misc.c

/*
 * Copyright (C) 2011-2022 Cary R. (cygcary@yahoo.com)
 *
 *  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.,
 *  51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
 */

# include <ctype.h>
# include <stdlib.h>
# include <string.h>
# include "config.h"
# include "vlog95_priv.h"
# include "ivl_alloc.h"

/*
 * Emit a constant delay that has been rescaled to the given scopes timescale.
 */
void emit_scaled_delay(ivl_scope_t scope, uint64_t delay)
{
      int scale = ivl_scope_time_units(scope) - sim_precision;
      int pre = ivl_scope_time_units(scope) - ivl_scope_time_precision(scope);
      char *frac;
      unsigned real_dly = 0;
      assert(scale >= 0);
      assert(pre >= 0);
      assert(scale >= pre);
      frac = (char *)malloc(pre+1);
      frac[pre] = 0;
      for (/* none */; scale > 0; scale -= 1) {
	    if (scale > pre) {
		  assert((delay % 10) == 0);
	    } else {
		  frac[scale-1] = (delay % 10) + '0';
		  if (frac[scale-1] != '0') {
			real_dly = 1;
		  } else if (!real_dly) {
			frac[scale-1] = 0;
		  }
	    }
	    delay /= 10;
      }
      if (real_dly) {
	    fprintf(vlog_out, "%"PRIu64".%s", delay, frac);
      } else {
	    if (delay & 0xffffffff80000000) {
		  fprintf(vlog_out, "(64'd%"PRIu64")", delay);
	    } else {
		  fprintf(vlog_out, "%"PRIu64, delay);
	    }
      }
      free(frac);
}

static void emit_delay(ivl_scope_t scope, ivl_expr_t expr, unsigned is_stmt)
{
	/* A delay in a continuous assignment can also be a continuous
	 * assignment expression. */
      if (ivl_expr_type(expr) == IVL_EX_SIGNAL) {
	    ivl_signal_t sig = ivl_expr_signal(expr);
	    if (ivl_signal_local(sig)) {
		  assert(! is_stmt);
		  emit_nexus_as_ca(scope, ivl_signal_nex(sig, 0), 0, 0);
		  return;
	    }
      }
      emit_expr(scope, expr, 0, 0, 0, 1);
}

/*
 * Check to see if the bit based expression is of the form (expr) * <scale>
 */
static unsigned check_scaled_expr(ivl_expr_t expr, uint64_t scale,
                                  const char *msg, unsigned must_match)
{
      uint64_t scale_val;
      int rtype;
      if ((ivl_expr_type(expr) != IVL_EX_BINARY) ||
          (ivl_expr_opcode(expr) != '*') ||
          (ivl_expr_type(ivl_expr_oper2(expr)) != IVL_EX_NUMBER)) {
	    fprintf(stderr, "%s:%u: vlog95 error: %s expression/value "
	                    "cannot be scaled.\n ",
	                    ivl_expr_file(expr), ivl_expr_lineno(expr), msg);
	    vlog_errors += 1;
	    return 0;
      }
      scale_val = get_uint64_from_number(ivl_expr_oper2(expr), &rtype);
      if (rtype > 0) {
	    fprintf(stderr, "%s:%u: vlog95 error: %s expression/value "
	                    "scale coefficient was greater than 64 bits "
	                    "(%d).\n", ivl_expr_file(expr),
	                    ivl_expr_lineno(expr), msg, rtype);
	    vlog_errors += 1;
	    return 0;
      }
      if (rtype < 0) {
	    fprintf(stderr, "%s:%u: vlog95 error: %s expression/value "
	                    "scale coefficient has an undefined bit.\n",
	                    ivl_expr_file(expr), ivl_expr_lineno(expr), msg);
	    vlog_errors += 1;
	    return 0;
      }
      if (scale != scale_val) {
	    if (must_match) {
		  fprintf(stderr, "%s:%u: vlog95 error: %s expression/value "
		                  "scale coefficient did not match expected "
		                  "value (%"PRIu64" != %"PRIu64").\n",
		                  ivl_expr_file(expr), ivl_expr_lineno(expr),
		                  msg, scale, scale_val);
		  vlog_errors += 1;
		  return 0;
	    }
	    return 2;
      }
	/* Yes, this expression is of the correct form. */
      return 1;
}

