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1   /*
2    * Copyright (c) 1997, 2006, 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  
26  package sun.security.util;
27  
28  import java.io.ByteArrayOutputStream;
29  import java.util.Arrays;
30  
31  /**
32   * A packed array of booleans.
33   *
34   * @author Joshua Bloch
35   * @author Douglas Hoover
36   */
37  
38  public class BitArray {
39  
40      private byte[] repn;
41      private int length;
42  
43      private static final int BITS_PER_UNIT = 8;
44  
45      private static int subscript(int idx) {
46          return idx / BITS_PER_UNIT;
47      }
48  
49      private static int position(int idx) { // bits big-endian in each unit
50          return 1 << (BITS_PER_UNIT - 1 - (idx % BITS_PER_UNIT));
51      }
52  
53      /**
54       * Creates a BitArray of the specified size, initialized to zeros.
55       */
56      public BitArray(int length) throws IllegalArgumentException {
57          if (length < 0) {
58              throw new IllegalArgumentException("Negative length for BitArray");
59          }
60  
61          this.length = length;
62  
63          repn = new byte[(length + BITS_PER_UNIT - 1)/BITS_PER_UNIT];
64      }
65  
66  
67      /**
68       * Creates a BitArray of the specified size, initialized from the
69       * specified byte array.  The most significant bit of a[0] gets
70       * index zero in the BitArray.  The array a must be large enough
71       * to specify a value for every bit in the BitArray.  In other words,
72       * 8*a.length <= length.
73       */
74      public BitArray(int length, byte[] a) throws IllegalArgumentException {
75  
76          if (length < 0) {
77              throw new IllegalArgumentException("Negative length for BitArray");
78          }
79          if (a.length * BITS_PER_UNIT < length) {
80              throw new IllegalArgumentException("Byte array too short to represent " +
81                                                 "bit array of given length");
82          }
83  
84          this.length = length;
85  
86          int repLength = ((length + BITS_PER_UNIT - 1)/BITS_PER_UNIT);
87          int unusedBits = repLength*BITS_PER_UNIT - length;
88          byte bitMask = (byte) (0xFF << unusedBits);
89  
90          /*
91           normalize the representation:
92            1. discard extra bytes
93            2. zero out extra bits in the last byte
94           */
95          repn = new byte[repLength];
96          System.arraycopy(a, 0, repn, 0, repLength);
97          if (repLength > 0) {
98              repn[repLength - 1] &= bitMask;
99          }
100     }
101 
102     /**
103      * Create a BitArray whose bits are those of the given array
104      * of Booleans.
105      */
106     public BitArray(boolean[] bits) {
107         length = bits.length;
108         repn = new byte[(length + 7)/8];
109 
110         for (int i=0; i < length; i++) {
111             set(i, bits[i]);
112         }
113     }
114 
115 
116     /**
117      *  Copy constructor (for cloning).
118      */
119     private BitArray(BitArray ba) {
120         length = ba.length;
121         repn = ba.repn.clone();
122     }
123 
124     /**
125      *  Returns the indexed bit in this BitArray.
126      */
127     public boolean get(int index) throws ArrayIndexOutOfBoundsException {
128         if (index < 0 || index >= length) {
129             throw new ArrayIndexOutOfBoundsException(Integer.toString(index));
130         }
131 
132         return (repn[subscript(index)] & position(index)) != 0;
133     }
134 
135     /**
136      *  Sets the indexed bit in this BitArray.
137      */
138     public void set(int index, boolean value)
139     throws ArrayIndexOutOfBoundsException {
140         if (index < 0 || index >= length) {
141             throw new ArrayIndexOutOfBoundsException(Integer.toString(index));
142         }
143         int idx = subscript(index);
144         int bit = position(index);
145 
146         if (value) {
147             repn[idx] |= bit;
148         } else {
149             repn[idx] &= ~bit;
150         }
151     }
152 
153     /**
154      * Returns the length of this BitArray.
155      */
156     public int length() {
157         return length;
158     }
159 
160     /**
161      * Returns a Byte array containing the contents of this BitArray.
