DIV.java

/** DIV.java
 *
 * 18th may 2007
 * Instruction DIV 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: DIV rs, rt
 * Description: (LO, HI) = rs / rt
 *              To divide 32-bit signed integers
 *              The 32-bit word in GPR rs is divided by the 32-bit
 *              word in GPR rt, treating both operands as signed values.
 *              The 32-bit quotient is sign-extended and placed into special register LO and the 32-bit remainder is sign-extended and
 *    placed into special register HI
 *              No arithmetic exception occurs under any circumstances.
 *</pre>


 * @author Giorgio Scibilia - Erik Urzi'- Sciuto Lorenzo
 */
class DIV extends ALU_RType {
  final static int RS_FIELD = 0;
  final static int RT_FIELD = 1;
  final static int LO_REG = 2;
  final static int HI_REG = 3;
  final String OPCODE_VALUE = "011010";

  DIV() {
    super.OPCODE_VALUE = OPCODE_VALUE;
    syntax = "%R,%R";
    name = "DIV";
  }
  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 registers (quozient and remainder)
    cpu.getLO().incrWriteSemaphore();
    cpu.getHI().incrWriteSemaphore();

  }
  public void EX() throws IrregularStringOfBitsException, IntegerOverflowException, TwosComplementSumException, DivisionByZeroException {
    //getting String from temporary register
    String rt = TR[RT_FIELD].getBinString();
    String rs = TR[RS_FIELD].getBinString();
    //cutting the high part of registers
    rt = rt.substring(32, 64);
    rs = rs.substring(32, 64);
    long l_rt = Converter.binToLong(rt, false);
    long l_rs = Converter.binToLong(rs, false);
    //performing operations
    long quotient = 0;

    try {
      quotient = l_rs / l_rt;
    } catch (ArithmeticException e) {
      if (cpu.isEnableForwarding()) {
        cpu.getLO().decrWriteSemaphore();
        cpu.getHI().decrWriteSemaphore();
      }

      throw new DivisionByZeroException();
    }

    long remainder = l_rs % l_rt;

    String str_quotient = Long.toString(quotient, 2);
    String str_remainder = Long.toString(remainder, 2);

    //performing sign extension
    if (str_quotient.charAt(0) == '-') {
      str_quotient = str_quotient.substring(1);

      for (int i = str_quotient.length(); i < 32; i++) {
        str_quotient = '0' + str_quotient;
      }

      str_quotient = Converter.twoComplement(str_quotient);
    } else
      for (int i = str_quotient.length(); i < 32; i++) {
        str_quotient = '0' + str_quotient;
      }

    if (str_remainder.charAt(0) == '-') {
      str_remainder = str_remainder.substring(1);

      for (int i = str_remainder.length(); i < 32; i++) {
        str_remainder = '0' + str_remainder;
      }

      str_remainder = Converter.twoComplement(str_remainder);
    } else
      for (int i = str_remainder.length(); i < 32; i++) {
        str_remainder = '0' + str_remainder;
      }

    for (int i = 0; i < 32; i++) {
      str_quotient = str_quotient.charAt(0) + str_quotient;
      str_remainder = str_remainder.charAt(0) + str_remainder;
    }


    //writing result in temporary registers
    //the result will never have more than 32-bits
    TR[LO_REG].setBits(str_quotient, 0);
    TR[HI_REG].setBits(str_remainder, 0);

    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(TR[LO_REG].getBinString(), 0);
    hi.setBits(TR[HI_REG].getBinString(), 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);
  }
}