MULT.java

/*
 * MULT.java
 *
 * 18th may 2007
 * Instruction MULT of the MIPS64 Instruction Set
 * (c) 2006 EduMips64 project - Giorgio Scibilia - Erik Urzi'- Sciuto Lorenzo
 *
 * 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.*;


//per diagnostica


/**
 * <pre>
 *      Syntax: MULT rs, rt
 * Description: (LO,HI) = rs * rt
 *              To multiply 32-bit signed integers
 *              The 32-bit word value in GPR rt is multiplied by the 32-bit
 *              value in GPR rs, treating both operands as signed values.
 *    The low-order 32-bit word of the result is sign-extended and placed into special register
 *    LO, and the high-order 32-bit word is sign-extended and placed into special register HI.
 * </pre>
 *
 * @author Giorgio Scibilia - Erik Urzi'- Sciuto Lorenzo
 */
class MULT extends ALU_RType {
  final int RS_FIELD = 0;
  final int RT_FIELD = 1;
  final String OPCODE_VALUE = "011000";

  String lo;
  String hi;

  MULT() {
    super.OPCODE_VALUE = OPCODE_VALUE;
    syntax = "%R,%R";
    name = "MULT";
  }
  public void ID() throws RAWException, IrregularWriteOperationException, IrregularStringOfBitsException {
    //if source registers are valid passing their own values into temporary registers
    Register rs = cpu.getRegister(params.get(RS_FIELD));
    Register rt = cpu.getRegister(params.get(RT_FIELD));

    if (rs.getWriteSemaphore() > 0 || rt.getWriteSemaphore() > 0) {
      throw new RAWException();
    }

    TR[RS_FIELD] = rs;
    TR[RT_FIELD] = rt;
    //locking the destination register

    cpu.getLO().incrWriteSemaphore();
    cpu.getHI().incrWriteSemaphore();
  }


  public void EX() throws IrregularStringOfBitsException, IntegerOverflowException, TwosComplementSumException {
    //getting registers' values and cutting the first 32-bits
    String str_rs = TR[RS_FIELD].getBinString();
    String str_rt = TR[RT_FIELD].getBinString();
    //cutting the high part of registers
    str_rs = str_rs.substring(32, 64);
    str_rt = str_rt.substring(32, 64);

    long rs = Converter.binToLong(str_rs, false);
    long rt = Converter.binToLong(str_rt, false);
    long result = rs * rt;

    //converting result to a String of 64-bit
    String tmp = Long.toString(result, 2);
    char first = '0';

    if (tmp.charAt(0) == '-') {
      first = '1';
      tmp = tmp.substring(1);
      tmp = Converter.twoComplement(tmp);
    }

    for (int i = tmp.length(); i < 64; i++) {
      tmp = first + tmp;
    }

    hi = tmp.substring(0, 32);
    lo = tmp.substring(32);

    //performing sign extension
    for (int i = 0; i < 32; i++) {
      hi = hi.charAt(0) + hi;
      lo = lo.charAt(0) + lo;
    }

    if (cpu.isEnableForwarding()) {
      doWB();
    }
  }


  public void WB() throws IrregularStringOfBitsException {
    if (!cpu.isEnableForwarding()) {
      doWB();
    }
  }
  public void doWB() throws IrregularStringOfBitsException {
    //passing results from temporary registers to destination registers and unlocking them
    Register lo = cpu.getLO();
    Register hi = cpu.getHI();
    lo.setBits(this.lo, 0);
    hi.setBits(this.hi, 0);

    lo.decrWriteSemaphore();
    hi.decrWriteSemaphore();
  }
  public void pack() throws IrregularStringOfBitsException {
    //conversion of instruction parameters of "params" list to the "repr" form (32 binary value)
    repr.setBits(OPCODE_VALUE, OPCODE_VALUE_INIT);
    repr.setBits(Converter.intToBin(RS_FIELD_LENGTH, params.get(RS_FIELD)), RS_FIELD_INIT);
    repr.setBits(Converter.intToBin(RT_FIELD_LENGTH, params.get(RT_FIELD)), RT_FIELD_INIT);
  }


}