$finish() now stops at the end of the time step not immediately.

[iverilog.git] / expr_synth.cc

/*
 * Copyright (c) 1999-2005 Stephen Williams (steve@icarus.com)
 *
 *    This source code is free software; you can redistribute it
 *    and/or modify it in source code form 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
 */
#ifdef HAVE_CVS_IDENT
#ident "$Id: expr_synth.cc,v 1.87 2007/06/02 03:42:12 steve Exp $"
#endif

# include "config.h"

# include  <iostream>

# include  "netlist.h"
# include  "netmisc.h"
# include  "ivl_assert.h"

NetNet* NetExpr::synthesize(Design*des)
{
      cerr << get_line() << ": internal error: cannot synthesize expression: "
           << *this << endl;
      des->errors += 1;
      return 0;
}

/*
 * Make an LPM_ADD_SUB device from addition operators.
 */
NetNet* NetEBAdd::synthesize(Design*des)
{
      assert((op()=='+') || (op()=='-'));

      NetNet*lsig = left_->synthesize(des);
      NetNet*rsig = right_->synthesize(des);

      assert(expr_width() >= lsig->vector_width());
      assert(expr_width() >= rsig->vector_width());

      lsig = pad_to_width(des, lsig, expr_width());
      rsig = pad_to_width(des, rsig, expr_width());

      assert(lsig->vector_width() == rsig->vector_width());
      unsigned width=lsig->vector_width();

      perm_string path = lsig->scope()->local_symbol();
      NetNet*osig = new NetNet(lsig->scope(), path, NetNet::IMPLICIT, width);
      osig->local_flag(true);
      osig->data_type(expr_type());

      perm_string oname = osig->scope()->local_symbol();
      NetAddSub *adder = new NetAddSub(lsig->scope(), oname, width);
      connect(lsig->pin(0), adder->pin_DataA());
      connect(rsig->pin(0), adder->pin_DataB());
      connect(osig->pin(0), adder->pin_Result());
      des->add_node(adder);

      switch (op()) {
          case '+':
            adder->attribute(perm_string::literal("LPM_Direction"), verinum("ADD"));
            break;
          case '-':
            adder->attribute(perm_string::literal("LPM_Direction"), verinum("SUB"));
            break;
      }

      return osig;
}

/*
 * The bitwise logic operators are turned into discrete gates pretty
 * easily. Synthesize the left and right sub-expressions to get
 * signals, then just connect a single gate to each bit of the vector
 * of the expression.
 */
NetNet* NetEBBits::synthesize(Design*des)
{
      NetNet*lsig = left_->synthesize(des);
      NetNet*rsig = right_->synthesize(des);

      NetScope*scope = lsig->scope();
      assert(scope);

      if (lsig->vector_width() != rsig->vector_width()) {
            cerr << get_line() << ": internal error: bitwise (" << op_
                 << ") widths do not match: " << lsig->vector_width()
                 << " != " << rsig->vector_width() << endl;
            cerr << get_line() << ":               : width="
                 << lsig->vector_width() << ": " << *left_ << endl;
            cerr << get_line() << ":               : width="
                 << rsig->vector_width() << ": " << *right_ << endl;
            return 0;
      }

      assert(lsig->vector_width() == rsig->vector_width());
      NetNet*osig = new NetNet(scope, scope->local_symbol(),
                               NetNet::IMPLICIT, lsig->vector_width());
      osig->local_flag(true);
      osig->data_type(expr_type());

      perm_string oname = scope->local_symbol();
      unsigned wid = lsig->vector_width();
      NetLogic*gate;

      switch (op()) {
          case '&':
            gate = new NetLogic(scope, oname, 3, NetLogic::AND, wid);
            break;
          case '|':
            gate = new NetLogic(scope, oname, 3, NetLogic::OR, wid);
            break;
          case '^':
            gate = new NetLogic(scope, oname, 3, NetLogic::XOR, wid);
            break;
          case 'O':
            gate = new NetLogic(scope, oname, 3, NetLogic::NOR, wid);
            break;
          case 'X':
            gate = new NetLogic(scope, oname, 3, NetLogic::XNOR, wid);
            break;
          default:
            assert(0);
      }

      connect(osig->pin(0), gate->pin(0));
      connect(lsig->pin(0), gate->pin(1));
      connect(rsig->pin(0), gate->pin(2));

      gate->set_line(*this);
      des->add_node(gate);

      return osig;
}

NetNet* NetEBComp::synthesize(Design*des)
{

      NetNet*lsig = left_->synthesize(des);
      NetNet*rsig = right_->synthesize(des);

