Source for gnu.java.security.der.BitString

   1: /* BitString.java -- Java representation of the BIT STRING type.
   2:    Copyright (C) 2003 Free Software Foundation, Inc.
   3: 
   4: This file is part of GNU Classpath.
   5: 
   6: GNU Classpath is free software; you can redistribute it and/or modify
   7: it under the terms of the GNU General Public License as published by
   8: the Free Software Foundation; either version 2, or (at your option)
   9: any later version.
  10: 
  11: GNU Classpath is distributed in the hope that it will be useful, but
  12: WITHOUT ANY WARRANTY; without even the implied warranty of
  13: MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  14: General Public License for more details.
  15: 
  16: You should have received a copy of the GNU General Public License
  17: along with GNU Classpath; see the file COPYING.  If not, write to the
  18: Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
  19: 02110-1301 USA.
  20: 
  21: Linking this library statically or dynamically with other modules is
  22: making a combined work based on this library.  Thus, the terms and
  23: conditions of the GNU General Public License cover the whole
  24: combination.
  25: 
  26: As a special exception, the copyright holders of this library give you
  27: permission to link this library with independent modules to produce an
  28: executable, regardless of the license terms of these independent
  29: modules, and to copy and distribute the resulting executable under
  30: terms of your choice, provided that you also meet, for each linked
  31: independent module, the terms and conditions of the license of that
  32: module.  An independent module is a module which is not derived from
  33: or based on this library.  If you modify this library, you may extend
  34: this exception to your version of the library, but you are not
  35: obligated to do so.  If you do not wish to do so, delete this
  36: exception statement from your version. */
  37: 
  38: 
  39: package gnu.java.security.der;
  40: 
  41: import gnu.java.lang.CPStringBuilder;
  42: 
  43: import java.math.BigInteger;
  44: import java.util.Arrays;
  45: 
  46: /**
  47:  * Immutable representation of a bit string, which is equivalent to a
  48:  * byte array except some number of the rightmost bits are ignored. For
  49:  * example, this could be the bit string:
  50:  *
  51:  * <pre>   00010101 11101101 11010xxx</pre>
  52:  *
  53:  * <p>Where the "xxx" represents three bits that should be ignored, and
  54:  * can have any value.
  55:  *
  56:  * @author Casey Marshall (csm@gnu.org)
  57:  */
  58: public class BitString implements Cloneable, Comparable
  59: {
  60: 
  61:   // Fields.
  62:   // ------------------------------------------------------------------------
  63: 
  64:   /** The bits themselves. */
  65:   private final byte[] bytes;
  66: 
  67:   /**
  68:    * The exportable byte array. This array has the ignored bits
  69:    * removed.
  70:    */
  71:   private transient byte[] externBytes;
  72: 
  73:   /** The number of bits ignored at the end of the byte array. */
  74:   private final int ignoredBits;
  75: 
  76:   /** This bit string as a boolean array. */
  77:   private transient boolean[] boolVal;
  78: 
  79:   // Constructors.
  80:   // ------------------------------------------------------------------------
  81: 
  82:   /**
  83:    * Create a new bit string, shifting the given byte array if needed.
  84:    *
  85:    * @param bytes The byte array holding the bit string.
  86:    * @param ignoredBits The number of bits to ignore.
  87:    * @param doShift Pass true in this parameter if the byte array has
  88:    * not yet been shifted left by <i>ignoredBits</i>.
  89:    * @throws IllegalArgumentException If <i>ignoredBits</i> is negative
  90:    * or greater than 7.
  91:    * @throws NullPointerException If <i>bytes</i> is null.
  92:    */
  93:   public BitString(byte[] bytes, int ignoredBits, boolean doShift)
  94:   {
  95:     this(bytes, 0, bytes.length, ignoredBits, doShift);
  96:   }
  97: 
  98:   /**
  99:    * Create a new bit string, shifting the given byte array if needed.
 100:    *
 101:    * @param bytes The byte array holding the bit string.
 102:    * @param offset The offset where the meaningful bytes begin.
 103:    * @param length The number of meaningful bytes.
 104:    * @param ignoredBits The number of bits to ignore.
