >>> 15)) + d;
    b += ((c & d) | (~c & a)) + x[11] + 0x895cd7be; /* 12 */
    b = ((b << 22) | (b >>> 10)) + c;

    a += ((b & c) | (~b & d)) + x[12] + 0x6b901122; /* 13 */
    a = ((a << 7) | (a >>> 25)) + b;
    d += ((a & b) | (~a & c)) + x[13] + 0xfd987193; /* 14 */
    d = ((d << 12) | (d >>> 20)) + a;
    c += ((d & a) | (~d & b)) + x[14] + 0xa679438e; /* 15 */
    c = ((c << 17) | (c >>> 15)) + d;
    b += ((c & d) | (~c & a)) + x[15] + 0x49b40821; /* 16 */
    b = ((b << 22) | (b >>> 10)) + c;
    
    
    /* Round 2 */
    a += ((b & d) | (c & ~d)) + x[ 1] + 0xf61e2562; /* 17 */
    a = ((a << 5) | (a >>> 27)) + b;
    d += ((a & c) | (b & ~c)) + x[ 6] + 0xc040b340; /* 18 */
    d = ((d << 9) | (d >>> 23)) + a;
    c += ((d & b) | (a & ~b)) + x[11] + 0x265e5a51; /* 19 */
    c = ((c << 14) | (c >>> 18)) + d;
    b += ((c & a) | (d & ~a)) + x[ 0] + 0xe9b6c7aa; /* 20 */
    b = ((b << 20) | (b >>> 12)) + c;

    a += ((b & d) | (c & ~d)) + x[ 5] + 0xd62f105d; /* 21 */
    a = ((a << 5) | (a >>> 27)) + b;
    d += ((a & c) | (b & ~c)) + x[10] + 0x02441453; /* 22 */
    d = ((d << 9) | (d >>> 23)) + a;
    c += ((d & b) | (a & ~b)) + x[15] + 0xd8a1e681; /* 23 */
    c = ((c << 14) | (c >>> 18)) + d;
    b += ((c & a) | (d & ~a)) + x[ 4] + 0xe7d3fbc8; /* 24 */
    b = ((b << 20) | (b >>> 12)) + c;

    a += ((b & d) | (c & ~d)) + x[ 9] + 0x21e1cde6; /* 25 */
    a = ((a << 5) | (a >>> 27)) + b;
    d += ((a & c) | (b & ~c)) + x[14] + 0xc33707d6; /* 26 */
    d = ((d << 9) | (d >>> 23)) + a;
    c += ((d & b) | (a & ~b)) + x[ 3] + 0xf4d50d87; /* 27 */
    c = ((c << 14) | (c >>> 18)) + d;
    b += ((c & a) | (d & ~a)) + x[ 8] + 0x455a14ed; /* 28 */
    b = ((b << 20) | (b >>> 12)) + c;

    a += ((b & d) | (c & ~d)) + x[13] + 0xa9e3e905; /* 29 */
    a = ((a << 5) | (a >>> 27)) + b;
    d += ((a & c) | (b & ~c)) + x[ 2] + 0xfcefa3f8; /* 30 */
    d = ((d << 9) | (d >>> 23)) + a;
    c += ((d & b) | (a & ~b)) + x[ 7] + 0x676f02d9; /* 31 */
    c = ((c << 14) | (c >>> 18)) + d;
    b += ((c & a) | (d & ~a)) + x[12] + 0x8d2a4c8a; /* 32 */
    b = ((b << 20) | (b >>> 12)) + c;
    
