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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.arbitrary.internal;

/**
 * Internal calculation unit to use for calculation
 *
 * @author Stephan Schloepke
 */
class InternalCalculationImpl implements InternalCalculation {

	/**
	 * Adds x and y and returns the result.
	 *
	 * @param x The x array
	 * @param y The y array
	 *
	 * @return The result in a newly allocated array
	 */
	public int[] add(int[] x, int[] y) {
		if (x.length < y.length) {
			return add(y, x, 0, y.length, 0, x.length);
		}
		return add(x, y, 0, x.length, 0, y.length);
	}

	/**
	 * Required, that x is longer or equal in size to y.
	 *
	 * @param x    The x array
	 * @param y    The y array
	 * @param xoff The offset in the x array to start
	 * @param xlen The length from the offset to add
	 * @param yoff The offset in the y array to start
	 * @param ylen The length from the offset to add (must be less than or equal to xlen).
	 *
	 * @return The addition result in a newly created array
	 */
	public int[] add(int[] x, int[] y, int xoff, int xlen, int yoff, int ylen) {
		int j = ylen;
		int i = xlen;
		int xi, sum;
		int[] result = new int[xlen];
		boolean carry = false;
		while (--j >= yoff) {
			xi = x[--i];
			if (carry) {
				sum = result[i] = (xi + y[j]) + 1;
				carry = (sum >>> 1) < (xi >>> 1) || ((sum >>> 1) == (xi >>> 1) && (((sum | xi) & 0x1) != 0));
			} else {
				sum = result[i] = (xi + y[j]);
				carry = (sum >>> 1) < (xi >>> 1) || ((sum >>> 1) == (xi >>> 1) && ((xi & 0x1) != 0));
			}
		}
		// we have a carry from the iteration before. so we need to actually iterate any further
		// with x
		while (i > xoff && carry) {
			carry = (result[--i] = x[i] + 1) == 0;
		}
		// Now we are done iterating and we have to copy the remaining without carry propagation
		while (i > xoff) {
			result[--i] = x[i];
		}
		// If we had a carry propagation last and the result produced a carry we need to propagate
		// it and extend the result array
		if (carry) {
			int[] t = new int[result.length + 1];
			System.arraycopy(result, 0, t, 1, result.length);
			t[0] = 1;
			return t;
		}
		return result;
	}

	/**
	 * Subtracts y from x where x must be a number greater than y (so no underflow occurs).
	 *
	 * @param x The x array (must be a number greater than y)
	 * @param y The y array
	 *
	 * @return The result in a newly allocated array
	 */
	public int[] subtract(int[] x, int[] y) {
		return subtract(x, y, 0, x.length, 0, y.length);
	}

	/**
	 * Subtract y from x where x must be a number smaller than y (so no underflow occurs).
	 *
	 * @param x    The x array
	 * @param y    The y array
	 * @param xoff The offset to start in the x array
	 * @param xlen The length from the offset to use in the x array
	 * @param yoff The offset to start in the y array
	 * @param ylen The length from the offset to use in the y array
	 *
	 * @return The result in a newly allocated array with all leading zeros stripped
	 */
	public int[] subtract(int[] x, int[] y, int xoff, int xlen, int yoff, int ylen) {
		int[] result = new int[xlen];
		// from now we know x is the longer and y the shorter. so lets iterate over y and add
		int j = ylen;
		int i = xlen;
		int xi, sum;
		boolean carry = true;
		while (--j >= yoff) {
			xi = x[--i];
			if (carry) {
				sum = result[i] = (xi - y[j]);
				carry = (sum >>> 1) < (xi >>> 1) || ((sum >>> 1) == (xi >>> 1) && ((xi & 0x1) != 0));
			} else {
				sum = result[i] = (xi - y[j]) - 1;
				carry = (sum >>> 1) < (xi >>> 1) || ((sum >>> 1) == (xi >>> 1) && (((sum | xi) & 0x1) != 0));
			}
		}
		// we have a carry from the iteration before. so we need to actually iterate any further
		// with x
		while (i > xoff && !carry) {
			carry = (result[--i] = x[i] - 1) == 0;
		}
		// Now we are done iterating and we have to copy the remaining without carry propagation
		while (i > xoff) {
			result[--i] = x[i];
		}
// // If we had a carry propagation last and the result produced a carry we need to propagate
// // it and extend the result array
// if (!carry) {
// int[] t = new int[result.length + 1];
// System.arraycopy(result, 0, t, 1, result.length);
// t[0] = 1;
// return t;
// }
		return stripLeadingZeros(result);
	}

	public int[] multiply(int[] x, int[] y) {
		return multiply(x, y, 0, x.length, 0, y.length);
	}

	public int[] multiply(int[] x, int[] y, int xoff, int xlen, int yoff, int ylen) {
		int[] z = new int[xlen + ylen];
		int i = xlen;
		int j = ylen - 1;
		int k = z.length;
		long product = 0;
		while (i > xoff) {
			z[--k] = (int) (product = (x[--i] & LONG_32BIT_MASK) * (y[j] & LONG_32BIT_MASK) + product);
			product >>>= 32;
		}
		z[--k] = (int) product;
		while (j > yoff) {
			i = xlen;
			k = ylen + j--;
			product = 0;
			while (i > xoff) {
				z[--k] = (int) (product = (x[--i] & LONG_32BIT_MASK) * (y[j] & LONG_32BIT_MASK)
						+ (z[k] & LONG_32BIT_MASK) + product);
				product >>>= 32;
			}
			z[--k] = (int) product;
		}
		return stripLeadingZeros(z);
	}

	public int[] stripLeadingZeros(int[] x) {
		if (x.length == 0 || x[0] != 0) {
			return x;
		}
		int i = 0;
		while (i < x.length && x[i] == 0) {
			i++;
		}
		int[] result = new int[x.length - i];
		System.arraycopy(x, i, result, 0, result.length);
		return result;
	}
}