 105:    * @param doShift Pass true in this parameter if the byte array has
 106:    * not yet been shifted left by <i>ignoredBits</i>.
 107:    * @throws IllegalArgumentException If <i>ignoredBits</i> is negative
 108:    * or greater than 7.
 109:    * @throws NullPointerException If <i>bytes</i> is null.
 110:    */
 111:   public BitString(byte[] bytes, int offset, int length,
 112:                    int ignoredBits, boolean doShift)
 113:   {
 114:     if (ignoredBits < 0 || ignoredBits > 7)
 115:       throw new IllegalArgumentException();
 116:     if (bytes == null)
 117:       throw new NullPointerException();
 118:     if (doShift && ignoredBits > 0)
 119:       {
 120:         this.externBytes = new byte[length];
 121:         System.arraycopy(bytes, offset, externBytes, 0, length);
 122:         this.bytes = new BigInteger(externBytes).shiftLeft(ignoredBits)
 123:                        .toByteArray();
 124:       }
 125:     else
 126:       {
 127:         this.bytes = new byte[length];
 128:         System.arraycopy(bytes, offset, this.bytes, 0, length);
 129:       }
 130:     this.ignoredBits = ignoredBits;
 131:   }
 132: 
 133:   /**
 134:    * Create a new bit string.
 135:    *
 136:    * @param bytes The byte array holding the bit string.
 137:    * @param offset The offset where the meaningful bytes begin.
 138:    * @param length The number of meaningful bytes.
 139:    * @param ignoredBits The number of bits to ignore.
 140:    * @throws IllegalArgumentException If <i>ignoredBits</i> is negative
 141:    * or greater than 7.
 142:    * @throws NullPointerException If <i>bytes</i> is null.
 143:    */
 144:   public BitString(byte[] bytes, int offset, int length, int ignoredBits)
 145:   {
 146:     this(bytes, offset, length, ignoredBits, false);
 147:   }
 148: 
 149:   /**
 150:    * Create a new bit string.
 151:    *
 152:    * @param bytes The byte array holding the bit string.
 153:    * @param ignoredBits The number of bits to ignore.
 154:    * @throws IllegalArgumentException If <i>ignoredBits</i> is negative
 155:    * or greater than 7.
 156:    * @throws NullPointerException If <i>bytes</i> is null.
 157:    */
 158:   public BitString(byte[] bytes, int ignoredBits)
 159:   {
 160:     this(bytes, 0, bytes.length, ignoredBits, false);
 161:   }
 162: 
 163:   /**
 164:    * Create a new bit string.
 165:    *
 166:    * @param bytes The byte array holding the bit string.
 167:    * @param offset The offset where the meaningful bytes begin.
 168:    * @param length The number of meaningful bytes.
 169:    * @throws NullPointerException If <i>bytes</i> is null.
 170:    */
 171:   public BitString(byte[] bytes, int offset, int length)
 172:   {
 173:     this(bytes, offset, length, 0, false);
 174:   }
 175: 
 176:   /**
 177:    * Create a new bit string.
 178:    *
 179:    * @param bytes The byte array holding the bit string.
 180:    * @throws NullPointerException If <i>bytes</i> is null.
 181:    */
 182:   public BitString(byte[] bytes)
 183:   {
 184:     this(bytes, 0, bytes.length, 0, false);
 185:   }
 186: 
 187:   // Instance methods.
 188:   // ------------------------------------------------------------------------
 189: 
 190:   /**
 191:    * Return this bit string as a byte array, with the ignored bits
 192:    * trimmed off. The byte array is cloned every time this method is
 193:    * called to prevent modification.
 194:    *
 195:    * @return The trimmed byte array.
 196:    */
 197:   public byte[] toByteArray()
 198:   {
 199:     if (ignoredBits == 0)
 200:       return (byte[]) bytes.clone();
 201:     if (externBytes == null)
 202:       externBytes = new BigInteger(bytes).shiftRight(ignoredBits).toByteArray();
 203:     return (byte[]) externBytes.clone();
 204:   }
 205: 
 206:   /**
 207:    * Returns this bit string as a byte array, with the ignored bits
 208:    * present. The byte array is cloned every time this method is
 209:    * called to prevent modification.