    
    /* Round 3 */
    a += (b ^ c ^ d) + x[ 5] + 0xfffa3942;      /* 33 */
    a = ((a << 4) | (a >>> 28)) + b;
    d += (a ^ b ^ c) + x[ 8] + 0x8771f681;      /* 34 */
    d = ((d << 11) | (d >>> 21)) + a;
    c += (d ^ a ^ b) + x[11] + 0x6d9d6122;      /* 35 */
    c = ((c << 16) | (c >>> 16)) + d;
    b += (c ^ d ^ a) + x[14] + 0xfde5380c;      /* 36 */
    b = ((b << 23) | (b >>> 9)) + c;
    
    a += (b ^ c ^ d) + x[ 1] + 0xa4beea44;      /* 37 */
    a = ((a << 4) | (a >>> 28)) + b;
    d += (a ^ b ^ c) + x[ 4] + 0x4bdecfa9;      /* 38 */
    d = ((d << 11) | (d >>> 21)) + a;
    c += (d ^ a ^ b) + x[ 7] + 0xf6bb4b60;      /* 39 */
    c = ((c << 16) | (c >>> 16)) + d;
    b += (c ^ d ^ a) + x[10] + 0xbebfbc70;      /* 40 */
    b = ((b << 23) | (b >>> 9)) + c;
    
    a += (b ^ c ^ d) + x[13] + 0x289b7ec6;      /* 41 */
    a = ((a << 4) | (a >>> 28)) + b;
    d += (a ^ b ^ c) + x[ 0] + 0xeaa127fa;      /* 42 */
    d = ((d << 11) | (d >>> 21)) + a;
    c += (d ^ a ^ b) + x[ 3] + 0xd4ef3085;      /* 43 */
    c = ((c << 16) | (c >>> 16)) + d;
    b += (c ^ d ^ a) + x[ 6] + 0x04881d05;      /* 44 */
    b = ((b << 23) | (b >>> 9)) + c;
    
    a += (b ^ c ^ d) + x[ 9] + 0xd9d4d039;      /* 33 */
    a = ((a << 4) | (a >>> 28)) + b;
    d += (a ^ b ^ c) + x[12] + 0xe6db99e5;      /* 34 */
    d = ((d << 11) | (d >>> 21)) + a;
    c += (d ^ a ^ b) + x[15] + 0x1fa27cf8;      /* 35 */
    c = ((c << 16) | (c >>> 16)) + d;
    b += (c ^ d ^ a) + x[ 2] + 0xc4ac5665;      /* 36 */
    b = ((b << 23) | (b >>> 9)) + c;
    

    /* Round 4 */
    a += (c ^ (b | ~d)) + x[ 0] + 0xf4292244; /* 49 */
    a = ((a << 6) | (a >>> 26)) + b;
    d += (b ^ (a | ~c)) + x[ 7] + 0x432aff97; /* 50 */
    d = ((d << 10) | (d >>> 22)) + a;
    c += (a ^ (d | ~b)) + x[14] + 0xab9423a7; /* 51 */
    c = ((c << 15) | (c >>> 17)) + d;
    b += (d ^ (c | ~a)) + x[ 5] + 0xfc93a039; /* 52 */
    b = ((b << 21) | (b >>> 11)) + c;

    a += (c ^ (b | ~d)) + x[12] + 0x655b59c3; /* 53 */
    a = ((a << 6) | (a >>> 26)) + b;
    d += (b ^ (a | ~c)) + x[ 3] + 0x8f0ccc92; /* 54 */
    d = ((d << 10) | (d >>> 22)) + a;
    c += (a ^ (d | ~b)) + x[10] + 0xffeff47d; /* 55 */
    c = ((c << 15) | (c >>> 17)) + d;
    b += (d ^ (c | ~a)) + x[ 1] + 0x85845dd1; /* 56 */
    b = ((b << 21) | (b >>> 11)) + c;

    a += (c ^ (b | ~d)) + x[ 8] + 0x6fa87e4f; /* 57 */
    a = ((a << 6) | (a >>> 26)) + b;
    d += (b ^ (a | ~c)) + x[15] + 0xfe2ce6e0; /* 58 */
    d = ((d << 10) | (d >>> 22)) + a;
    c += (a ^ (d | ~b)) + x[ 6] + 0xa3014314; /* 59 */
    c = ((c << 15) | (c >>> 17)) + d;
    b += (d ^ (c | ~a)) + x[13] + 0x4e0811a1; /* 60 */
    b = ((b << 21) | (b >>> 11)) + c;

