BC1T.java

/*
 * BC1T.java
 *
 * 20th july, 2007
 * (c) 2006 EduMips64 project - Trubia Massimo
 *
 * 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.is;
import org.edumips64.core.*;
import org.edumips64.utils.*;
/**
   *<pre>
 *  Format: BC1T cc, offset
 * Description: To test an FP condition code  in the range [0,7] previously stored from c.cond.fmt instructions
 *    on the FCSR as binary value and do a PC-relative conditional branch
 *   Operation: if FCSR[cc] = 1 then branch_to_offset
 *</pre>

 */

public class BC1T extends FPConditionalBranchesInstructions {
  static String ND_FIELD = "0";
  static String TF_FIELD = "1";
  static String NAME = "BC1T";

  BC1T() {
    super.ND_FIELD = ND_FIELD;
    super.TF_FIELD = TF_FIELD;
    super.name = NAME;
  }

  public void ID() throws RAWException, IrregularWriteOperationException, IrregularStringOfBitsException, TwosComplementSumException, JumpException {
    boolean condition = (cpu.getFCSRConditionCode(params.get(CC_FIELD)) == 1) ? true : false;

    //converting offset into a signed binary value of 64 bits in length
    BitSet64 bs = new BitSet64();
    bs.writeHalf(params.get(OFFSET_FIELD));
    String offset = bs.getBinString();

    if (condition) {
      String pc_new = "";
      Register pc = cpu.getPC();
      String pc_old = cpu.getPC().getBinString();

      //subtracting 4 to the pc_old temporary variable using bitset64 safe methods
      BitSet64 bs_temp = new BitSet64();
      bs_temp.writeDoubleWord(-4);
      pc_old = InstructionsUtils.twosComplementSum(pc_old, bs_temp.getBinString());

      //updating program counter
      pc_new = InstructionsUtils.twosComplementSum(pc_old, offset);
      pc.setBits(pc_new, 0);

      throw new JumpException();
    }
  }


}