162      * The bit stored at index zero in this BitArray will be copied
163      * into the most significant bit of the zeroth element of the
164      * returned byte array.  The last byte of the returned byte array
165      * will be contain zeros in any bits that do not have corresponding
166      * bits in the BitArray.  (This matters only if the BitArray's size
167      * is not a multiple of 8.)
168      */
169     public byte[] toByteArray() {
170         return repn.clone();
171     }
172 
173     public boolean equals(Object obj) {
174         if (obj == this) return true;
175         if (obj == null || !(obj instanceof BitArray)) return false;
176 
177         BitArray ba = (BitArray) obj;
178 
179         if (ba.length != length) return false;
180 
181         for (int i = 0; i < repn.length; i += 1) {
182             if (repn[i] != ba.repn[i]) return false;
183         }
184         return true;
185     }
186 
187     /**
188      * Return a boolean array with the same bit values a this BitArray.
189      */
190     public boolean[] toBooleanArray() {
191         boolean[] bits = new boolean[length];
192 
193         for (int i=0; i < length; i++) {
194             bits[i] = get(i);
195         }
196         return bits;
197     }
198 
199     /**
200      * Returns a hash code value for this bit array.
201      *
202      * @return  a hash code value for this bit array.
203      */
204     public int hashCode() {
205         int hashCode = 0;
206 
207         for (int i = 0; i < repn.length; i++)
208             hashCode = 31*hashCode + repn[i];
209 
210         return hashCode ^ length;
211     }
212 
213 
214     public Object clone() {
215         return new BitArray(this);
216     }
217 
218 
219     private static final byte[][] NYBBLE = {
220         { (byte)'0',(byte)'0',(byte)'0',(byte)'0'},
221         { (byte)'0',(byte)'0',(byte)'0',(byte)'1'},
222         { (byte)'0',(byte)'0',(byte)'1',(byte)'0'},
223         { (byte)'0',(byte)'0',(byte)'1',(byte)'1'},
224         { (byte)'0',(byte)'1',(byte)'0',(byte)'0'},
225         { (byte)'0',(byte)'1',(byte)'0',(byte)'1'},
226         { (byte)'0',(byte)'1',(byte)'1',(byte)'0'},
227         { (byte)'0',(byte)'1',(byte)'1',(byte)'1'},
228         { (byte)'1',(byte)'0',(byte)'0',(byte)'0'},
229         { (byte)'1',(byte)'0',(byte)'0',(byte)'1'},
230         { (byte)'1',(byte)'0',(byte)'1',(byte)'0'},
231         { (byte)'1',(byte)'0',(byte)'1',(byte)'1'},
232         { (byte)'1',(byte)'1',(byte)'0',(byte)'0'},
233         { (byte)'1',(byte)'1',(byte)'0',(byte)'1'},
234         { (byte)'1',(byte)'1',(byte)'1',(byte)'0'},
235         { (byte)'1',(byte)'1',(byte)'1',(byte)'1'}
236     };
237 
238     private static final int BYTES_PER_LINE = 8;
239 
240     /**
241      *  Returns a string representation of this BitArray.
242      */
243     public String toString() {
244         ByteArrayOutputStream out = new ByteArrayOutputStream();
245 
246         for (int i = 0; i < repn.length - 1; i++) {
247             out.write(NYBBLE[(repn[i] >> 4) & 0x0F], 0, 4);
248             out.write(NYBBLE[repn[i] & 0x0F], 0, 4);
249 
250             if (i % BYTES_PER_LINE == BYTES_PER_LINE - 1) {
251                 out.write('\n');
252             } else {
253                 out.write(' ');
254             }
255         }
256 
257         // in last byte of repn, use only the valid bits
258         for (int i = BITS_PER_UNIT * (repn.length - 1); i < length; i++) {
259             out.write(get(i) ? '1' : '0');
260         }
261 
262         return new String(out.toByteArray());
263 
264     }
265 
266     public BitArray truncate() {
267         for (int i=length-1; i>=0; i--) {
268             if (get(i)) {
269                 return new BitArray(i+1, Arrays.copyOf(repn, (i + BITS_PER_UNIT)/BITS_PER_UNIT));
270             }
271         }
272         return new BitArray(1);
273     }
274 
275 }