Bochs/bochs/cpu/arith16.cc

/////////////////////////////////////////////////////////////////////////
// $Id: arith16.cc,v 1.28 2002-10-25 18:26:26 sshwarts Exp $
/////////////////////////////////////////////////////////////////////////
//
//  Copyright (C) 2001  MandrakeSoft S.A.
//
//    MandrakeSoft S.A.
//    43, rue d'Aboukir
//    75002 Paris - France
//    http://www.linux-mandrake.com/
//    http://www.mandrakesoft.com/
//
//  This library is free software; you can redistribute it and/or
//  modify it under the terms of the GNU Lesser General Public
//  License as published by the Free Software Foundation; either
//  version 2 of the License, or (at your option) any later version.
//
//  This library 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
//  Lesser General Public License for more details.
//
//  You should have received a copy of the GNU Lesser General Public
//  License along with this library; if not, write to the Free Software
//  Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307 USA





#define NEED_CPU_REG_SHORTCUTS 1
#include "bochs.h"
#define LOG_THIS BX_CPU_THIS_PTR


  void
BX_CPU_C::INC_RX(bxInstruction_c *i)
{
#if (defined(__i386__) && defined(__GNUC__) && BX_SupportHostAsms)
  Bit32u flags32;

  asmInc16(BX_CPU_THIS_PTR gen_reg[i->opcodeReg()].word.rx, flags32);
  setEFlagsOSZAP(flags32);
#else
  Bit16u rx;
  rx = ++ BX_CPU_THIS_PTR gen_reg[i->opcodeReg()].word.rx;

  SET_FLAGS_OSZAP_16(0, 0, rx, BX_INSTR_INC16);
#endif
}

  void
BX_CPU_C::DEC_RX(bxInstruction_c *i)
{
#if (defined(__i386__) && defined(__GNUC__) && BX_SupportHostAsms)
  Bit32u flags32;

  asmDec16(BX_CPU_THIS_PTR gen_reg[i->opcodeReg()].word.rx, flags32);
  setEFlagsOSZAP(flags32);
#else
  Bit16u rx;

  rx = -- BX_CPU_THIS_PTR gen_reg[i->opcodeReg()].word.rx;

  SET_FLAGS_OSZAP_16(0, 0, rx, BX_INSTR_DEC16);
#endif
}


  void
BX_CPU_C::ADD_EwGw(bxInstruction_c *i)
{
  Bit16u op2_16, op1_16, sum_16;

  op2_16 = BX_READ_16BIT_REG(i->nnn());

  if (i->modC0()) {
    op1_16 = BX_READ_16BIT_REG(i->rm());
    sum_16 = op1_16 + op2_16;
    BX_WRITE_16BIT_REG(i->rm(), sum_16);
    }
  else {
    read_RMW_virtual_word(i->seg(), RMAddr(i), &op1_16);
    sum_16 = op1_16 + op2_16;
    Write_RMW_virtual_word(sum_16);
    }

  SET_FLAGS_OSZAPC_16(op1_16, op2_16, sum_16, BX_INSTR_ADD16);
}


  void
BX_CPU_C::ADD_GwEEw(bxInstruction_c *i)
{
  Bit16u op1_16, op2_16, sum_16;
  unsigned nnn = i->nnn();

  op1_16 = BX_READ_16BIT_REG(nnn);

  read_virtual_word(i->seg(), RMAddr(i), &op2_16);

#if (defined(__i386__) && defined(__GNUC__) && BX_SupportHostAsms)
  Bit32u flags32;

  asmAdd16(sum_16, op1_16, op2_16, flags32);
  setEFlagsOSZAPC(flags32);
#else
  sum_16 = op1_16 + op2_16;
#endif

  BX_WRITE_16BIT_REG(nnn, sum_16);

#if !(defined(__i386__) && defined(__GNUC__) && BX_SupportHostAsms)
  SET_FLAGS_OSZAPC_16(op1_16, op2_16, sum_16, BX_INSTR_ADD16);
#endif
}

  void
BX_CPU_C::ADD_GwEGw(bxInstruction_c *i)
{
  Bit16u op1_16, op2_16, sum_16;
  unsigned nnn = i->nnn();

  op1_16 = BX_READ_16BIT_REG(nnn);
  op2_16 = BX_READ_16BIT_REG(i->rm());

