multiprecision.java

面向应用的智能安全代理平台和工具包是一个综合网络应用的安全共性需求而设计和实现的一个通用性的网络信息安全应用支撑平台

package au.net.aba.pgp;

/*
 * $Id: Multiprecision.java,v 1.2 1998/10/19 06:32:40 leachbj Exp $
 * $Author: leachbj $
 *
 * Copyright (C) 1996-1998 Australian Business Access Pty Ltd.
 * All rights reserved.
 * 
 * Use, modification, copying and distribution of this software is subject the
 * terms and conditions of the ABA Public Licence. See the file
 * "PUBLIC_LICENCE" for additional information.
 *
 * If you have not received a copy of the Public Licence, you must destroy all
 * copies of this file immediately. 
 *
 * $Source: /aba/CVSROOT/jdk1.1/src/au.net.aba/pgp/Multiprecision.java,v $
 * $Revision: 1.2 $
 * $Date: 1998/10/19 06:32:40 $
 * $State: Exp $
 */

import java.io.*;

import java.math.*;

/**
 * A simple multiprecision integer class that manipulates large integers
 * in a form compatible with the PGP representation.
 */
class Multiprecision
{
	public final static String ident = "$Id: Multiprecision.java,v 1.2 1998/10/19 06:32:40 leachbj Exp $";

	public int bits;		// bits of precision (exact)
	public byte[] octet;		// bytes of value (octet[0] == LSB)


	//
	// Construct from an input stream.
	//
	public Multiprecision (InputStream input)
		throws IOException
	{
		// read number of bits
		DataInputStream data = new DataInputStream (input);
		bits = data.readUnsignedShort ();

		// non zero length?
		if (bits > 0){
			// read bytes of value
			int length = (bits >> 3)
				+ ((bits & 0x07) == 0 ? 0 : 1);
			octet = new byte[length];
			data.readFully (octet);
		}
	}
	/**
	 * convert this to a BigInteger
	 */
	public BigInteger toBigInteger()
	{
						// we assume always non-zero
		return new BigInteger(1, octet);
	}
	//
	// Convert to a string.
	//
	public String toString ()
	{
		String s = "";
		for (int i = 0; i < octet.length; i++){
			if ((octet[i] & 0xff) < 16){
				s += "0";
			}
			s += Integer.toString (octet[i] & 0xff,16);
		}

		return (s);
	}
}