/*
 * Check to see if the real expression is of the form (expr) * <scale>
 */
static unsigned check_scaled_real_expr(ivl_expr_t expr, double scale)
{
      double scale_val;
      if ((ivl_expr_type(expr) != IVL_EX_BINARY) ||
          (ivl_expr_opcode(expr) != '*') ||
          (ivl_expr_type(ivl_expr_oper2(expr)) != IVL_EX_REALNUM)) {
	    fprintf(stderr, "%s:%u: vlog95 error: Variable real time unit "
	                    " expression/value cannot be scaled.\n ",
	                    ivl_expr_file(expr), ivl_expr_lineno(expr));
	    vlog_errors += 1;
	    return 0;
      }
      scale_val = ivl_expr_dvalue(ivl_expr_oper2(expr));
      if (scale != scale_val) {
	    fprintf(stderr, "%s:%u: vlog95 error: Variable real time unit "
	                    "expression/value scale coefficient did not "
	                    "match expected value (%g != %g).\n",
	                    ivl_expr_file(expr), ivl_expr_lineno(expr),
	                    scale, scale_val);
	    vlog_errors += 1;
	    return 0;
      }
	/* Yes, this expression is of the correct form. */
      return 1;
}

/*
 * Emit a constant or variable delay that has been rescaled to the given
 * scopes timescale.
 */
void emit_scaled_delayx(ivl_scope_t scope, ivl_expr_t expr, unsigned is_stmt)
{
      ivl_expr_type_t type = ivl_expr_type(expr);
      if (type == IVL_EX_DELAY) {
	    emit_scaled_delay(scope, ivl_expr_delay_val(expr));
      } else if (type == IVL_EX_NUMBER) {
	    assert(! ivl_expr_signed(expr));
	    int rtype;
	    uint64_t value = get_uint64_from_number(expr, &rtype);
	    if (rtype > 0) {
		  fprintf(vlog_out, "<invalid>");
		  fprintf(stderr, "%s:%u: vlog95 error: Time value is "
		                  "greater than 64 bits (%d) and cannot be "
		                  "safely represented.\n",
		                  ivl_expr_file(expr), ivl_expr_lineno(expr),
		                  rtype);
		  vlog_errors += 1;
		  return;
	    }
	    if (rtype < 0) {
		  fprintf(vlog_out, "<invalid>");
		  fprintf(stderr, "%s:%u: vlog95 error: Time value has an "
		                  "undefined bit and cannot be represented.\n",
		                  ivl_expr_file(expr), ivl_expr_lineno(expr));
		  vlog_errors += 1;
		  return;
	    }
	    emit_scaled_delay(scope, value);
      } else {
	    int exponent = ivl_scope_time_units(scope) - sim_precision;
	    assert(exponent >= 0);
	    if ((exponent == 0) && (type == IVL_EX_SIGNAL)) {
		  emit_delay(scope, expr, is_stmt);
	      /* A real delay variable is not scaled by the compiler. */
	    } else if (type == IVL_EX_SIGNAL) {
		  if (is_stmt) {
			fprintf(vlog_out, "<invalid>");
			fprintf(stderr, "%s:%u: vlog95 error: Only continuous "
			                "assignment delay variables are scaled "
			                "at run time.\n", ivl_expr_file(expr),
			                ivl_expr_lineno(expr));
			vlog_errors += 1;
			return;
		  }
		  emit_delay(scope, expr, is_stmt);
	    } else {
		  uint64_t iscale = 1;
		  unsigned rtn;
		  assert(! ivl_expr_signed(expr));
		    /* Calculate the integer time scaling coefficient. */
		  while (exponent > 0) {
			iscale *= 10;
			exponent -= 1;
		  }
		    /* Check to see if this is an integer time value. */
		  rtn = check_scaled_expr(expr, iscale, "Variable time", 0);
		    /* This may be a scaled real value. */
		  if (rtn == 2){
			ivl_expr_t tmp_expr;
			uint64_t rprec = 1;
			  /* This could be a scaled real time so calculate
			   * the real time scaling coefficients and check
			   * that the expression matches (statements only). */
			exponent = ivl_scope_time_precision(scope) -
			           sim_precision;
			assert(exponent >= 0);
			while (exponent > 0) {
			      rprec *= 10;
			      exponent -= 1;
			}
			  /* Verify that the precision scaling is correct. */
			if (! check_scaled_expr(expr, rprec,
			                        "Variable real time prec.",
			                        1)) {
			      fprintf(vlog_out, "<invalid>");
			      return;
			}
			  /* Verify that the left operator is a real to
			   * integer cast. */
			tmp_expr = ivl_expr_oper1(expr);
			if ((ivl_expr_type(tmp_expr) != IVL_EX_UNARY) ||
		            (ivl_expr_opcode(tmp_expr) != 'v')) {
			      fprintf(vlog_out, "<invalid>");
			      fprintf(stderr, "%s:%u: vlog95 error: Real time "
			                      "value does not have a cast to "
			                      "integer.\n",
			                      ivl_expr_file(expr),
			                      ivl_expr_lineno(expr));
			      vlog_errors += 1;
			      return;
			}
			  /* Check that the cast value is scaled correctly. */
			assert(iscale >= rprec);
			tmp_expr = ivl_expr_oper1(tmp_expr);
			assert(ivl_expr_value(tmp_expr) == IVL_VT_REAL);
			if (! check_scaled_real_expr(tmp_expr, iscale/rprec)) {
			      fprintf(vlog_out, "<invalid>");
			      return;
			}
			assert(is_stmt);
			emit_delay(scope, ivl_expr_oper1(tmp_expr), is_stmt);
			return;
		  } else if (rtn == 1) {
			emit_delay(scope, ivl_expr_oper1(expr), is_stmt);
			return;
		  }
		  fprintf(vlog_out, "<invalid>");
	    }
      }
}