#if (defined(__i386__) && defined(__GNUC__) && BX_SupportHostAsms)
  Bit32u flags32;

  asmAdd16(sum_16, op1_16, op2_16, flags32);
  setEFlagsOSZAPC(flags32);
#else
  sum_16 = op1_16 + op2_16;
#endif

  BX_WRITE_16BIT_REG(nnn, sum_16);

#if !(defined(__i386__) && defined(__GNUC__) && BX_SupportHostAsms)
  SET_FLAGS_OSZAPC_16(op1_16, op2_16, sum_16, BX_INSTR_ADD16);
#endif
}


  void
BX_CPU_C::ADD_AXIw(bxInstruction_c *i)
{
  Bit16u op1_16, op2_16, sum_16;

  op1_16 = AX;
  op2_16 = i->Iw();

  sum_16 = op1_16 + op2_16;

  AX = sum_16;

  SET_FLAGS_OSZAPC_16(op1_16, op2_16, sum_16, BX_INSTR_ADD16);
}

  void
BX_CPU_C::ADC_EwGw(bxInstruction_c *i)
{
  bx_bool temp_CF;
  Bit16u op2_16, op1_16, sum_16;

  temp_CF = getB_CF();

  op2_16 = BX_READ_16BIT_REG(i->nnn());

  if (i->modC0()) {
    op1_16 = BX_READ_16BIT_REG(i->rm());
    sum_16 = op1_16 + op2_16 + temp_CF;
    BX_WRITE_16BIT_REG(i->rm(), sum_16);
    }
  else {
    read_RMW_virtual_word(i->seg(), RMAddr(i), &op1_16);
    sum_16 = op1_16 + op2_16 + temp_CF;
    Write_RMW_virtual_word(sum_16);
    }

  SET_FLAGS_OSZAPC_16_CF(op1_16, op2_16, sum_16, BX_INSTR_ADC16,
                         temp_CF);
}


  void
BX_CPU_C::ADC_GwEw(bxInstruction_c *i)
{
  bx_bool temp_CF;
  Bit16u op1_16, op2_16, sum_16;

  temp_CF = getB_CF();


  op1_16 = BX_READ_16BIT_REG(i->nnn());

  if (i->modC0()) {
    op2_16 = BX_READ_16BIT_REG(i->rm());
    }
  else {
    read_virtual_word(i->seg(), RMAddr(i), &op2_16);
    }

  sum_16 = op1_16 + op2_16 + temp_CF;

  BX_WRITE_16BIT_REG(i->nnn(), sum_16);

  SET_FLAGS_OSZAPC_16_CF(op1_16, op2_16, sum_16, BX_INSTR_ADC16,
                         temp_CF);
}


  void
BX_CPU_C::ADC_AXIw(bxInstruction_c *i)
{
  bx_bool temp_CF;
  Bit16u op1_16, op2_16, sum_16;

  temp_CF = getB_CF();

  op1_16 = AX;
  op2_16 = i->Iw();

  sum_16 = op1_16 + op2_16 + temp_CF;

  AX = sum_16;

  SET_FLAGS_OSZAPC_16_CF(op1_16, op2_16, sum_16, BX_INSTR_ADC16,
                         temp_CF);
}




  void
BX_CPU_C::SBB_EwGw(bxInstruction_c *i)
{
  bx_bool temp_CF;
  Bit16u op2_16, op1_16, diff_16;

  temp_CF = getB_CF();

  op2_16 = BX_READ_16BIT_REG(i->nnn());

  if (i->modC0()) {
    op1_16 = BX_READ_16BIT_REG(i->rm());
    diff_16 = op1_16 - (op2_16 + temp_CF);
    BX_WRITE_16BIT_REG(i->rm(), diff_16);
    }
  else {
    read_RMW_virtual_word(i->seg(), RMAddr(i), &op1_16);
    diff_16 = op1_16 - (op2_16 + temp_CF);
    Write_RMW_virtual_word(diff_16);
    }

  SET_FLAGS_OSZAPC_16_CF(op1_16, op2_16, diff_16, BX_INSTR_SBB16,
                         temp_CF);
}


  void
BX_CPU_C::SBB_GwEw(bxInstruction_c *i)
{
  bx_bool temp_CF;

  temp_CF = getB_CF();

  Bit16u op1_16, op2_16, diff_16;

  op1_16 = BX_READ_16BIT_REG(i->nnn());

  if (i->modC0()) {
    op2_16 = BX_READ_16BIT_REG(i->rm());
    }
  else {
    read_virtual_word(i->seg(), RMAddr(i), &op2_16);
    }

  diff_16 = op1_16 - (op2_16 + temp_CF);

