set_width.cc

/*
 * Copyright (c) 1999-2008 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
 */

# include "config.h"

# include  <iostream>

/*
 * This file contains set_width methods for the various NetExpr
 * classes. The set_width method is used by elaboration to ask the
 * expression to resize itself. If the expression can't, then the
 * set_width method will return false and the caller will arrange for
 * whatever is needed to deal with the size mismatch.
 */
# include  "netlist.h"
# include  "netmisc.h"
# include  "compiler.h"
# include  <typeinfo>


bool NetExpr::set_width(unsigned w, bool)
{
      cerr << get_fileline() << ": internal warning:  "
	   <<typeid(*this).name() << ": set_width(unsigned) "
	   << "not implemented." << endl;
      expr_width(w);
      return false;
}

bool NetEBinary::set_width(unsigned w, bool)
{
      bool flag = true;
      switch (op_) {

	  case 'l': // left shift  (<<)
	  case 'r': // right shift (>>)
	      /* these operators are handled in the derived class. */
	    assert(0);
	    break;

	      /* The default rule is that the operands of the binary
		 operator might as well use the same width as the
		 output from the binary operation. */
	  default:
	    expr_width(left_->expr_width() > right_->expr_width()
			  ? left_->expr_width() : right_->expr_width());
	    cerr << "NetEBinary::set_width(): Using default for " <<
		  op_ << "." << endl;
	    flag = false;

	  case '%':
	  case '/':
	    flag = left_->set_width(w) && flag;
	    flag = right_->set_width(w) && flag;
	    expr_width(w);
	    break;
      }
      return flag;
}

/*
 * The bitwise logical operators have operands the same size as the
 * result. Anything else is a mess.
 */
bool NetEBAdd::set_width(unsigned w, bool)
{

      unsigned wid = w;
      if (left_->expr_width() > wid)
	    wid = left_->expr_width();
      if (right_->expr_width() > wid)
	    wid = right_->expr_width();

      left_->set_width(wid);
      right_->set_width(wid);

      if (left_->expr_width() < wid) {
	    NetExpr*tmp = new NetESelect(left_, 0, wid);
	    tmp->cast_signed(left_->has_sign());
	    left_ = tmp;
      }

      if (right_->expr_width() < wid) {
	    NetExpr*tmp = new NetESelect(right_, 0, wid);
	    tmp->cast_signed(right_->has_sign());
	    right_ = tmp;
      }

      expr_width(wid);
      return wid == w;
}

/*
 * The bitwise logical operators have operands the same size as the
 * result. Anything else is a mess. I first try to get the operands to
 * shrink to the desired size. I then expand operands that are too small.
 */
bool NetEBBits::set_width(unsigned w, bool)
{
	/* First, give the operands a chance to adjust themselves to
	   the requested width. */
      left_->set_width(w);
      right_->set_width(w);


	/*  */

      unsigned use_width = w;
      if (left_->expr_width() > use_width)
	    use_width = left_->expr_width();
      if (right_->expr_width() > use_width)
	    use_width = right_->expr_width();

	/* If the operands end up too small, then pad them to suit. */

      if (left_->expr_width() < use_width) {
	    NetExpr*tmp = pad_to_width(left_, use_width, *this);
	    assert(tmp);
	    left_ = tmp;
      }

      if (right_->expr_width() < w) {
	    NetExpr*tmp = pad_to_width(right_, use_width, *this);
	    assert(tmp);
	    right_ = tmp;
      }


	/* And here is the final width. If this is not the size the
	   caller requested, then return false. Otherwise, return
	   true. */
      expr_width(use_width);
      return w == use_width;
}

/*
 * Comparison operators allow the subexpressions to have
 * their own natural width, but the comparison operator result has a
 * fixed width of 1.
 */
bool NetEBComp::set_width(unsigned w, bool)
{
      return (w == 1);
}

/*
 * There is nothing we can do to the operands of a division to make it
 * confirm to the requested width. Force the context to pad or truncate.
 */
bool NetEBDiv::set_width(unsigned w, bool)
{
      return w == expr_width();
}

bool NetEBLogic::set_width(unsigned w, bool)
{
      bool flag;
      flag = left_->set_width(right_->expr_width());
      if (!flag)
	    flag = right_->set_width(left_->expr_width());
      return (w == 1);
}

/*
 * There is nothing we can do to the operands of a multiply to make it
 * confirm to the requested width. Force the context to pad or truncate.
 */
bool NetEBMult::set_width(unsigned w, bool)
{
      if (w < left_->expr_width())
	    left_->set_width(w);
      if (w < right_->expr_width())
	    right_->expr_width();

      expr_width(w);
      return true;
}

bool NetEBPow::set_width(unsigned w, bool last_chance)
{
      return w == expr_width();
}

/*
 * The shift operator allows the shift amount to have its own
 * natural width. The width of the operator result is the width of the
 * left operand, the value that is to be shifted.
 */
bool NetEBShift::set_width(unsigned w, bool)
{
      bool flag = true;

      switch (op()) {

	  case 'l':
	    left_->set_width(w);
	    if (left_->expr_width() < w)
		  left_ = pad_to_width(left_, w, *this);
	    break;

	  case 'r':
	  case 'R':
	    if (left_->expr_width() < w)
		  left_ = pad_to_width(left_, w, *this);
	    break;

	  default:
	    assert(0);
      }

      expr_width(left_->expr_width());
      flag = expr_width() == w;