      NetScope*scope = lsig->scope();
      assert(scope);

      unsigned width = lsig->vector_width();
      if (rsig->vector_width() > width)
            width = rsig->vector_width();

      lsig = pad_to_width(des, lsig, width);
      rsig = pad_to_width(des, rsig, width);

      NetNet*osig = new NetNet(scope, scope->local_symbol(),
                               NetNet::IMPLICIT, 1);
      osig->set_line(*this);
      osig->local_flag(true);
      osig->data_type(IVL_VT_LOGIC);

        /* Handle the special case of a single bit equality
           operation. Make an XNOR gate instead of a comparator. */
      if ((width == 1) && ((op_ == 'e') || (op_ == 'E'))) {
            NetLogic*gate = new NetLogic(scope, scope->local_symbol(),
                                         3, NetLogic::XNOR, 1);
            gate->set_line(*this);
            connect(gate->pin(0), osig->pin(0));
            connect(gate->pin(1), lsig->pin(0));
            connect(gate->pin(2), rsig->pin(0));
            des->add_node(gate);
            return osig;
      }

        /* Handle the special case of a single bit inequality
           operation. This is similar to single bit equality, but uses
           an XOR instead of an XNOR gate. */
      if ((width == 1) && ((op_ == 'n') || (op_ == 'N'))) {
            NetLogic*gate = new NetLogic(scope, scope->local_symbol(),
                                         3, NetLogic::XOR, 1);
            gate->set_line(*this);
            connect(gate->pin(0), osig->pin(0));
            connect(gate->pin(1), lsig->pin(0));
            connect(gate->pin(2), rsig->pin(0));
            des->add_node(gate);
            return osig;
      }


      NetCompare*dev = new NetCompare(scope, scope->local_symbol(), width);
      dev->set_line(*this);
      des->add_node(dev);

      connect(dev->pin_DataA(), lsig->pin(0));
      connect(dev->pin_DataB(), rsig->pin(0));


      switch (op_) {
          case '<':
            connect(dev->pin_ALB(), osig->pin(0));
            break;
          case '>':
            connect(dev->pin_AGB(), osig->pin(0));
            break;
          case 'e': // ==
          case 'E': // === ?
            connect(dev->pin_AEB(), osig->pin(0));
            break;
          case 'G': // >=
            connect(dev->pin_AGEB(), osig->pin(0));
            break;
          case 'L': // <=
            connect(dev->pin_ALEB(), osig->pin(0));
            break;
          case 'n': // !=
          case 'N': // !==
            connect(dev->pin_ANEB(), osig->pin(0));
            break;

          default:
            cerr << get_line() << ": internal error: cannot synthesize "
                  "comparison: " << *this << endl;
            des->errors += 1;
            return 0;
      }

      return osig;
}

NetNet* NetEBPow::synthesize(Design*des)
{
      cerr << get_line() << ": internal error: Do not yet know how to handle"
           << " power operator in this context." << endl;
      des->errors += 1;
      return 0;
}

NetNet* NetEBMult::synthesize(Design*des)
{
      NetNet*lsig = left_->synthesize(des);
      NetNet*rsig = right_->synthesize(des);

      if (lsig == 0)
            return 0;

      if (rsig == 0)
            return 0;

      NetScope*scope = lsig->scope();
      assert(scope);

      NetMult*mult = new NetMult(scope, scope->local_symbol(),
                                 expr_width(),
                                 lsig->vector_width(),
                                 rsig->vector_width());
      des->add_node(mult);

      mult->set_signed( has_sign() );
      mult->set_line(*this);

      connect(mult->pin_DataA(), lsig->pin(0));
      connect(mult->pin_DataB(), rsig->pin(0));

