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      1 /*
      2  * Copyright (c) 2003, 2013, Oracle and/or its affiliates. All rights reserved.
      3  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
      4  *
      5  * This code is free software; you can redistribute it and/or modify it
      6  * under the terms of the GNU General Public License version 2 only, as
      7  * published by the Free Software Foundation.  Oracle designates this
      8  * particular file as subject to the "Classpath" exception as provided
      9  * by Oracle in the LICENSE file that accompanied this code.
     10  *
     11  * This code is distributed in the hope that it will be useful, but WITHOUT
     12  * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
     13  * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
     14  * version 2 for more details (a copy is included in the LICENSE file that
     15  * accompanied this code).
     16  *
     17  * You should have received a copy of the GNU General Public License version
     18  * 2 along with this work; if not, write to the Free Software Foundation,
     19  * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
     20  *
     21  * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
     22  * or visit www.oracle.com if you need additional information or have any
     23  * questions.
     24  */
     25 package java.security.spec;
     26 
     27 import java.math.BigInteger;
     28 
     29 /**
     30  * This immutable class represents a point on an elliptic curve (EC)
     31  * in affine coordinates. Other coordinate systems can
     32  * extend this class to represent this point in other
     33  * coordinates.
     34  *
     35  * @author Valerie Peng
     36  *
     37  * @since 1.5
     38  */
     39 public class ECPoint {
     40 
     41     private final BigInteger x;
     42     private final BigInteger y;
     43 
     44     /**
     45      * This defines the point at infinity.
     46      */
     47     public static final ECPoint POINT_INFINITY = new ECPoint();
     48 
     49     // private constructor for constructing point at infinity
     50     private ECPoint() {
     51         this.x = null;
     52         this.y = null;
     53     }
     54 
     55     /**
     56      * Creates an ECPoint from the specified affine x-coordinate
     57      * {@code x} and affine y-coordinate {@code y}.
     58      * @param x the affine x-coordinate.
     59      * @param y the affine y-coordinate.
     60      * @exception NullPointerException if {@code x} or
     61      * {@code y} is null.
     62      */
     63     public ECPoint(BigInteger x, BigInteger y) {
     64         if ((x==null) || (y==null)) {
     65             throw new NullPointerException("affine coordinate x or y is null");
     66         }
     67         this.x = x;
     68         this.y = y;
     69     }
     70 
     71     /**
     72      * Returns the affine x-coordinate {@code x}.
     73      * Note: POINT_INFINITY has a null affine x-coordinate.
     74      * @return the affine x-coordinate.
     75      */
     76     public BigInteger getAffineX() {
     77         return x;
     78     }
     79 
     80     /**
     81      * Returns the affine y-coordinate {@code y}.
     82      * Note: POINT_INFINITY has a null affine y-coordinate.
     83      * @return the affine y-coordinate.
     84      */
     85     public BigInteger getAffineY() {
     86         return y;
     87     }
     88 
     89     /**
     90      * Compares this elliptic curve point for equality with
     91      * the specified object.
     92      * @param obj the object to be compared.
     93      * @return true if {@code obj} is an instance of
     94      * ECPoint and the affine coordinates match, false otherwise.
     95      */
     96     public boolean equals(Object obj) {
     97         if (this == obj) return true;
     98         if (this == POINT_INFINITY) return false;
     99         if (obj instanceof ECPoint) {
    100             return ((x.equals(((ECPoint)obj).x)) &&
    101                     (y.equals(((ECPoint)obj).y)));
    102         }
    103         return false;
    104     }
    105 
    106     /**
    107      * Returns a hash code value for this elliptic curve point.
    108      * @return a hash code value.
    109      */
    110     public int hashCode() {
    111         if (this == POINT_INFINITY) return 0;
    112         return x.hashCode() << 5 + y.hashCode();
    113     }
    114 }
    115