static int64_t get_valid_int64_from_number(ivl_expr_t expr, int *rtype,
                                           const char *msg)
{
      int64_t value = get_int64_from_number(expr, rtype);
      if (*rtype > 0) {
	    fprintf(vlog_out, "<invalid>");
	    fprintf(stderr, "%s:%u: vlog95 error: Scaled %s is greater than "
	                    "64 bits (%d) and cannot be safely represented.\n",
	                    ivl_expr_file(expr), ivl_expr_lineno(expr),
	                    msg, *rtype);
	    vlog_errors += 1;
      } else if (*rtype < 0) {
	    fprintf(vlog_out, "<invalid>");
	    fprintf(stderr, "%s:%u: vlog95 error: Scaled %s has an undefined "
	                    "bit and cannot be represented.\n",
	                    ivl_expr_file(expr), ivl_expr_lineno(expr), msg);
	    vlog_errors += 1;
      }
      return value;
}

// HERE: Probably need to pass in a msg string to make this work with
//       indexed part selects.
static unsigned is_scaled_expr(ivl_expr_t expr, int msb, int lsb)
{
      int64_t scale_val;
      int rtype;
	/* This is as easy as removing the addition/subtraction that was
	 * added to scale the value to be zero based, but we need to verify
	 * that the scaling value is correct first. */
      if (msb > lsb) {
	    if ((ivl_expr_type(expr) != IVL_EX_BINARY) ||
	        ((ivl_expr_opcode(expr) != '+') &&
	         (ivl_expr_opcode(expr) != '-')) ||
	        (ivl_expr_type(ivl_expr_oper2(expr)) != IVL_EX_NUMBER)) {
		  fprintf(vlog_out, "<invalid>");
		  fprintf(stderr, "%s:%u: vlog95 error: Scaled "
		                  "expression value cannot be scaled.\n",
		                  ivl_expr_file(expr),
		                  ivl_expr_lineno(expr));
		  vlog_errors += 1;
		  return 0;
	    }
	    scale_val = get_valid_int64_from_number(
	                      ivl_expr_oper2(expr), &rtype,
	                      "expression value scale coefficient");
      } else {
	    if ((ivl_expr_type(expr) != IVL_EX_BINARY) ||
	        ((ivl_expr_opcode(expr) != '+') &&
	         (ivl_expr_opcode(expr) != '-')) ||
	        (ivl_expr_type(ivl_expr_oper1(expr)) != IVL_EX_NUMBER)) {
		  fprintf(vlog_out, "<invalid>");
		  fprintf(stderr, "%s:%u: vlog95 error: Scaled "
		                  "expression value cannot be scaled.\n",
		                  ivl_expr_file(expr),
		                  ivl_expr_lineno(expr));
		  vlog_errors += 1;
		  return 0;
	    }
	    scale_val = get_valid_int64_from_number(
	                      ivl_expr_oper1(expr), &rtype,
	                      "expression value scale coefficient");
      }
      if (rtype) return 0;
      if (ivl_expr_opcode(expr) == '+') scale_val *= -1;
      if (lsb !=  scale_val) {
	    fprintf(vlog_out, "<invalid>");
	    fprintf(stderr, "%s:%u: vlog95 error: Scaled expression value "
	                    "scaling coefficient did not match expected "
	                    "value (%d != %"PRIu64").\n",
	                    ivl_expr_file(expr), ivl_expr_lineno(expr),
	                    lsb, scale_val);
	    vlog_errors += 1;
	    return 0;
      }
      return 1;
}

static int64_t get_in_range_int64_from_number(ivl_expr_t expr, int *rtype,
                                              const char *msg)
{
      int64_t value = get_int64_from_number(expr, rtype);
      if (*rtype > 0) {
	    fprintf(vlog_out, "<invalid>");
	    fprintf(stderr, "%s:%u: vlog95 error: Scaled %s is greater than "
	                    "64 bits (%d) and cannot be safely represented.\n",
	                    ivl_expr_file(expr), ivl_expr_lineno(expr),
	                    msg, *rtype);
	    vlog_errors += 1;
      }
      return value;
}

void emit_scaled_range(ivl_scope_t scope, ivl_expr_t expr, unsigned width,
                       int msb, int lsb)
{
      int rtype;
      int64_t value = get_in_range_int64_from_number(expr, &rtype,
                                                     "range value");
      (void)scope;  /* Parameter is not used. */
      if (rtype < 0) fprintf(vlog_out, "[1'bx:1'bx]");
      if (rtype) return;