      NetNet*osig = new NetNet(scope, scope->local_symbol(),
                               NetNet::IMPLICIT, expr_width());
      osig->data_type(lsig->data_type());
      osig->set_line(*this);
      osig->data_type(expr_type());
      osig->local_flag(true);

      connect(mult->pin_Result(), osig->pin(0));

      return osig;
}

NetNet* NetEBDiv::synthesize(Design*des)
{
      NetNet*lsig = left_->synthesize(des);
      NetNet*rsig  = right_->synthesize(des);

      NetScope*scope = lsig->scope();

      NetNet*osig = new NetNet(scope, scope->local_symbol(),
                               NetNet::IMPLICIT, expr_width());
      osig->set_line(*this);
      osig->data_type(lsig->data_type());
      osig->local_flag(true);

      switch (op()) {

          case '/': {
                NetDivide*div = new NetDivide(scope, scope->local_symbol(),
                                              expr_width(),
                                              lsig->vector_width(),
                                              rsig->vector_width());
                div->set_line(*this);
                des->add_node(div);

                connect(div->pin_DataA(), lsig->pin(0));
                connect(div->pin_DataB(), rsig->pin(0));
                connect(div->pin_Result(),osig->pin(0));
                break;
          }

          case '%': {
                NetModulo*div = new NetModulo(scope, scope->local_symbol(),
                                              expr_width(),
                                              lsig->vector_width(),
                                              rsig->vector_width());
                div->set_line(*this);
                des->add_node(div);

                connect(div->pin_DataA(), lsig->pin(0));
                connect(div->pin_DataB(), rsig->pin(0));
                connect(div->pin_Result(),osig->pin(0));
                break;
          }

          default: {
                cerr << get_line() << ": internal error: "
                     << "NetEBDiv has unexpeced op() code: "
                     << op() << endl;
                des->errors += 1;

                delete osig;
                return 0;
          }
      }

      return osig;
}

NetNet* NetEBLogic::synthesize(Design*des)
{
      NetNet*lsig = left_->synthesize(des);
      NetNet*rsig = right_->synthesize(des);

      if (lsig == 0)
            return 0;

      if (rsig == 0)
            return 0;

      NetScope*scope = lsig->scope();
      assert(scope);

      NetNet*osig = new NetNet(scope, scope->local_symbol(),
                               NetNet::IMPLICIT, 1);
      osig->data_type(expr_type());
      osig->local_flag(true);


      if (op() == 'o') {

              /* Logic OR can handle the reduction *and* the logical
                 comparison with a single wide OR gate. So handle this
                 magically. */

            perm_string oname = scope->local_symbol();

            NetLogic*olog = new NetLogic(scope, oname,
                                         lsig->pin_count()+rsig->pin_count()+1,
                                         NetLogic::OR, 1);

            connect(osig->pin(0), olog->pin(0));

            unsigned pin = 1;
            for (unsigned idx = 0 ;  idx < lsig->pin_count() ;  idx = 1)
                  connect(olog->pin(pin+idx), lsig->pin(idx));

            pin += lsig->pin_count();
            for (unsigned idx = 0 ;  idx < rsig->pin_count() ;  idx = 1)
                  connect(olog->pin(pin+idx), rsig->pin(idx));

            des->add_node(olog);

      } else {
            assert(op() == 'a');

              /* Create the logic AND gate. This is a single bit
                 output, with inputs for each of the operands. */
            NetLogic*olog;
            perm_string oname = scope->local_symbol();

            olog = new NetLogic(scope, oname, 3, NetLogic::AND, 1);

            connect(osig->pin(0), olog->pin(0));
            des->add_node(olog);

              /* XXXX Here, I need to reduce the parameters with
                 reduction or. */


              /* By this point, the left and right parameters have been
                 reduced to single bit values. Now we just connect them to
                 the logic gate. */
            assert(lsig->pin_count() == 1);
            connect(lsig->pin(0), olog->pin(1));

            assert(rsig->pin_count() == 1);
            connect(rsig->pin(0), olog->pin(2));
      }


      return osig;
}

NetNet* NetEBShift::synthesize(Design*des)
{
      if (! dynamic_cast<NetEConst*>(right_)) {
            NetExpr*tmp = right_->eval_tree();
            if (tmp) {
                  delete right_;
                  right_ = tmp;
            }
      }