 210:    *
 211:    * @return The byte array.
 212:    */
 213:   public byte[] getShiftedByteArray()
 214:   {
 215:     return (byte[]) bytes.clone();
 216:   }
 217: 
 218:   /**
 219:    * Returns the number of ignored bits.
 220:    *
 221:    * @return The number of ignored bits.
 222:    */
 223:   public int getIgnoredBits()
 224:   {
 225:     return ignoredBits;
 226:   }
 227: 
 228:   /**
 229:    * Returns the size, in bits, of this bit string.
 230:    *
 231:    * @return The size of this bit string.
 232:    */
 233:   public int size()
 234:   {
 235:     return (bytes.length << 3) - ignoredBits;
 236:   }
 237: 
 238:   /**
 239:    * Return this bit string as a boolean array. The value returned is of
 240:    * size {@link #size()}, and each <code>true</code> value
 241:    * corresponding to each "1" in this bit string. The boolean array is
 242:    * cloned before it is returned.
 243:    *
 244:    * @return The boolean array.
 245:    */
 246:   public boolean[] toBooleanArray()
 247:   {
 248:     if (boolVal == null)
 249:       {
 250:         boolVal = new boolean[size()];
 251:         for (int i = 0, j = 7, k = 0; i < boolVal.length; i++)
 252:           {
 253:             boolVal[i] = (bytes[k] & 1 << j--) != 0;
 254:             if (j < 0)
 255:               {
 256:                 j = 7;
 257:                 k++;
 258:               }
 259:           }
 260:       }
 261:     return (boolean[]) boolVal.clone();
 262:   }
 263: 
 264:   public Object clone()
 265:   {
 266:     try
 267:       {
 268:         return super.clone();
 269:       }
 270:     catch (CloneNotSupportedException cce)
 271:       {
 272:         throw new InternalError(cce.getMessage());
 273:       }
 274:   }
 275: 
 276:   public int compareTo(Object o)
 277:   {
 278:     BitString that = (BitString) o;
 279:     if (this.equals(that))
 280:       return 0;
 281:     if (this.bytes.length != that.bytes.length)
 282:       return (this.bytes.length < that.bytes.length) ? -1 : 1;
 283:     if (this.ignoredBits != that.ignoredBits)
 284:       return (this.ignoredBits < that.ignoredBits) ? -1 : 1;
 285:     for (int i = 0; i < this.bytes.length; i++)
 286:       if (this.bytes[i] != that.bytes[i])
 287:         return (this.bytes[i] < that.bytes[i]) ? -1 : 1;
 288:     return 0; // not reached.
 289:   }
 290: 
 291:   public int hashCode()
 292:   {
 293:     int result = 0;
 294:     for (int i = 0; i < bytes.length - 1; ++i)
 295:       result = result * 31 + bytes[i];
 296:     if (bytes.length > 0)
 297:       {
 298:         int lastByte = bytes[bytes.length - 1] & ~ ((1 << ignoredBits) - 1);
 299:         result = result * 31 + lastByte;
 300:       }
 301:     return result;
 302:   }
 303: 
 304:   public boolean equals(Object o)
 305:   {
 306:     if (!(o instanceof BitString))
 307:       return false;
 308:     BitString that = (BitString) o;
 309:     // True for cloned instances.
 310:     if (this.bytes == that.bytes && this.ignoredBits == that.ignoredBits)
 311:       return true;
 312:     if (this.ignoredBits == that.ignoredBits)
 313:       return Arrays.equals(this.bytes, that.bytes);
 314:     return false;
 315:   }
 316: 
 317:   public String toString()
 318:   {
 319:     CPStringBuilder sb = new CPStringBuilder();
 320:     for (int i = 0, j = 7, k = 0; i < size(); i++)
 321:       {
 322:         sb.append((bytes[k] & 1 << j) != 0 ? "1" : "0");
 323:         j--;
 324:         if (j < 0)
 325:           {
 326:             j = 7;
 327:             k++;
 328:           }
 329:       }
 330:     return sb.toString();
 331:   }
 332: }