      if (msb >= lsb) {
	    value += lsb;
	    fprintf(vlog_out, "[%"PRId64":%"PRId64"]",
	                      value + (int64_t)(width - 1), value);
      } else {
	    value = (int64_t)lsb - value;
	    fprintf(vlog_out, "[%"PRId64":%"PRId64"]",
	                      value - (int64_t)(width - 1), value);
      }
}

void emit_scaled_expr(ivl_scope_t scope, ivl_expr_t expr, int msb, int lsb)
{
      if (msb >= lsb) {
	    if (ivl_expr_type(expr) == IVL_EX_NUMBER) {
		  int rtype;
		  int64_t value = get_in_range_int64_from_number(expr, &rtype,
		                                                 "value");
		  if (rtype < 0) fprintf(vlog_out, "1'bx");
		  if (rtype) return;
		  value += lsb;
		  fprintf(vlog_out, "%"PRId64, value);
	    } else if (lsb == 0) {
		    /* If the LSB is zero then there is no scale. */
		  emit_expr(scope, expr, 0, 0, 0, 1);
	    } else {
		  if (is_scaled_expr(expr, msb, lsb)) {
			emit_expr(scope, ivl_expr_oper1(expr), 0, 0, 0, 1);
		  }
	    }
      } else {
	    if (ivl_expr_type(expr) == IVL_EX_NUMBER) {
		  int rtype;
		  int64_t value = get_in_range_int64_from_number(expr, &rtype,
		                                                 "value");
		  if (rtype < 0) fprintf(vlog_out, "1'bx");
		  if (rtype) return;
		  value = (int64_t)lsb - value;
		  fprintf(vlog_out, "%"PRId64, value);
	    } else {
		  if (is_scaled_expr(expr, msb, lsb)) {
			emit_expr(scope, ivl_expr_oper2(expr), 0, 0, 0, 1);
		  }
	    }
      }
}

static unsigned find_signal_in_nexus(const ivl_scope_t scope, ivl_nexus_t nex)
{
      ivl_signal_t use_sig = 0;
      unsigned is_driver = 0;
      unsigned is_array = 0;
      int64_t array_idx = 0;
      unsigned idx, count = ivl_nexus_ptrs(nex);

      for (idx = 0; idx < count; idx += 1) {
	    ivl_nexus_ptr_t nex_ptr = ivl_nexus_ptr(nex, idx);
	    ivl_signal_t sig = ivl_nexus_ptr_sig(nex_ptr);
	    if (! sig) continue;
	    if (ivl_signal_local(sig)) {
		    /* If the local signal is another receiver skip it. */
		  if ((ivl_nexus_ptr_drive1(nex_ptr) == IVL_DR_HiZ) &&
		      (ivl_nexus_ptr_drive0(nex_ptr) == IVL_DR_HiZ)) {
			continue;
		  }
	          assert(0);
	    }
	      /* We have a signal that can be used to find the name. */
	    if (scope == ivl_signal_scope(sig)) {
		  if (use_sig) {
			  /* Swap a receiver for a driver. */
			if (is_driver &&
			    (ivl_nexus_ptr_drive1(nex_ptr) == IVL_DR_HiZ) &&
			    (ivl_nexus_ptr_drive0(nex_ptr) == IVL_DR_HiZ)) {
			      use_sig = sig;
			      is_driver = 0;
			      if (ivl_signal_dimensions(sig) > 0) {
				    is_array = 1;
				    array_idx = ivl_nexus_ptr_pin(nex_ptr);
				    array_idx += ivl_signal_array_base(sig);
			      }
			      continue;
			}
// HERE: Which one should we use? For now it's the first one found.
//       I believe this needs to be solved (see the inout.v test).
			fprintf(stderr, "%s:%u: vlog95 warning: Duplicate "
			                "name (%s",
			                ivl_signal_file(sig),
			                ivl_signal_lineno(sig),
			                ivl_signal_basename(sig));
			if (ivl_signal_dimensions(sig) > 0) {
			      int64_t tmp_idx = ivl_nexus_ptr_pin(nex_ptr);
			      tmp_idx += ivl_signal_array_base(sig);
			      fprintf(stderr, "[%"PRId64"]", tmp_idx);
			}
			fprintf(stderr, ") found for nexus (%s",
			                ivl_signal_basename(use_sig));
			if (is_array) fprintf(stderr, "[%"PRId64"]", array_idx);
			fprintf(stderr, ")\n");
		  } else {
			use_sig = sig;
			  /* This signal is a driver. */
			if ((ivl_nexus_ptr_drive1(nex_ptr) != IVL_DR_HiZ) ||
			    (ivl_nexus_ptr_drive0(nex_ptr) != IVL_DR_HiZ)) {
			      is_driver = 1;
			}
			if (ivl_signal_dimensions(sig) > 0) {
			      is_array = 1;
			      array_idx = ivl_nexus_ptr_pin(nex_ptr);
			      array_idx += ivl_signal_array_base(sig);
			}
		  }
	    }
      }