  BX_WRITE_16BIT_REG(i->nnn(), diff_16);

  SET_FLAGS_OSZAPC_16_CF(op1_16, op2_16, diff_16, BX_INSTR_SBB16,
                         temp_CF);
}


  void
BX_CPU_C::SBB_AXIw(bxInstruction_c *i)
{
  bx_bool temp_CF;
  Bit16u op1_16, op2_16, diff_16;

  temp_CF = getB_CF();

  op1_16 = AX;
  op2_16 = i->Iw();

  diff_16 = op1_16 - (op2_16 + temp_CF);

  AX = diff_16;

  SET_FLAGS_OSZAPC_16_CF(op1_16, op2_16, diff_16, BX_INSTR_SBB16,
                         temp_CF);
}



  void
BX_CPU_C::SBB_EwIw(bxInstruction_c *i)
{
  bx_bool temp_CF;
  Bit16u op2_16, op1_16, diff_16;

  temp_CF = getB_CF();

  op2_16 = i->Iw();

  if (i->modC0()) {
    op1_16 = BX_READ_16BIT_REG(i->rm());
    diff_16 = op1_16 - (op2_16 + temp_CF);
    BX_WRITE_16BIT_REG(i->rm(), diff_16);
    }
  else {
    read_RMW_virtual_word(i->seg(), RMAddr(i), &op1_16);
    diff_16 = op1_16 - (op2_16 + temp_CF);
    Write_RMW_virtual_word(diff_16);
    }

  SET_FLAGS_OSZAPC_16_CF(op1_16, op2_16, diff_16, BX_INSTR_SBB16,
                         temp_CF);
}


  void
BX_CPU_C::SUB_EwGw(bxInstruction_c *i)
{
  Bit16u op2_16, op1_16, diff_16;

  op2_16 = BX_READ_16BIT_REG(i->nnn());

  if (i->modC0()) {
    op1_16 = BX_READ_16BIT_REG(i->rm());
#if (defined(__i386__) && defined(__GNUC__) && BX_SupportHostAsms)
    Bit32u flags32;

    asmSub16(diff_16, op1_16, op2_16, flags32);
    setEFlagsOSZAPC(flags32);
#else
    diff_16 = op1_16 - op2_16;
#endif
    BX_WRITE_16BIT_REG(i->rm(), diff_16);
    }
  else {
    read_RMW_virtual_word(i->seg(), RMAddr(i), &op1_16);
#if (defined(__i386__) && defined(__GNUC__) && BX_SupportHostAsms)
    Bit32u flags32;

    asmSub16(diff_16, op1_16, op2_16, flags32);
    setEFlagsOSZAPC(flags32);
#else
    diff_16 = op1_16 - op2_16;
#endif
    Write_RMW_virtual_word(diff_16);
    }

#if !(defined(__i386__) && defined(__GNUC__) && BX_SupportHostAsms)
  SET_FLAGS_OSZAPC_16(op1_16, op2_16, diff_16, BX_INSTR_SUB16);
#endif
}


  void
BX_CPU_C::SUB_GwEw(bxInstruction_c *i)
{
  Bit16u op1_16, op2_16, diff_16;
  unsigned nnn = i->nnn();

  op1_16 = BX_READ_16BIT_REG(nnn);

  if (i->modC0()) {
    op2_16 = BX_READ_16BIT_REG(i->rm());
    }
  else {
    read_virtual_word(i->seg(), RMAddr(i), &op2_16);
    }

#if (defined(__i386__) && defined(__GNUC__) && BX_SupportHostAsms)
  Bit32u flags32;

  asmSub16(diff_16, op1_16, op2_16, flags32);
  setEFlagsOSZAPC(flags32);
#else
  diff_16 = op1_16 - op2_16;
#endif

  BX_WRITE_16BIT_REG(nnn, diff_16);

#if !(defined(__i386__) && defined(__GNUC__) && BX_SupportHostAsms)
  SET_FLAGS_OSZAPC_16(op1_16, op2_16, diff_16, BX_INSTR_SUB16);
#endif
}

  void
BX_CPU_C::SUB_AXIw(bxInstruction_c *i)
{
  Bit16u op1_16, op2_16, diff_16;

  op1_16 = AX;
  op2_16 = i->Iw();