      return flag;
}

/*
 * Add up the widths from all the expressions that are concatenated
 * together. This is the width of the expression, tough luck if you
 * want it otherwise.
 *
 * If during the course of elaboration one of the sub-expressions is
 * broken, then don't count it in the width. This doesn't really
 * matter because the null expression is indication of an error and
 * the compiler will not go beyond elaboration.
 */
bool NetEConcat::set_width(unsigned w, bool)
{
      unsigned sum = 0;
      for (unsigned idx = 0 ;  idx < parms_.count() ;  idx += 1)
	    if (parms_[idx] != 0)
		  sum += parms_[idx]->expr_width();

      sum *= repeat();
      expr_width(sum);
      if (sum != w) return false;
      return true;
}

bool NetEConst::set_width(unsigned w, bool last_chance)
{
       /* Make the value signed if the NetEConst is signed.
        * This happens when $signed() is called, so this
        * sign information needs to be propagated. */
      value_.has_sign(has_sign());

      if (w == value_.len()) {
	    expr_width(w);
	    return true;
      }

      assert(w != 0);

      if (w > value_.len()) {
	    verinum::V pad = verinum::V0;
	    if (value_.has_sign()) {
		  pad = value_.get(value_.len()-1);

	      /* It appears that you always have a defined length here,
	       * so this logic may be in error. */
	    } else if (value_.len() != 0 && !value_.has_len())
	      switch (value_.get(value_.len()-1)) {
		case verinum::V1:
		case verinum::V0:
		  break;
		case verinum::Vx:
		  pad = verinum::Vx;
		  break;
		case verinum::Vz:
		  pad = verinum::Vz;
		  break;
	    }

	    verinum tmp (verinum::V0, w, has_width());
	    for (unsigned idx = 0 ;  idx < value_.len() ;  idx += 1)
		  tmp.set(idx, value_[idx]);
	    for (unsigned idx = value_.len() ;  idx < w  ; idx += 1)
		  tmp.set(idx, pad);

	    tmp.has_sign(value_.has_sign());
	    value_ = tmp;

	    expr_width(w);
	    return true;

      } else {
	    unsigned use_w = w;

	    verinum::V pad_bit = value_.has_sign()
		  ? value_[value_.len() - 1]
		  : verinum::V0;

	    if (! last_chance) {
		    // Don't reduce a number too small to hold all the
		    // significant bits.
		  for (unsigned idx = w ;  idx < value_.len() ;  idx += 1)
			if (value_[idx] != pad_bit)
			      use_w = idx+1;

		    // Correct for the special case of signed value. We
		    // cannot have the result change sign on us.
		  if (value_.has_sign() && (use_w < value_.len())
		      && (value_[use_w-1] != pad_bit))
			use_w += 1;
	    }

	    verinum tmp (verinum::V0, use_w, has_width());
	    for (unsigned idx = 0 ;  idx < use_w ;  idx += 1)
		  tmp.set(idx, value_[idx]);

	    tmp.has_sign(value_.has_sign());
	    value_ = tmp;
	    expr_width(use_w);
	    return use_w == w;
      }
}

void NetEConst::cast_signed(bool sign_flag)
{
      value_.has_sign(sign_flag);
      cast_signed_base_(sign_flag);
}

/*
 * Parameter vectors cannot be resized because they refer to a common
 * value.
 */
bool NetEConstParam::set_width(unsigned w, bool)
{
      return w == expr_width();
}

/*
 * Real constants can have whatever width the environment wants,
 * because it isn't really a vector. The environment will convert this
 * to a vector at the right time.
 */
bool NetECReal::set_width(unsigned w, bool)
{
      expr_width(w);
      return true;
}
#if 0
bool NetEMemory::set_width(unsigned w, bool)
{
      if (w != mem_->width())
	    return false;

      expr_width(w);
      return true;
}
#endif
bool NetEParam::set_width(unsigned, bool)
{
      return false;
}

bool NetESelect::set_width(unsigned w, bool)
{
      if (expr_width() == 1)
	    return true;
      else
	    return false;
}

bool NetESFunc::set_width(unsigned w, bool)
{
      return w == expr_width();
}

/*
 * The signal should automatically pad with zeros to get to the desired
 * width. Do not allow signal bits to be truncated, however.
 */
bool NetESignal::set_width(unsigned w, bool)
{
      if (w != vector_width())
	    return false;

      return true;
}

bool NetETernary::set_width(unsigned w, bool last_chance)
{
      bool flag = true;
      flag = flag && true_val_->set_width(w, last_chance);
      flag = flag && false_val_->set_width(w, last_chance);

	/* The ternary really insists that the true and false clauses
	   have the same width. Even if we fail to make the width that
	   the user requests, at least pad the smaller width to suit
	   the larger. */
      if (true_val_->expr_width() < false_val_->expr_width())
	    true_val_ = pad_to_width(true_val_, false_val_->expr_width(),
	                             *this);
      if (false_val_->expr_width() < true_val_->expr_width())
	    false_val_ = pad_to_width(false_val_, true_val_->expr_width(),
	                             *this);

      expr_width(true_val_->expr_width());
      return flag;
}

/*
 * XXXX FIX ME: For now, just take whatever the caller says as my
 * width. What I really need to do is note the width of the output
 * parameter of the function definition and take that into account.
 */
bool NetEUFunc::set_width(unsigned wid, bool)
{
      if (result_sig_->expr_width() == wid)
	    return true;
      else
	    return false;
}

bool NetEUnary::set_width(unsigned w, bool)
{
      bool flag = true;
      switch (op_) {
	  case '~':
	  case '-':
	    flag = expr_->set_width(w);
	    expr_width(w);
	    break;
	  case '!':
	    return w == 1;
	  default:
	    flag = expr_width() == w;
	    break;
      }

      return flag;
}

/*
 * Unary reduction operators allow its operand to have any width. The
 * result is defined to be 1.
 */
bool NetEUReduce::set_width(unsigned w, bool)
{
      return w == 1;
}