      if (use_sig) {
	    emit_id(ivl_signal_basename(use_sig));
	    if (is_array) fprintf(vlog_out, "[%"PRId64"]", array_idx);
	    return 1;
      }

      return 0;
}

static void emit_number_as_string(ivl_net_const_t net_const)
{
      const char *bits = ivl_const_bits(net_const);
      unsigned count = ivl_const_width(net_const);
      int idx;

      assert((count % 8) == 0);
      fprintf(vlog_out, "\"");
      for (idx = (int)count-1; idx >= 0; idx -= 8) {
	    unsigned bit;
	    char val = 0;
	    for (bit = 0; bit < 8; bit += 1) {
		  val |= (bits[idx-bit] == '1') ?  1 << (7-bit) : 0x00;
	    }

	      /* Print some values that can be escaped. */
	    if (val == '"') fprintf(vlog_out, "\\\"");
	    else if (val == '\\') fprintf(vlog_out, "\\\\");
	    else if (val == '\n') fprintf(vlog_out, "\\n");
	    else if (val == '\t') fprintf(vlog_out, "\\t");
	      /* Print the printable characters. */
	    else if (isprint((int)val)) fprintf(vlog_out, "%c", val);
	      /* Print the non-printable characters as an octal escape. */
	    else fprintf(vlog_out, "\\%03o", val);
      }
      fprintf(vlog_out, "\"");
}

static unsigned emit_as_input(ivl_scope_t scope, ivl_net_const_t net_const)
{
      ivl_scope_t const_scope = ivl_const_scope(net_const);
      ivl_scope_t parent = ivl_scope_parent(scope);

	/* Look to see if the constant scope is a parent of this scope. */
      while (parent) {
	    if (parent == const_scope) break;
	    parent = ivl_scope_parent(parent);
      }

	/* If the constant scope is a parent then look for an input in
	 * this scope and use that for the name. */
      if (parent) {
	    ivl_nexus_t nex = ivl_const_nex(net_const);
	    unsigned idx, count = ivl_nexus_ptrs(nex);
	    for (idx = 0; idx < count; idx += 1) {
		  ivl_nexus_ptr_t nex_ptr = ivl_nexus_ptr(nex, idx);
		  ivl_signal_t sig = ivl_nexus_ptr_sig(nex_ptr);
		  if (sig && (ivl_signal_port(sig) == IVL_SIP_INPUT)) {
			emit_id(ivl_signal_basename(sig));
			return 1;
		  }
	    }
      }

      return 0;
}

void emit_const_nexus(ivl_scope_t scope, ivl_net_const_t net_const)
{
      ivl_scope_t const_scope = ivl_const_scope(net_const);
      unsigned idx, count, lineno;
      const char *file;
      count = ivl_scope_params(const_scope);
      file = ivl_const_file(net_const);
      lineno = ivl_const_lineno(net_const);
	/* Look to see if the constant matches a parameter in its scope. */
      for (idx = 0; idx < count; idx += 1) {
	    ivl_parameter_t par = ivl_scope_param(const_scope, idx);
	    if (lineno != ivl_parameter_lineno(par)) continue;
	    if (strcmp(file, ivl_parameter_file(par)) == 0) {
		    /* Check that the appropriate expression bits match the
		     * original parameter bits. */
// HERE: Verify that the values match and then print the name.
//       Does this work with out of scope references? Check real parameters.
		  emit_id(ivl_parameter_basename(par));
		  return;
	    }
      }

	/* If the scopes don't match then we assume this is an empty port. */
      if (const_scope != scope)  {
	      /* This constant could really be from an input port. */
	    if (emit_as_input(scope, net_const)) return;
	    fprintf(vlog_out, "/* Empty */");
	    return;
      }

      switch (ivl_const_type(net_const)) {
	case IVL_VT_LOGIC:
	case IVL_VT_BOOL:
	    emit_number(ivl_const_bits(net_const),
	                ivl_const_width(net_const),
	                ivl_const_signed(net_const),
	                ivl_const_file(net_const),
	                ivl_const_lineno(net_const));
	    break;
	case IVL_VT_STRING:
	    emit_number_as_string(net_const);
	    break;
	case IVL_VT_REAL:
	    emit_real_number(ivl_const_real(net_const));
	    break;
	default:
	    fprintf(vlog_out, "<invalid>");
	    fprintf(stderr, "%s:%u: vlog95 error: Unknown constant type "
	                    "(%d).\n",
	                    ivl_const_file(net_const),
	                    ivl_const_lineno(net_const),
	                    (int)ivl_const_type(net_const));
	    vlog_errors += 1;
	    break;
      }
}