      NetNet*lsig = left_->synthesize(des);
      if (lsig == 0)
            return 0;

      bool right_flag  =  op_ == 'r' || op_ == 'R';
      bool signed_flag =  op_ == 'R';

      NetScope*scope = lsig->scope();

        /* Detect the special case where the shift amount is
           constant. Evaluate the shift amount, and simply reconnect
           the left operand to the output, but shifted. */
      if (NetEConst*rcon = dynamic_cast<NetEConst*>(right_)) {
            verinum shift_v = rcon->value();
            long shift = shift_v.as_long();

            if (op() == 'r')
                  shift = 0-shift;

            if (shift == 0)
                  return lsig;

            NetNet*osig = new NetNet(scope, scope->local_symbol(),
                                     NetNet::IMPLICIT, expr_width());
            osig->data_type(expr_type());
            osig->local_flag(true);

              // ushift is the amount of pad created by the shift.
            unsigned long ushift = shift>=0? shift : -shift;
            if (ushift > osig->vector_width())
                  ushift = osig->vector_width();

              // part_width is the bits of the vector that survive the shift.
            unsigned long part_width = osig->vector_width() - ushift;

            verinum znum (verinum::V0, ushift, true);
            NetConst*zcon = new NetConst(scope, scope->local_symbol(),
                                         znum);
            des->add_node(zcon);

              /* Detect the special case that the shift is the size of
                 the whole expression. Simply connect the pad to the
                 osig and escape. */
            if (ushift >= osig->vector_width()) {
                  connect(zcon->pin(0), osig->pin(0));
                  return osig;
            }

            NetNet*zsig = new NetNet(scope, scope->local_symbol(),
                                     NetNet::WIRE, znum.len());
            zsig->data_type(osig->data_type());
            zsig->local_flag(true);
            zsig->set_line(*this);
            connect(zcon->pin(0), zsig->pin(0));

              /* Create a part select to reduce the width of the lsig
                 to the amount left by the shift. */
            NetPartSelect*psel = new NetPartSelect(lsig, shift<0? ushift : 0,
                                                   part_width,
                                                   NetPartSelect::VP);
            des->add_node(psel);

            NetNet*psig = new NetNet(scope, scope->local_symbol(),
                                     NetNet::IMPLICIT, part_width);
            psig->data_type(expr_type());
            psig->local_flag(true);
            psig->set_line(*this);
            connect(psig->pin(0), psel->pin(0));

            NetConcat*ccat = new NetConcat(scope, scope->local_symbol(),
                                           osig->vector_width(), 2);
            ccat->set_line(*this);
            des->add_node(ccat);

            connect(ccat->pin(0), osig->pin(0));
            if (shift > 0) {
                    // Left shift.
                  connect(ccat->pin(1), zsig->pin(0));
                  connect(ccat->pin(2), psig->pin(0));
            } else {
                    // Right shift
                  connect(ccat->pin(1), psig->pin(0));
                  connect(ccat->pin(2), zsig->pin(0));
            }

            return osig;
      }

      NetNet*rsig = right_->synthesize(des);
      if (rsig == 0)
            return 0;

      NetNet*osig = new NetNet(scope, scope->local_symbol(),
                               NetNet::IMPLICIT, expr_width());
      osig->data_type(expr_type());
      osig->local_flag(true);

      NetCLShift*dev = new NetCLShift(scope, scope->local_symbol(),
                                      osig->vector_width(),
                                      rsig->vector_width(),
                                      right_flag, signed_flag);
      dev->set_line(*this);
      des->add_node(dev);

      connect(dev->pin_Result(), osig->pin(0));

      assert(lsig->vector_width() == dev->width());
      connect(dev->pin_Data(), lsig->pin(0));

      connect(dev->pin_Distance(), rsig->pin(0));

      return osig;
}

NetNet* NetEConcat::synthesize(Design*des)
{
        /* First, synthesize the operands. */
      NetNet**tmp = new NetNet*[parms_.count()];
      bool flag = true;
      for (unsigned idx = 0 ;  idx < parms_.count() ;  idx += 1) {
            tmp[idx] = parms_[idx]->synthesize(des);
            if (tmp[idx] == 0)
                  flag = false;
      }

      if (flag == false)
            return 0;

      assert(tmp[0]);
      NetScope*scope = tmp[0]->scope();
      assert(scope);

