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jBasics is a collection of useful utility classes for Java. This includes helper for XML, mathematic functions, restful web services helper, pattern oriented programming interfaces and more. Currently Java7 and up is supported. Version 1.0 will required at leaset Java8.

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/*
 * Copyright (c) 2009-2015
 * 	IT-Consulting Stephan Schloepke (http://www.schloepke.de/)
 * 	klemm software consulting Mirko Klemm (http://www.klemm-scs.com/)
 *
 * Permission is hereby granted, free of charge, to any person obtaining a copy
 * of this software and associated documentation files (the "Software"), to deal
 * in the Software without restriction, including without limitation the rights
 * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
 * copies of the Software, and to permit persons to whom the Software is
 * furnished to do so, subject to the following conditions:
 *
 * The above copyright notice and this permission notice shall be included in
 * all copies or substantial portions of the Software.
 *
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
 * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
 * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
 * THE SOFTWARE.
 */
package org.jbasics.math.obsolete;

import org.jbasics.arrays.ArrayConstants;

/**
 * Helper class to deal with Sign/Magnitude arrays. That is an array representing a big integer number in form of
 * a₀ + 2ⁿa₁ + 2²ⁿa₂ + ... +
 * 2ⁱⁿa_i where n is the bits of the integer architecture. The values of the polynom
 * are stored in big endian order so the array is like [a_i, ... , a₂, a₁,
 * a₀]. Additionally a sign is used in form of a signum.
 *
 * @author Stephan Schloepke
 * @since 1.0
 */
public class SignMagnitudeArrayHelper {

	/**
	 * Convert a given byte array storing a two complements big number (radix 2⁸) to an absolute magnitude
	 * stored in an int array (radix 2^{int bit length}).
	 *
	 * @param input The input in two's complement to convert (null or zero lenght array is considered to by zero and
	 *              produces a zero length integer array)
	 *
	 * @return The absolute magnitude as int array (radix 2^{int bit length})
	 *
	 * @since 1.0
	 */
	public static int[] convertFromTwoComplement(final byte[] input) {
		if (input == null || input.length == 0) {
			return ArrayConstants.ZERO_LENGTH_INT_ARRAY;
		}
		int startIndex = 0;
		boolean sign = input[0] < 0;
		if (sign) {
			while (startIndex < input.length && input[startIndex] == -1) {
				startIndex++;
			}
		} else {
			while (startIndex < input.length && input[startIndex] == 0) {
				startIndex++;
			}
		}
		// now we know the exact location of the last byte used in the two's complement
		int endIndex = input.length;
		if (endIndex - startIndex == 0) {
			return ArrayConstants.ZERO_LENGTH_INT_ARRAY;
		}
		int len = ((endIndex - startIndex) + 3)
				/ 4;
		if (sign && (len * 4) == (endIndex - startIndex)) {
			// In the case that we exactly fit into the integers we need to ensure that the borrow
			// propagation will be good so we check
			// all bytes if they are zero. Than we will need one extra int
			int i = startIndex;
			while (i < endIndex && input[i++] == 0) {
				// Nothing to do here
			}
			if (i == endIndex) {
				len++;
			}
		}
		int[] result = new int[len];
		boolean carry = true;
		for (int i = len - 1; i >= 0; i--) {
			int remaining = endIndex - startIndex;
			int tmp = 0;
			if (remaining >= 4) {
				remaining = 4;
			} else if (sign) {
				tmp = -1 << remaining * 8;
			}
			for (int bit = 0; remaining > 0; bit += 8, remaining--) {
				int t = input[--endIndex] & 0xff;
				tmp |= (t) << bit;
			}
			if (sign) {
				result[i] = ~tmp;
				if (carry) {
					carry = result[i]++ == 0;
				}
			} else {
				result[i] = tmp;
			}
		}
		return result;
	}

	/**
	 * Converts a given signum (rang [-1,1]) with a given magnitude array to a byte array two's complement number.  A
	 * zero length byte array is produced for a signum of zero indicating a zero value. 
	 *
	 * @param signum    The signum of the number to produce (-1 negtiv, 0 zero, 1 positiv).
	 * @param magnitude The absolute magnuted of the number (radix 2^{int bit length}).
	 *
	 * @return The two's complement byte array (radix 2⁸)
	 */
	public static byte[] convertToTwoComplement(final int signum, final int[] magnitude) {
		if (signum == 0 || magnitude == null || magnitude.length == 0) {
			return ArrayConstants.ZERO_LENGTH_BYTE_ARRAY;
		}
		throw new UnsupportedOperationException();
	}
}