    a += (c ^ (b | ~d)) + x[ 4] + 0xf7537e82; /* 61 */
    a = ((a << 6) | (a >>> 26)) + b;
    d += (b ^ (a | ~c)) + x[11] + 0xbd3af235; /* 62 */
    d = ((d << 10) | (d >>> 22)) + a;
    c += (a ^ (d | ~b)) + x[ 2] + 0x2ad7d2bb; /* 63 */
    c = ((c << 15) | (c >>> 17)) + d;
    b += (d ^ (c | ~a)) + x[ 9] + 0xeb86d391; /* 64 */
    b = ((b << 21) | (b >>> 11)) + c;

    state.state[0] += a;
    state.state[1] += b;
    state.state[2] += c;
    state.state[3] += d;
  }

  /**	
   * Updates hash with the bytebuffer given (using at maximum length bytes from
   * that buffer)
   *
   * @param stat	Which state is updated
   * @param buffer	Array of bytes to be hashed
   * @param offset	Offset to buffer array
   * @param length	Use at maximum `length' bytes (absolute
   *			maximum is buffer.length)
   */
  public void Update (MD5State stat, byte buffer[], int offset, int length) {
    int	index, partlen, i, start;
    finals = null;

    /* Length can be told to be shorter, but not inter */
    if ((length - offset)> buffer.length)
      length = buffer.length - offset;

    /* compute number of bytes mod 64 */

    index = (int) (stat.count & 0x3f);
    stat.count += length;
    
    partlen = 64 - index;

    if (length >= partlen) {
      if (native_lib_loaded) {
	
	// update state (using native method) to reflect input

	if (partlen == 64) {
	  partlen = 0;
	} else {
	  for (i = 0; i < partlen; i++)
	    stat.buffer[i + index] = buffer[i + offset];
	  Transform_native(stat.state, stat.buffer, 0, 64);
	}
	Transform_native(stat.state, buffer, partlen + offset, length - partlen);
	i = partlen + ((length - partlen) / 64) * 64;
      } else {
	
	// update state (using only Java) to reflect input

	int[] decode_buf = new int[16];
	if (partlen == 64) {
	  partlen = 0;
	} else {
	  for (i = 0; i < partlen; i++)
	    stat.buffer[i + index] = buffer[i + offset];
	  Transform(stat, stat.buffer, 0, decode_buf);
	}
	for (i = partlen; (i + 63) < length; i+= 64) {
	  Transform(stat, buffer, i + offset, decode_buf);
	}
      }
      index = 0;
    } else 
      i = 0;

    /* buffer remaining input */
    if (i < length) {
      start = i;
      for (; i < length; i++) {
	stat.buffer[index + i - start] = buffer[i + offset];
      }
    }
  }

  /* 
   * Update()s for other datatypes than byte[] also. Update(byte[], int)
   * is only the main driver.
   */

  /**
   * Plain update, updates this object
   */

  public void Update (byte buffer[], int offset, int length) {
      Update(this.state, buffer, offset, length);
  }

  public void Update (byte buffer[], int length) {
      Update(this.state, buffer, 0, length);
  }

  /**
   * Updates hash with given array of bytes
   *
   * @param buffer	Array of bytes to use for updating the hash
   */
  public void Update (byte buffer[]) {
      Update(buffer, 0, buffer.length);
  }

  /**
   * Updates hash with a single byte
   *
   * @param b		Single byte to update the hash
   */
  public void Update (byte b) {
    byte buffer[] = new byte[1];
    buffer[0] = b;

    Update(buffer, 1);
  }
  
  /**
   * Update buffer with given string.  Note that because the version of
   * the s.getBytes() method without parameters is used to convert the
   * string to a byte array, the results of this method may be different
   * on different platforms.  The s.getBytes() method converts the string
   * into a byte array using the current platform's default character set
   * and may therefore have different results on platforms with different
   * default character sets.  If a version that works consistently
   * across platforms with different default character sets is desired,
   * use the overloaded version of the Update() method which takes a
   * string and a character encoding.
   *
   * @param s		String to be update to hash (is used as
   *		       	s.getBytes())
   */
  public void Update (String s) {
    byte chars[] = s.getBytes();
    Update(chars, chars.length);
  }