        /* Make a NetNet object to carry the output vector. */
      perm_string path = scope->local_symbol();
      NetNet*osig = new NetNet(scope, path, NetNet::IMPLICIT, expr_width());
      osig->local_flag(true);
      osig->data_type(tmp[0]->data_type());

      NetConcat*concat = new NetConcat(scope, scope->local_symbol(),
                                       osig->vector_width(), parms_.count());
      concat->set_line(*this);
      des->add_node(concat);
      connect(concat->pin(0), osig->pin(0));

      for (unsigned idx = 0 ;  idx < parms_.count() ;  idx += 1) {
            connect(concat->pin(idx+1), tmp[parms_.count()-idx-1]->pin(0));
      }

      delete[]tmp;
      return osig;
}

NetNet* NetEConst::synthesize(Design*des)
{
      NetScope*scope = des->find_root_scope();
      assert(scope);

      perm_string path = scope->local_symbol();
      unsigned width=expr_width();

      NetNet*osig = new NetNet(scope, path, NetNet::IMPLICIT, width-1,0);
      osig->local_flag(true);
      osig->data_type(IVL_VT_LOGIC);
      osig->set_signed(has_sign());
      NetConst*con = new NetConst(scope, scope->local_symbol(), value());
      connect(osig->pin(0), con->pin(0));

      des->add_node(con);
      return osig;
}

/*
* Create a NetLiteral object to represent real valued constants.
*/
NetNet* NetECReal::synthesize(Design*des)
{
      NetScope*scope = des->find_root_scope();
      assert(scope);

      perm_string path = scope->local_symbol();

      NetNet*osig = new NetNet(scope, path, NetNet::WIRE, 1);
      osig->local_flag(true);
      osig->data_type(IVL_VT_REAL);
      osig->set_signed(has_sign());
      osig->set_line(*this);

      NetLiteral*con = new NetLiteral(scope, scope->local_symbol(), value_);
      des->add_node(con);
      con->set_line(*this);

      connect(osig->pin(0), con->pin(0));
      return osig;
}

/*
 * The bitwise unary logic operator (there is only one) is turned
 * into discrete gates just as easily as the binary ones above.
 */
NetNet* NetEUBits::synthesize(Design*des)
{
      NetNet*isig = expr_->synthesize(des);

      NetScope*scope = isig->scope();
      assert(scope);

      unsigned width = isig->vector_width();
      NetNet*osig = new NetNet(scope, scope->local_symbol(),
                               NetNet::IMPLICIT, width);
      osig->data_type(expr_type());
      osig->local_flag(true);

      perm_string oname = scope->local_symbol();
      NetLogic*gate;

      switch (op()) {
          case '~':
            gate = new NetLogic(scope, oname, 2, NetLogic::NOT, width);
            break;
          default:
            assert(0);
      }

      connect(osig->pin(0), gate->pin(0));
      connect(isig->pin(0), gate->pin(1));

      des->add_node(gate);

      return osig;
}

NetNet* NetEUReduce::synthesize(Design*des)
{
      NetNet*isig = expr_->synthesize(des);

      NetScope*scope = isig->scope();
      assert(scope);

      NetNet*osig = new NetNet(scope, scope->local_symbol(),
                               NetNet::IMPLICIT, 1);
      osig->data_type(expr_type());
      osig->local_flag(true);

      NetUReduce::TYPE rtype = NetUReduce::NONE;

      switch (op()) {
          case 'N':
          case '!':
            rtype = NetUReduce::NOR;
            break;
          case '&':
            rtype = NetUReduce::AND;
            break;
          case '|':
            rtype = NetUReduce::OR;
            break;
          case '^':
            rtype = NetUReduce::XOR;
            break;
          case 'A':
            rtype = NetUReduce::XNOR;
            break;
          case 'X':
            rtype = NetUReduce::XNOR;
            break;
          default:
            cerr << get_line() << ": internal error: "
                 << "Unable to synthesize " << *this << "." << endl;
            return 0;
      }