#if (defined(__i386__) && defined(__GNUC__) && BX_SupportHostAsms)
  Bit32u flags32;

  asmSub16(diff_16, op1_16, op2_16, flags32);
  setEFlagsOSZAPC(flags32);
#else
  diff_16 = op1_16 - op2_16;
#endif

  AX = diff_16;

#if !(defined(__i386__) && defined(__GNUC__) && BX_SupportHostAsms)
  SET_FLAGS_OSZAPC_16(op1_16, op2_16, diff_16, BX_INSTR_SUB16);
#endif
}


  void
BX_CPU_C::CMP_EwGw(bxInstruction_c *i)
{
  Bit16u op2_16, op1_16;

  op2_16 = BX_READ_16BIT_REG(i->nnn());

  if (i->modC0()) {
    op1_16 = BX_READ_16BIT_REG(i->rm());
    }
  else {
    read_virtual_word(i->seg(), RMAddr(i), &op1_16);
    }

#if (defined(__i386__) && defined(__GNUC__) && BX_SupportHostAsms)
  Bit32u flags32;

  asmCmp16(op1_16, op2_16, flags32);
  setEFlagsOSZAPC(flags32);
#else
  Bit16u diff_16;
  diff_16 = op1_16 - op2_16;

  SET_FLAGS_OSZAPC_16(op1_16, op2_16, diff_16, BX_INSTR_CMP16);
#endif
}


  void
BX_CPU_C::CMP_GwEw(bxInstruction_c *i)
{
  Bit16u op1_16, op2_16;

  op1_16 = BX_READ_16BIT_REG(i->nnn());

  if (i->modC0()) {
    op2_16 = BX_READ_16BIT_REG(i->rm());
    }
  else {
    read_virtual_word(i->seg(), RMAddr(i), &op2_16);
    }

#if (defined(__i386__) && defined(__GNUC__) && BX_SupportHostAsms)
  Bit32u flags32;

  asmCmp16(op1_16, op2_16, flags32);
  setEFlagsOSZAPC(flags32);
#else
  Bit16u diff_16;
  diff_16 = op1_16 - op2_16;

  SET_FLAGS_OSZAPC_16(op1_16, op2_16, diff_16, BX_INSTR_CMP16);
#endif
}


  void
BX_CPU_C::CMP_AXIw(bxInstruction_c *i)
{
  Bit16u op1_16, op2_16;

  op1_16 = AX;
  op2_16 = i->Iw();

#if (defined(__i386__) && defined(__GNUC__) && BX_SupportHostAsms)
  Bit32u flags32;

  asmCmp16(op1_16, op2_16, flags32);
  setEFlagsOSZAPC(flags32);
#else
  Bit16u diff_16;
  diff_16 = op1_16 - op2_16;

  SET_FLAGS_OSZAPC_16(op1_16, op2_16, diff_16, BX_INSTR_CMP16);
#endif
}


  void
BX_CPU_C::CBW(bxInstruction_c *i)
{
  /* CBW: no flags are effected */

  AX = (Bit8s) AL;
}

  void
BX_CPU_C::CWD(bxInstruction_c *i)
{
  /* CWD: no flags are affected */

  if (AX & 0x8000) {
    DX = 0xFFFF;
    }
  else {
    DX = 0x0000;
    }
}


  void
BX_CPU_C::XADD_EwGw(bxInstruction_c *i)
{
#if (BX_CPU_LEVEL >= 4) || (BX_CPU_LEVEL_HACKED >= 4)

  Bit16u op2_16, op1_16, sum_16;

  /* XADD dst(r/m), src(r)
   * temp <-- src + dst         | sum = op2 + op1
   * src  <-- dst               | op2 = op1
   * dst  <-- tmp               | op1 = sum
   */

  op2_16 = BX_READ_16BIT_REG(i->nnn());

  if (i->modC0()) {
    op1_16 = BX_READ_16BIT_REG(i->rm());
    sum_16 = op1_16 + op2_16;
    // and write destination into source
    // Note: if both op1 & op2 are registers, the last one written
    //       should be the sum, as op1 & op2 may be the same register.
    //       For example:  XADD AL, AL
    BX_WRITE_16BIT_REG(i->nnn(), op1_16);
    BX_WRITE_16BIT_REG(i->rm(), sum_16);
    }
  else {
    read_RMW_virtual_word(i->seg(), RMAddr(i), &op1_16);
    sum_16 = op1_16 + op2_16;
    Write_RMW_virtual_word(sum_16);
    /* and write destination into source */
    BX_WRITE_16BIT_REG(i->nnn(), op1_16);
    }