  /**
   * Update buffer with given string using the given encoding.  If the
   * given encoding is null, the encoding "ISO8859_1" is used.
   *
   * @param s		String to be update to hash (is used as
   *		       	s.getBytes(charset_name))
   * @param charset_name The character set to use to convert s to a
   *                    byte array, or null if the "ISO8859_1"
   *                    character set is desired.
   * @exception         java.io.UnsupportedEncodingException If the named
   *                    charset is not supported.
   */
  public void Update (String s, String charset_name) throws java.io.UnsupportedEncodingException {
    if (charset_name == null) charset_name = "ISO8859_1";
    byte chars[] = s.getBytes(charset_name);
    Update(chars, chars.length);
  }

  /**
   * Update buffer with a single integer (only & 0xff part is used,
   * as a byte)
   *
   * @param i		Integer value, which is then converted to 
   *			byte as i & 0xff
   */

  public void Update (int i) {
      Update((byte) (i & 0xff));
  }

  private byte[] Encode (int input[], int len) {
    int		i, j;
    byte	out[];

    out = new byte[len];

    for (i = j = 0; j  < len; i++, j += 4) {
      out[j] = (byte) (input[i] & 0xff);
      out[j + 1] = (byte) ((input[i] >>> 8) & 0xff);
      out[j + 2] = (byte) ((input[i] >>> 16) & 0xff);
      out[j + 3] = (byte) ((input[i] >>> 24) & 0xff);
    }

    return out;
  }

  /**
   * Returns array of bytes (16 bytes) representing hash as of the
   * current state of this object. Note: getting a hash does not
   * invalidate the hash object, it only creates a copy of the real
   * state which is finalized. 
   *
   * @return	Array of 16 bytes, the hash of all updated bytes
   */
  public synchronized byte[] Final () {
    byte	bits[];
    int		index, padlen;
    MD5State	fin;

    if (finals == null) {
      fin = new MD5State(state);

      int[] count_ints = {(int) (fin.count << 3), (int) (fin.count >> 29)};
      bits = Encode(count_ints, 8);
    
      index = (int) (fin.count & 0x3f);
      padlen = (index < 56) ? (56 - index) : (120 - index);

      Update(fin, padding, 0, padlen);
      Update(fin, bits, 0, 8);	

      /* Update() sets finals to null */
      finals = fin;
    } 

    return Encode(finals.state, 16);
  }    

  private static final char[] HEX_CHARS = {'0', '1', '2', '3',
					   '4', '5', '6', '7',
					   '8', '9', 'a', 'b',
					   'c', 'd', 'e', 'f',};

  /**
   * Turns array of bytes into string representing each byte as
   * unsigned hex number.
   * 
   * @param hash	Array of bytes to convert to hex-string
   * @return	Generated hex string
   */
  public static String asHex (byte hash[]) {
    char buf[] = new char[hash.length * 2];
    for (int i = 0, x = 0; i < hash.length; i++) {
      buf[x++] = HEX_CHARS[(hash[i] >>> 4) & 0xf];
      buf[x++] = HEX_CHARS[hash[i] & 0xf];
    }
    return new String(buf);
  }

  /**
   * Returns 32-character hex representation of this objects hash
   *
   * @return String of this object's hash
   */
  public String asHex () {
    return asHex(this.Final());
  }

  public static synchronized final void initNativeLibrary(boolean disallow_lib_loading) {
    if (disallow_lib_loading) {
      native_lib_init_pending = false;
    } else {
      _initNativeLibrary();
    }
  }

  private static synchronized final void  _initNativeLibrary() {
    if (!native_lib_init_pending) return;
    native_lib_loaded = _loadNativeLibrary();
    native_lib_init_pending = false;
  }

  private static synchronized final boolean _loadNativeLibrary() {
    try {

      // don't try to load if the right property is set

      String prop = System.getProperty("com.twmacinta.util.MD5.NO_NATIVE_LIB");
      if (prop != null) {
	prop = prop.trim();
	if (prop.equalsIgnoreCase("true") || prop.equals("1")) return false;
      }