      NetUReduce*gate = new NetUReduce(scope, scope->local_symbol(),
                                       rtype, isig->vector_width());

      des->add_node(gate);
      connect(gate->pin(0), osig->pin(0));
      for (unsigned idx = 0 ;  idx < isig->pin_count() ;  idx += 1)
            connect(gate->pin(1+idx), isig->pin(idx));

      return osig;
}

NetNet* NetESelect::synthesize(Design *des)
{

      NetNet*sub = expr_->synthesize(des);
      if (sub == 0)
            return 0;

      NetScope*scope = sub->scope();

      NetNet*off = 0;

        // This handles the case that the NetESelect exists to do an
        // actual part/bit select. Generate a NetPartSelect object to
        // do the work, and replace "sub" with the selected output.
      if (base_ != 0) {
            off = base_->synthesize(des);

            NetPartSelect*sel = new NetPartSelect(sub, off, expr_width());
            sel->set_line(*this);
            des->add_node(sel);

            NetNet*tmp = new NetNet(scope, scope->local_symbol(),
                                    NetNet::IMPLICIT, expr_width());
            tmp->data_type(sub->data_type());
            tmp->local_flag(true);
            tmp->set_line(*this);
            sub = tmp;
            connect(sub->pin(0), sel->pin(0));
      }


        // Now look for the case that the NetESelect actually exists
        // to change the width of the expression. (i.e. to do
        // padding.) If this was for an actual part select that at
        // this point the output vector_width is exactly right, and we
        // are done.
      if (sub->vector_width() == expr_width())
            return sub;

        // The vector_width is not exactly right, so the source is
        // probably asking for padding. Create nodes to do sign
        // extension or 0 extension, depending on the has_sign() mode
        // of the expression.

      NetNet*net = new NetNet(scope, scope->local_symbol(),
                              NetNet::IMPLICIT, expr_width());
      net->data_type(expr_type());
      net->local_flag(true);
      net->set_line(*this);
      if (has_sign()) {
            NetSignExtend*pad = new NetSignExtend(scope,
                                                  scope->local_symbol(),
                                                  expr_width());
            pad->set_line(*this);
            des->add_node(pad);

            connect(pad->pin(1), sub->pin(0));
            connect(pad->pin(0), net->pin(0));

      } else {

            NetConcat*cat = new NetConcat(scope, scope->local_symbol(),
                                          expr_width(), 2);
            cat->set_line(*this);
            des->add_node(cat);

            assert(expr_width() > sub->vector_width());
            unsigned pad_width = expr_width() - sub->vector_width();
            verinum pad((uint64_t)0, pad_width);
            NetConst*con = new NetConst(scope, scope->local_symbol(),
                                        pad);
            con->set_line(*this);
            des->add_node(con);

            NetNet*tmp = new NetNet(scope, scope->local_symbol(),
                                    NetNet::IMPLICIT, pad_width);
            tmp->data_type(expr_type());
            tmp->local_flag(true);
            tmp->set_line(*this);
            connect(tmp->pin(0), con->pin(0));

            connect(cat->pin(0), net->pin(0));
            connect(cat->pin(1), sub->pin(0));
            connect(cat->pin(2), con->pin(0));
      }

      return net;
}

/*
 * Synthesize a ?: operator as a NetMux device. Connect the condition
 * expression to the select input, then connect the true and false
 * expressions to the B and A inputs. This way, when the select input
 * is one, the B input, which is the true expression, is selected.
 */
NetNet* NetETernary::synthesize(Design *des)
{
      NetNet*csig = cond_->synthesize(des);
      NetNet*tsig = true_val_->synthesize(des);
      NetNet*fsig = false_val_->synthesize(des);

      perm_string path = csig->scope()->local_symbol();

      assert(csig->vector_width() == 1);

      unsigned width=expr_width();
      NetNet*osig = new NetNet(csig->scope(), path, NetNet::IMPLICIT, width);
      osig->data_type(expr_type());
      osig->local_flag(true);

