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There is a newer version: 0.0.20
/*
 * This file is part of the SCUBA smart card framework.
 *
 * This library is free software; you can redistribute it and/or
 * modify it under the terms of the GNU Lesser General Public
 * License as published by the Free Software Foundation; either
 * version 2.1 of the License, or (at your option) any later version.
 *
 * 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
 * Lesser General Public License for more details.
 *
 * You should have received a copy of the GNU Lesser General Public
 * License along with this library; if not, write to the Free Software
 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
 *
 * Copyright (C) 2009 - 2015 The SCUBA team.
 *
 * $Id: TLVUtil.java 246 2015-04-09 08:13:52Z martijno $
 */

package net.sf.scuba.tlv;

import java.io.ByteArrayOutputStream;

/* FIXME: make class package visible only. */

public class TLVUtil implements ASN1Constants {
	
	/** Hide from public interface. */
	private TLVUtil() {
	}
	
	public static boolean isPrimitive(int tag) {
		int i = 3;
		for (; i >= 0; i--) {
			int mask = (0xFF << (8 * i));
			if ((tag & mask) != 0x00) { break; }
		}
		int msByte = (((tag & (0xFF << (8 * i))) >> (8 * i)) & 0xFF);
		boolean result = ((msByte & 0x20) == 0x00);
		return result;
	}

	public static int getTagLength(int tag) {
		return getTagAsBytes(tag).length;
	}

	public static int getLengthLength(int length) {
		return getLengthAsBytes(length).length;
	}

	/**
	 * The tag bytes of this object.
	 * 
	 * @param tag the tag
	 * 
	 * @return the tag bytes of this object.
	 */
	public static byte[] getTagAsBytes(int tag) {
		ByteArrayOutputStream out = new ByteArrayOutputStream();
		int byteCount = (int)(Math.log(tag) / Math.log(256)) + 1;
		for (int i = 0; i < byteCount; i++) {
			int pos = 8 * (byteCount - i - 1);
			out.write((tag & (0xFF << pos)) >> pos);
		}
		byte[] tagBytes = out.toByteArray();
		switch (getTagClass(tag)) {
		case APPLICATION_CLASS:
			tagBytes[0] |= 0x40;
			break;
		case CONTEXT_SPECIFIC_CLASS:
			tagBytes[0] |= 0x80;
			break;
		case PRIVATE_CLASS:
			tagBytes[0] |= 0xC0;
			break;
		}
		if (!isPrimitive(tag)) {
			tagBytes[0] |= 0x20;
		}
		return tagBytes;
	}

	/**
	 * The length bytes of this object.
	 *
	 * @param length the length
	 *
	 * @return length of encoded value as bytes
	 */
	public static byte[] getLengthAsBytes(int length) {
		ByteArrayOutputStream out = new ByteArrayOutputStream();
		if (length < 0x80) {
			/* short form */
			out.write(length);
		} else {
			int byteCount = log(length, 256);
			out.write(0x80 | byteCount);
			for (int i = 0; i < byteCount; i++) {
				int pos = 8 * (byteCount - i - 1);
				out.write((length & (0xFF << pos)) >> pos);
			}
		}
		return out.toByteArray();
	}

	static int getTagClass(int tag) {
		int i = 3;
		for (; i >= 0; i--) {
			int mask = (0xFF << (8 * i));
			if ((tag & mask) != 0x00) { break; }
		}
		int msByte = (((tag & (0xFF << (8 * i))) >> (8 * i)) & 0xFF);
		switch (msByte & 0xC0) {
		case 0x00: return UNIVERSAL_CLASS;
		case 0x40: return APPLICATION_CLASS;
		case 0x80: return CONTEXT_SPECIFIC_CLASS;
		case 0xC0:
		default: return PRIVATE_CLASS;
		}
	}

	private static int log(int n, int base) {
		int result = 0;
		while (n > 0) {
			n = n / base;
			result ++;
		}
		return result;
	}
}