      // the library to load can be specified as a property

      File f;
      prop = System.getProperty("com.twmacinta.util.MD5.NATIVE_LIB_FILE");
      if (prop != null) {
	f = new File(prop);
	if (f.canRead()) {
	  System.load(f.getAbsolutePath());
	  return true;
	}
      }

      // determine the operating system and architecture

      String os_name = System.getProperty("os.name");
      String os_arch = System.getProperty("os.arch");
      if (os_name == null || os_arch == null) return false;
      os_name = os_name.toLowerCase();
      os_arch = os_arch.toLowerCase();

      // define settings which are OS arch architecture independent

      File arch_lib_path = null;
      String arch_libfile_suffix = null;

    //   fill in settings for Linux on x86

      if (os_name.equals("linux") &&
	  (os_arch.equals("x86") ||
	   os_arch.equals("i386") ||
	   os_arch.equals("i486") ||
	   os_arch.equals("i586") ||
	   os_arch.equals("i686"))) {
	arch_lib_path = new File(new File(new File("lib"), "arch"), "linux_x86");
	arch_libfile_suffix = ".so"; 

	// fill in settings for Windows on x86

      } else if (os_name.startsWith("windows ") &&
		 (os_arch.equals("x86") ||
		  os_arch.equals("i386") ||
		  os_arch.equals("i486") ||
		  os_arch.equals("i586") ||
		  os_arch.equals("i686"))) {
	arch_lib_path = new File(new File(new File("lib"), "arch"), "win32_x86");
	arch_libfile_suffix = ".dll"; 

	// fill in settings Mac OS X on PPC

      } else if (os_name.startsWith("mac os x") &&
		 (os_arch.equals("ppc"))) {
	arch_lib_path = new File(new File(new File("lib"), "arch"), "darwin_ppc");
	arch_libfile_suffix = ".jnilib";

	// default to .so files with no architecture specific subdirectory
      
      } else {
	arch_libfile_suffix = ".so"; 
      }

      // build the required filename

      String fname = "MD5" + arch_libfile_suffix;

      // try the architecture specific directory

      if (arch_lib_path != null) {
	f = new File(arch_lib_path, fname);
	if (f.canRead()) {
	  System.load(f.getAbsolutePath());
	  return true;
	}
      }

      // try the "lib" subdirectory

      f = new File(new File("lib"), fname);
      if (f.canRead()) {
	System.load(f.getAbsolutePath());
	return true;
      }

      // try the working directory

      f = new File(fname);
      if (f.canRead()) {
	System.load(f.getAbsolutePath());
	return true;
      }
      
      // discard SecurityExceptions

    } catch (SecurityException e) {}

    // unable to load

    return false;
  }

  /**
   * Calculates and returns the hash of the contents of the given file.
   **/
  public static byte[] getHash(File f) throws IOException {
    if (!f.exists()) throw new FileNotFoundException(f.toString());
    InputStream close_me = null;
    try {
      long buf_size = f.length();
      if (buf_size < 512) buf_size = 512;
      if (buf_size > 65536) buf_size = 65536;
      byte[] buf = new byte[(int) buf_size];
      MD5InputStream in = new MD5InputStream(new FileInputStream(f));
      close_me = in;
      while (in.read(buf) != -1);
      in.close();
      return in.hash();
    } catch (IOException e) {
      if (close_me != null) try { close_me.close(); } catch (Exception e2) {}
      throw e;
    }
  }

  /**
   * @return true iff the first 16 bytes of both hash1 and hash2 are
   *         equal;  both hash1 and hash2 are null; or either hash
   *         array is less than 16 bytes in length and their lengths and
   *         all of their bytes are equal.
   **/
  public static boolean hashesEqual(byte[] hash1, byte[] hash2) {
    if (hash1 == null) return hash2 == null;
    if (hash2 == null) return false;
    int targ = 16;
    if (hash1.length < 16) {
      if (hash2.length != hash1.length) return false;
      targ = hash1.length;
    } else if (hash2.length < 16) {
      return false;
    }
    for (int i = 0; i < targ; i++) {
      if (hash1[i] != hash2[i]) return false;
    }
    return true;
  }

}