        /* Make sure both value operands are the right width. */
      tsig = crop_to_width(des, pad_to_width(des, tsig, width), width);
      fsig = crop_to_width(des, pad_to_width(des, fsig, width), width);

      assert(width == tsig->vector_width());
      assert(width == fsig->vector_width());

      perm_string oname = csig->scope()->local_symbol();
      NetMux *mux = new NetMux(csig->scope(), oname, width,
                               2, csig->vector_width());
      connect(tsig->pin(0), mux->pin_Data(1));
      connect(fsig->pin(0), mux->pin_Data(0));
      connect(osig->pin(0), mux->pin_Result());
      connect(csig->pin(0), mux->pin_Sel());
      des->add_node(mux);

      return osig;
}

/*
 * When synthesizing a signal expression, it is usually fine to simply
 * return the NetNet that it refers to. If this is a part select,
 * though, a bit more work needs to be done. Return a temporary that
 * represents the connections to the selected bits.
 *
 * For example, if there is a reg foo, like so:
 *     reg [5:0] foo;
 * and this expression node represents a part select foo[3:2], then
 * create a temporary like so:
 *
 *                     foo
 *                    +---+
 *                    | 5 |
 *                    +---+
 *         tmp        | 4 |
 *        +---+       +---+
 *        | 1 | <---> | 3 |
 *        +---+       +---+
 *        | 0 | <---> | 2 |
 *        +---+       +---+
 *                    | 1 |
 *                    +---+
 *                    | 0 |
 *                    +---+
 * The temporary is marked as a temporary and returned to the
 * caller. This causes the caller to get only the selected part of the
 * signal, and when it hooks up to tmp, it hooks up to the right parts
 * of foo.
 */
NetNet* NetESignal::synthesize(Design*des)
{
      return net_;
}