static unsigned find_const_nexus(ivl_scope_t scope, ivl_nexus_t nex)
{
      unsigned idx, count;

      count = ivl_nexus_ptrs(nex);
      for (idx = 0; idx < count; idx += 1) {
	    ivl_nexus_ptr_t nex_ptr = ivl_nexus_ptr(nex, idx);
	    ivl_net_const_t net_const = ivl_nexus_ptr_con(nex_ptr);
// HERE: Do we need to check for duplicates?
	    if (net_const) {
		  assert(! ivl_nexus_ptr_pin(nex_ptr));
		  emit_const_nexus(scope, net_const);
		  return 1;
	    }
      }
      return 0;
}

static unsigned find_driving_signal(ivl_scope_t scope, ivl_nexus_t nex)
{
      ivl_signal_t sig = 0;
      unsigned is_array = 0;
      int64_t array_idx = 0;
      unsigned idx, count = ivl_nexus_ptrs(nex);

      for (idx = 0; idx < count; idx += 1) {
	    ivl_nexus_ptr_t nex_ptr = ivl_nexus_ptr(nex, idx);
	    ivl_signal_t t_sig = ivl_nexus_ptr_sig(nex_ptr);
	    if (! t_sig) continue;
	    if (ivl_signal_local(t_sig)) continue;
	      /* An output can be used if it is driven by this nexus. */
	    if ((ivl_nexus_ptr_drive1(nex_ptr) == IVL_DR_HiZ) &&
	        (ivl_nexus_ptr_drive0(nex_ptr) == IVL_DR_HiZ) &&
	        (ivl_signal_port(t_sig) != IVL_SIP_OUTPUT)) {
		  continue;
	    }
	      /* We have a signal that can be used to find the name. */
	    if (sig) {
// HERE: Which one should we use? For now it's the first one found.
//       I believe this needs to be solved (see above).
		  fprintf(stderr, "%s:%u: vlog95 warning: Duplicate name (%s",
		          ivl_signal_file(t_sig), ivl_signal_lineno(t_sig),
		          ivl_signal_basename(t_sig));
		  if (ivl_signal_dimensions(t_sig) > 0) {
			int64_t tmp_idx = ivl_nexus_ptr_pin(nex_ptr);
			tmp_idx += ivl_signal_array_base(t_sig);
			fprintf(stderr, "[%"PRId64"]", tmp_idx);
		  }
		  fprintf(stderr, ") found for nexus (%s",
		          ivl_signal_basename(sig));
		  if (is_array) fprintf(stderr, "[%"PRId64"]", array_idx);
		  fprintf(stderr, ")\n");
	    } else {
		  sig = t_sig;
		  if (ivl_signal_dimensions(sig) > 0) {
			is_array = 1;
			array_idx = ivl_nexus_ptr_pin(nex_ptr);
			array_idx += ivl_signal_array_base(sig);
		  }
	    }
      }

      if (sig) {
	    emit_scope_call_path(scope, ivl_signal_scope(sig));
	    emit_id(ivl_signal_basename(sig));
	    if (is_array) fprintf(vlog_out, "[%"PRId64"]", array_idx);
	    return 1;
      }

      return 0;
}

static unsigned is_local_input(ivl_scope_t scope, ivl_nexus_t nex)
{
      ivl_signal_t sig = 0;
      unsigned idx, count = ivl_nexus_ptrs(nex);

      (void)scope;  /* Parameter is not used. */
      for (idx = 0; idx < count; idx += 1) {
	    ivl_nexus_ptr_t nex_ptr = ivl_nexus_ptr(nex, idx);
	    ivl_signal_t t_sig = ivl_nexus_ptr_sig(nex_ptr);
	    if (! t_sig) continue;
	    if (! ivl_signal_local(t_sig)) continue;
	    if (ivl_signal_port(t_sig) != IVL_SIP_INPUT) continue;
	    assert(! sig);
	    assert(ivl_signal_dimensions(t_sig) == 0);
	    sig = t_sig;
      }
      if (sig) {
	    fprintf(vlog_out, "ivlog%s", ivl_signal_basename(sig));
	    return 1;
      }
      return 0;
}

// HERE: Does this work correctly with an array reference created from @*?
void emit_name_of_nexus(ivl_scope_t scope, ivl_nexus_t nex, unsigned allow_UD)
{
      unsigned idx;

      ivl_scope_t mod_scope;
	/* First look in the local scope for the nexus name. */
      if (find_signal_in_nexus(scope, nex)) return;

	/* If the signal was not found in the passed scope then look in
	 * the module scope if the passed scope was not the module scope. */
      mod_scope = get_module_scope(scope);
      if (mod_scope != scope) {
	    if (find_signal_in_nexus(mod_scope, nex)) return;
      }

	/* Look to see if this is a up/down reference. */
      if (allow_UD && find_driving_signal(scope, nex)) return;

	/* If there is no signals driving this then look for a constant. */
      if (find_const_nexus(scope, nex)) return;

	/* Module inputs that are split (arg[7:4], arg[3:0]) need to use
	 * the local signal names. */
      if (is_local_input(scope, nex)) return;

// HERE: Need to check arr[var]? Can this be rebuilt?
//       Then look for down scopes and then any scope. For all this warn if
//       multiples are found in a given scope. This all needs to be before
//       the constant code.

