FixedBitSet.java

/* FixedBitSet.java
 *
 * Abstract class, used for the derivation of the basic data structure of
 * registers, memory, instructions.
 * (c) 2006 Salvatore Scellato
 *
 * This file is part of the EduMIPS64 project, and is released under the GNU
 * General Public License.
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation; either version 2 of the License, or
 * (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program; if not, write to the Free Software
 * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
 */
package org.edumips64.core;

import org.edumips64.utils.*;
/** Abstract class: it contains a fixed-size BitSet instance.
 * @author Salvatore Scellato
 * */
abstract class FixedBitSet {

  private char[] bitset;
  protected int size;

  /** Creates a default new instance of FixedBitSet with a given size. */
  FixedBitSet(int desiredSize) {
    size = desiredSize;
    bitset = new char[size];
    reset(false);
  }

  /** Resets this FixedBitSet, setting all bits to one if value is true and setting all bits to zero
   * if value is false
   * @param value if true bits will be set to '1', if false bits will be set to '0'
   * */
  public void reset(boolean value) {
    for (int i = 0; i < size; ++i) {
      bitset[i] = value ? '1' : '0';
    }
  }

  /** Using a string containg binary digits (bits) this method sets the bit
   * of the FixedBitSet starting from the <code>start</code> position until reaching
   * the end of the string or the end of the FixedBitSet.
   * TODO(andrea): should this raise an exception if len(bits) > this.size?
   * @param bits string made of "0" and "1" chars
   * @param start index of the first bit to be set
   * @throws IrregularStringOfBitsException if the String bits does not contain only "0" and "1" chars
   */
  public void setBits(String bits, int start) throws IrregularStringOfBitsException {
    int index;
    for (int i = 0; i < bits.length(); i++) {
      index = i + start;

      if (index >= size) {
        return;
      }

      char c = bits.charAt(i);

      switch (c) {
      case '1':
        bitset[index] = '1';
        break;
      case '0':
        bitset[index] = '0';
        break;
      default:
        throw new IrregularStringOfBitsException();
      }
    }
  }

  /** Returns the bit sequence of this FixedBitSet as a string containing "0"s and "1"s.
   * The sequence will contain all the bits in the bitset.
   * @return string form of the bit sequence stored in this FixedBitSet
   */
  public String getBinString() {
    return new String(bitset);
  }

  /** Returns the bit sequence of this FixedBitSet as a string containing hexadecimal
   * digits.
   * @return string form of the bit sequence stored in this FixedBitSet as hexadecimal digits
   * @throws IrregularStringOfBitsException if the bit sequence is not well-formed
   */
  public String getHexString() throws IrregularStringOfBitsException {
    return Converter.binToHex(this.getBinString());
  }
}