/*
 * $Log: expr_synth.cc,v $
 * Revision 1.87  2007/06/02 03:42:12  steve
 *  Properly evaluate scope path expressions.
 *
 * Revision 1.86  2007/04/15 01:37:29  steve
 *  Allow bit/part select of vectors in continuous assignments.
 *
 * Revision 1.85  2007/04/12 05:21:54  steve
 *  fix handling of unary reduction logic in certain nets.
 *
 * Revision 1.84  2007/04/04 02:31:57  steve
 *  Remove useless assert
 *
 * Revision 1.83  2007/02/05 01:42:31  steve
 *  Set some missing local flags.
 *
 * Revision 1.82  2007/01/20 02:10:45  steve
 *  Get argument widths right for shift results.
 *
 * Revision 1.81  2007/01/16 05:44:15  steve
 *  Major rework of array handling. Memories are replaced with the
 *  more general concept of arrays. The NetMemory and NetEMemory
 *  classes are removed from the ivl core program, and the IVL_LPM_RAM
 *  lpm type is removed from the ivl_target API.
 *
 * Revision 1.80  2006/08/08 05:11:37  steve
 *  Handle 64bit delay constants.
 *
 * Revision 1.79  2006/07/31 03:50:17  steve
 *  Add support for power in constant expressions.
 *
 * Revision 1.78  2006/07/08 21:48:46  steve
 *  Handle real valued literals in net contexts.
 *
 * Revision 1.77  2006/05/01 20:47:59  steve
 *  More explicit datatype setup.
 *
 * Revision 1.76  2006/05/01 05:40:21  steve
 *  fix net type of multiply output.
 *
 * Revision 1.75  2006/04/30 05:17:48  steve
 *  Get the data type of part select results right.
 *
 * Revision 1.74  2006/01/03 05:15:33  steve
 *  Fix the return type of a synthesized divide.
 *
 * Revision 1.73  2005/09/15 23:04:09  steve
 *  Make sure div, mod and mult nodes have line number info.
 *
 * Revision 1.72  2005/08/31 05:07:31  steve
 *  Handle memory references is continuous assignments.
 *
 * Revision 1.71  2005/06/13 23:22:14  steve
 *  use NetPartSelect to shrink part from high bits.
 *
 * Revision 1.70  2005/06/13 22:26:03  steve
 *  Make synthesized padding vector-aware.
 *
 * Revision 1.69  2005/05/15 04:47:00  steve
 *  synthesis of Logic and shifts using vector gates.
 *
 * Revision 1.68  2005/05/06 00:25:13  steve
 *  Handle synthesis of concatenation expressions.
 *
 * Revision 1.67  2005/04/25 01:30:31  steve
 *  synthesis of add and unary get vector widths right.
 *
 * Revision 1.66  2005/04/24 23:44:02  steve
 *  Update DFF support to new data flow.
 *
 * Revision 1.65  2005/03/12 06:43:35  steve
 *  Update support for LPM_MOD.
 *
 * Revision 1.64  2005/02/19 02:43:38  steve
 *  Support shifts and divide.
 *
 * Revision 1.63  2005/02/12 06:25:40  steve
 *  Restructure NetMux devices to pass vectors.
 *  Generate NetMux devices from ternary expressions,
 *  Reduce NetMux devices to bufif when appropriate.
 *
 * Revision 1.62  2005/01/28 05:39:33  steve
 *  Simplified NetMult and IVL_LPM_MULT.
 *
 * Revision 1.61  2005/01/16 04:20:32  steve
 *  Implement LPM_COMPARE nodes as two-input vector functors.
 *
 * Revision 1.60  2004/12/11 02:31:26  steve
 *  Rework of internals to carry vectors through nexus instead
 *  of single bits. Make the ivl, tgt-vvp and vvp initial changes
 *  down this path.
 *
 * Revision 1.59  2004/06/30 02:16:26  steve
 *  Implement signed divide and signed right shift in nets.
 *
 * Revision 1.58  2004/06/16 16:21:34  steve
 *  Connect rsif of multiply to DataB.
 *
 * Revision 1.57  2004/06/12 15:00:02  steve
 *  Support / and % in synthesized contexts.
 *
 * Revision 1.56  2004/06/01 01:04:57  steve
 *  Fix synthesis method for logical and/or
 *
 * Revision 1.55  2004/02/20 18:53:35  steve
 *  Addtrbute keys are perm_strings.
 *
 * Revision 1.54  2004/02/18 17:11:56  steve
 *  Use perm_strings for named langiage items.
 *
 * Revision 1.53  2004/02/15 04:23:48  steve
 *  Fix evaluation of compare to constant expression.
 *
 * Revision 1.52  2003/11/10 19:39:20  steve
 *  Remove redundant scope tokens.
 *
 * Revision 1.51  2003/10/27 06:04:21  steve
 *  More flexible width handling for synthesized add.
 *
 * Revision 1.50  2003/09/26 02:44:27  steve
 *  Assure ternary arguments are wide enough.
 *
 * Revision 1.49  2003/09/03 23:31:36  steve
 *  Support synthesis of constant downshifts.
 *
 * Revision 1.48  2003/08/28 04:11:18  steve
 *  Spelling patch.
 *
 * Revision 1.47  2003/08/09 03:23:40  steve
 *  Add support for IVL_LPM_MULT device.
 *
 * Revision 1.46  2003/07/26 03:34:42  steve
 *  Start handling pad of expressions in code generators.
 *
 * Revision 1.45  2003/06/24 01:38:02  steve
 *  Various warnings fixed.
 *
 * Revision 1.44  2003/04/19 04:52:56  steve
 *  Less picky about expression widths while synthesizing ternary.
 *
 * Revision 1.43  2003/04/08 05:07:15  steve
 *  Detect constant shift distances in synthesis.
 *
 * Revision 1.42  2003/04/08 04:33:55  steve
 *  Synthesize shift expressions.
 *
 * Revision 1.41  2003/03/06 00:28:41  steve
 *  All NetObj objects have lex_string base names.
 *
 * Revision 1.40  2003/02/26 01:29:24  steve
 *  LPM objects store only their base names.
 *
 * Revision 1.39  2003/01/30 16:23:07  steve
 *  Spelling fixes.
 *
 * Revision 1.38  2003/01/26 21:15:58  steve
 *  Rework expression parsing and elaboration to
 *  accommodate real/realtime values and expressions.
 *
 * Revision 1.37  2002/11/17 23:37:55  steve
 *  Magnitude compare to 0.
 *
 * Revision 1.36  2002/08/12 01:34:59  steve
 *  conditional ident string using autoconfig.
 *
 * Revision 1.35  2002/07/07 22:31:39  steve
 *  Smart synthesis of binary AND expressions.
 *
 * Revision 1.34  2002/07/05 21:26:17  steve
 *  Avoid emitting to vvp local net symbols.
 *
 * Revision 1.33  2002/05/26 01:39:02  steve
 *  Carry Verilog 2001 attributes with processes,
 *  all the way through to the ivl_target API.
 *
 *  Divide signal reference counts between rval
 *  and lval references.
 */