	/* It is possible that the nexus does not have a name. First check
	   if it drives another nexus through a transparent buffer. */
      for (idx = 0; idx < ivl_nexus_ptrs(nex); idx += 1) {
	    ivl_nexus_ptr_t nex_ptr = ivl_nexus_ptr(nex, idx);
	    ivl_net_logic_t nlogic = ivl_nexus_ptr_log(nex_ptr);
	    if (nlogic && ivl_logic_type(nlogic) == IVL_LO_BUFT
		&& ivl_logic_pin(nlogic, 1) == nex) {
		  emit_name_of_nexus(scope, ivl_logic_pin(nlogic, 0), allow_UD);
		  return;
	    }
      }

	/* If not, do not print an actual name. */
      fprintf(vlog_out, "/* Empty */");
//      dump_nexus_information(scope, nex);
}

/*
 * This function traverses the scope tree looking for the enclosing module
 * scope. When it is found the module scope is returned. As far as this
 * translation is concerned a package is a special form of a module
 * definition and a class is also a top level scope. In SystemVerilog,
 * tasks and functions can also be top level scopes - we create a wrapper
 * module for these later.
 */
ivl_scope_t get_module_scope(ivl_scope_t scope)
{

      while ((ivl_scope_type(scope) != IVL_SCT_MODULE) &&
             (ivl_scope_type(scope) != IVL_SCT_PACKAGE) &&
             (ivl_scope_type(scope) != IVL_SCT_CLASS)) {
	    ivl_scope_t pscope = ivl_scope_parent(scope);
	    if (pscope == 0) {
		  if (ivl_scope_type(scope) == IVL_SCT_TASK)
			break;
		  if (ivl_scope_type(scope) == IVL_SCT_FUNCTION)
			break;
	    }
	    assert(pscope);
	    scope = pscope;
      }
      return scope;
}

/*
 * A package is emitted as a module with a special name. This routine
 * calculates the name for the package. The returned string must be freed
 * by the calling routine.
 */
char * get_package_name(ivl_scope_t scope)
{
      char *package_name;
      const char *name = ivl_scope_basename(scope);
      package_name = (char *)malloc(strlen(name)+13);
      strcpy(package_name, "ivl_package_");
      strcat(package_name, name);
      return package_name;
}

static void emit_scope_piece(ivl_scope_t scope, ivl_scope_t call_scope)
{
      ivl_scope_t parent = ivl_scope_parent(call_scope);
	/* If we are not at the top of the scope (parent != 0) and the two
	 * scopes do not match then print the parent scope. */
      if ((parent != 0) && (scope != parent)) {
	    emit_scope_piece(scope, parent);
      }
	/* If the scope is a package then add the special part of the name. */
      if (ivl_scope_type(call_scope) == IVL_SCT_PACKAGE) {
	    char *package_name = get_package_name(call_scope);
	    emit_id(package_name);
	    free(package_name);
	/* Print the base scope. */
      } else emit_id(ivl_scope_basename(call_scope));
      fprintf(vlog_out, ".");
}

/*
 * This routine emits the appropriate string to call the call_scope from the
 * given scope. If the module scopes for the two match then do nothing. If
 * the module scopes are different, but the call_scope begins with the
 * entire module scope of scope then we can trim the top off the call_scope
 * (it is a sub-scope of the module that contains scope). Otherwise we need
 * to print the entire path of call_scope.
 */
void emit_scope_module_path(ivl_scope_t scope, ivl_scope_t call_scope)
{
      ivl_scope_t mod_scope = get_module_scope(scope);
      ivl_scope_t call_mod_scope = get_module_scope(call_scope);

      if (mod_scope == call_mod_scope) return;
      emit_scope_piece(mod_scope, call_mod_scope);
}