  SET_FLAGS_OSZAPC_16(op1_16, op2_16, sum_16, BX_INSTR_XADD16);
#else
  BX_PANIC(("XADD_EvGv: not supported on < 80486"));
#endif
}



  void
BX_CPU_C::ADD_EEwIw(bxInstruction_c *i)
{
  Bit16u op2_16, op1_16, sum_16;

  op2_16 = i->Iw();

  read_RMW_virtual_word(i->seg(), RMAddr(i), &op1_16);

#if (defined(__i386__) && defined(__GNUC__) && BX_SupportHostAsms)
  Bit32u flags32;

  asmAdd16(sum_16, op1_16, op2_16, flags32);
  setEFlagsOSZAPC(flags32);
#else
  sum_16 = op1_16 + op2_16;
#endif
  Write_RMW_virtual_word(sum_16);

#if !(defined(__i386__) && defined(__GNUC__) && BX_SupportHostAsms)
  SET_FLAGS_OSZAPC_16(op1_16, op2_16, sum_16, BX_INSTR_ADD16);
#endif
}

  void
BX_CPU_C::ADD_EGwIw(bxInstruction_c *i)
{
  Bit16u op2_16, op1_16, sum_16;

  op2_16 = i->Iw();

  op1_16 = BX_READ_16BIT_REG(i->rm());

#if (defined(__i386__) && defined(__GNUC__) && BX_SupportHostAsms)
  Bit32u flags32;

  asmAdd16(sum_16, op1_16, op2_16, flags32);
  setEFlagsOSZAPC(flags32);
#else
  sum_16 = op1_16 + op2_16;
#endif
  BX_WRITE_16BIT_REG(i->rm(), sum_16);

#if !(defined(__i386__) && defined(__GNUC__) && BX_SupportHostAsms)
  SET_FLAGS_OSZAPC_16(op1_16, op2_16, sum_16, BX_INSTR_ADD16);
#endif
}

  void
BX_CPU_C::ADC_EwIw(bxInstruction_c *i)
{
  bx_bool temp_CF;
  Bit16u op2_16, op1_16, sum_16;

  temp_CF = getB_CF();

  op2_16 = i->Iw();

  if (i->modC0()) {
    op1_16 = BX_READ_16BIT_REG(i->rm());
    sum_16 = op1_16 + op2_16 + temp_CF;
    BX_WRITE_16BIT_REG(i->rm(), sum_16);
    }
  else {
    read_RMW_virtual_word(i->seg(), RMAddr(i), &op1_16);
    sum_16 = op1_16 + op2_16 + temp_CF;
    Write_RMW_virtual_word(sum_16);
    }

  SET_FLAGS_OSZAPC_16_CF(op1_16, op2_16, sum_16, BX_INSTR_ADC16,
                         temp_CF);
}


  void
BX_CPU_C::SUB_EwIw(bxInstruction_c *i)
{
  Bit16u op2_16, op1_16, diff_16;


  op2_16 = i->Iw();

  if (i->modC0()) {
    op1_16 = BX_READ_16BIT_REG(i->rm());
#if (defined(__i386__) && defined(__GNUC__) && BX_SupportHostAsms)
    Bit32u flags32;

    asmSub16(diff_16, op1_16, op2_16, flags32);
    setEFlagsOSZAPC(flags32);
#else
    diff_16 = op1_16 - op2_16;
#endif
    BX_WRITE_16BIT_REG(i->rm(), diff_16);
    }
  else {
    read_RMW_virtual_word(i->seg(), RMAddr(i), &op1_16);
#if (defined(__i386__) && defined(__GNUC__) && BX_SupportHostAsms)
    Bit32u flags32;

    asmSub16(diff_16, op1_16, op2_16, flags32);
    setEFlagsOSZAPC(flags32);
#else
    diff_16 = op1_16 - op2_16;
#endif
    Write_RMW_virtual_word(diff_16);
    }

#if !(defined(__i386__) && defined(__GNUC__) && BX_SupportHostAsms)
  SET_FLAGS_OSZAPC_16(op1_16, op2_16, diff_16, BX_INSTR_SUB16);
#endif
}

  void
BX_CPU_C::CMP_EwIw(bxInstruction_c *i)
{
  Bit16u op2_16, op1_16;

  op2_16 = i->Iw();

  if (i->modC0()) {
    op1_16 = BX_READ_16BIT_REG(i->rm());
    }
  else {
    read_virtual_word(i->seg(), RMAddr(i), &op1_16);
    }