/* This is the same as emit_scope_module_path() except we need to add down
 * references for variables, etc. */
void emit_scope_call_path(ivl_scope_t scope, ivl_scope_t call_scope)
{
      ivl_scope_t mod_scope, call_mod_scope;

      if (scope == call_scope) return;

      mod_scope = get_module_scope(scope);
      call_mod_scope = get_module_scope(call_scope);

      if (mod_scope != call_mod_scope) {
	    emit_scope_piece(mod_scope, call_mod_scope);
      } else if (scope != call_scope) {
	    ivl_scope_t parent;
	      /* We only emit a scope path if the scope is a parent of the
	       * call scope. */
	    for (parent = ivl_scope_parent(call_scope);
	         parent != 0;
	         parent = ivl_scope_parent(parent)) {
		  if (parent == scope) {
			emit_scope_piece(scope, call_scope);
			return;
		  }
	    }
      }
}

static void emit_scope_path_piece(ivl_scope_t scope, ivl_scope_t call_scope)
{
      ivl_scope_t parent = ivl_scope_parent(call_scope);
	/* If we are not at the top of the scope (parent != 0) and the two
	 * scopes do not match then print the parent scope. */
      if ((parent != 0) && (scope != parent)) {
	    emit_scope_path_piece(scope, parent);
	    fprintf(vlog_out, ".");
      }
	/* If the scope is a package then add the special part of the name. */
      if (ivl_scope_type(call_scope) == IVL_SCT_PACKAGE) {
	    char *package_name = get_package_name(call_scope);
	    emit_id(package_name);
	    free(package_name);
	/* Print the base scope. */
      } else emit_id(ivl_scope_basename(call_scope));
}

/*
 * This routine emits the appropriate string to call the call_scope from the
 * given scope. If the module scopes for the two match then just return the
 * base name of the call_scope. If the module scopes are different, but the
 * call_scope begins with the entire module scope of scope then we can trim
 * the top off the call_scope (it is a sub-scope of the module that contains
 * scope). Otherwise we need to print the entire path of call_scope.
 */
void emit_scope_path(ivl_scope_t scope, ivl_scope_t call_scope)
{
      ivl_scope_t mod_scope, call_mod_scope;

	/* Check to see if this is a root scope task or function. */
      if (ivl_scope_parent(call_scope) == 0) {
	    fprintf(vlog_out, "ivl_root_scope_%s.",
		    ivl_scope_basename(call_scope));
	    mod_scope = 0;
	    call_mod_scope = 0;
      } else {
	    mod_scope = get_module_scope(scope);
	    call_mod_scope = get_module_scope(call_scope);
      }

      if (mod_scope == call_mod_scope) {
	    emit_id(ivl_scope_basename(call_scope));
      } else {
	    emit_scope_path_piece(mod_scope, call_scope);
      }
}

static unsigned is_escaped(const char *id)
{
      assert(id);
	/* The first digit must be alpha or '_' to be a normal id. */
      if (isalpha((int)id[0]) || id[0] == '_') {
	    unsigned idx;
	    for (idx = 1; id[idx] != '\0'; idx += 1) {
		  if (! (isalnum((int)id[idx]) ||
		         id[idx] == '_' || id[idx] == '$')) {
			return 1;
		  }
	    }
	      /* Any Verilog keyword should also be escaped. */
// HERE: Create a keyword.gperf file to do this check.
	    if ((strcmp(id, "input") == 0)  ||
	        (strcmp(id, "output") == 0) ) return 1;
	      /* We looked at all the digits, so this is a normal id. */
	    return 0;
      }
      return 1;
}

void emit_id(const char *id)
{
      if (is_escaped(id)) fprintf(vlog_out, "\\%s ", id);
      else fprintf(vlog_out, "%s", id);
}

/*
 * Get the correct MSB and LSB for a signal.
 */
void get_sig_msb_lsb(ivl_signal_t sig, int *msb, int *lsb)
{
      switch (ivl_signal_packed_dimensions(sig)) {
	  /* For a scalar we use zero for both the MSB and LSB. */
	case 0:
	    *msb = 0;
	    *lsb = 0;
	    break;
	case 1:
	  /* For a vector we use the real MSB and LSB. */
	    *msb = ivl_signal_packed_msb(sig, 0);
	    *lsb = ivl_signal_packed_lsb(sig, 0);
	    break;
	  /* For a packed vector we use the normalized MSB and LSB. */
	default:
	    *msb = ivl_signal_width(sig) - 1;
	    *lsb = 0;
	    break;
      }
}

const char*get_time_const(int time_value)
{
      switch (time_value) {
	case   2: return "100s";
	case   1: return "10s";
	case   0: return "1s";
	case  -1: return "100ms";
	case  -2: return "10ms";
	case  -3: return "1ms";
	case  -4: return "100us";
	case  -5: return "10us";
	case  -6: return "1us";
	case  -7: return "100ns";
	case  -8: return "10ns";
	case  -9: return "1ns";
	case -10: return "100ps";
	case -11: return "10ps";
	case -12: return "1ps";
	case -13: return "100fs";
	case -14: return "10fs";
	case -15: return "1fs";
	default:
	    fprintf(stderr, "Invalid time constant value %d.\n", time_value);
	    return "N/A";
      }
}