#if (defined(__i386__) && defined(__GNUC__) && BX_SupportHostAsms)
  Bit32u flags32;

  asmCmp16(op1_16, op2_16, flags32);
  setEFlagsOSZAPC(flags32);
#else
  Bit16u diff_16;
  diff_16 = op1_16 - op2_16;

  SET_FLAGS_OSZAPC_16(op1_16, op2_16, diff_16, BX_INSTR_CMP16);
#endif
}



  void
BX_CPU_C::NEG_Ew(bxInstruction_c *i)
{
  Bit16u op1_16, diff_16;


  if (i->modC0()) {
    op1_16 = BX_READ_16BIT_REG(i->rm());
    diff_16 = 0 - op1_16;
    BX_WRITE_16BIT_REG(i->rm(), diff_16);
    }
  else {
    read_RMW_virtual_word(i->seg(), RMAddr(i), &op1_16);
    diff_16 = 0 - op1_16;
    Write_RMW_virtual_word(diff_16);
    }

  SET_FLAGS_OSZAPC_16(op1_16, 0, diff_16, BX_INSTR_NEG16);
}


  void
BX_CPU_C::INC_Ew(bxInstruction_c *i)
{
  Bit16u op1_16;

  if (i->modC0()) {
    op1_16 = BX_READ_16BIT_REG(i->rm());
    op1_16++;
    BX_WRITE_16BIT_REG(i->rm(), op1_16);
    }
  else {
    read_RMW_virtual_word(i->seg(), RMAddr(i), &op1_16);
    op1_16++;
    Write_RMW_virtual_word(op1_16);
    }

  SET_FLAGS_OSZAP_16(0, 0, op1_16, BX_INSTR_INC16);
}


  void
BX_CPU_C::DEC_Ew(bxInstruction_c *i)
{
  Bit16u op1_16;

  if (i->modC0()) {
#if (defined(__i386__) && defined(__GNUC__) && BX_SupportHostAsms)
    Bit32u flags32;

    asmDec16(BX_CPU_THIS_PTR gen_reg[i->rm()].word.rx, flags32);
    setEFlagsOSZAP(flags32);
#else
    op1_16 = BX_READ_16BIT_REG(i->rm());
    op1_16--;
    BX_WRITE_16BIT_REG(i->rm(), op1_16);
#endif
    }
  else {
    read_RMW_virtual_word(i->seg(), RMAddr(i), &op1_16);
#if (defined(__i386__) && defined(__GNUC__) && BX_SupportHostAsms)
    Bit32u flags32;

    asmDec16(op1_16, flags32);
    setEFlagsOSZAP(flags32);
#else
    op1_16--;
#endif
    Write_RMW_virtual_word(op1_16);
    }

#if !(defined(__i386__) && defined(__GNUC__) && BX_SupportHostAsms)
  SET_FLAGS_OSZAP_16(0, 0, op1_16, BX_INSTR_DEC16);
#endif
}


  void
BX_CPU_C::CMPXCHG_EwGw(bxInstruction_c *i)
{
#if (BX_CPU_LEVEL >= 4) || (BX_CPU_LEVEL_HACKED >= 4)

  Bit16u op2_16, op1_16, diff_16;

  if (i->modC0()) {
    op1_16 = BX_READ_16BIT_REG(i->rm());
    }
  else {
    read_RMW_virtual_word(i->seg(), RMAddr(i), &op1_16);
    }

  diff_16 = AX - op1_16;

  SET_FLAGS_OSZAPC_16(AX, op1_16, diff_16, BX_INSTR_CMP16);

  if (diff_16 == 0) {  // if accumulator == dest
    // ZF = 1
    set_ZF(1);
    // dest <-- src
    op2_16 = BX_READ_16BIT_REG(i->nnn());

    if (i->modC0()) {
      BX_WRITE_16BIT_REG(i->rm(), op2_16);
      }
    else {
      Write_RMW_virtual_word(op2_16);
      }
    }
  else {
    // ZF = 0
    set_ZF(0);
    // accumulator <-- dest
    AX = op1_16;
    }

#else
  BX_PANIC(("CMPXCHG_EwGw:"));
#endif
}