boolbv_get.cpp

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/*******************************************************************\
 
Module:
 
Author: Daniel Kroening, kroening@kroening.com
 
\*******************************************************************/
 
#include <util/arith_tools.h>
#include <util/c_types.h>
#include <util/namespace.h>
#include <util/simplify_expr.h>
#include <util/std_expr.h>
#include <util/threeval.h>
 
#include "boolbv.h"
#include "boolbv_type.h"
 
#include <algorithm>
 
exprt boolbvt::get(const exprt &expr) const
{
  if(expr.id()==ID_symbol ||
     expr.id()==ID_nondet_symbol)
  {
    const irep_idt &identifier=expr.get(ID_identifier);
 
    const auto map_entry_opt = map.get_map_entry(identifier);
 
    if(map_entry_opt.has_value())
    {
      const boolbv_mapt::map_entryt &map_entry = *map_entry_opt;
      // an input expression must either be untyped (this is used for obtaining
      // the value of clock symbols, which do not have a fixed type as the clock
      // type is computed during symbolic execution) or match the type stored in
      // the mapping
      if(expr.type() == map_entry.type)
        return bv_get_rec(expr, map_entry.literal_map, 0);
      else
      {
        PRECONDITION(expr.type() == typet{});
        exprt skeleton = expr;
        skeleton.type() = map_entry.type;
        return bv_get_rec(skeleton, map_entry.literal_map, 0);
      }
    }
  }
 
  return SUB::get(expr);
}
 
exprt boolbvt::bv_get_rec(const exprt &expr, const bvt &bv, std::size_t offset)
  const
{
  const typet &type = expr.type();
 
  if(type.id()==ID_bool)
  {
    PRECONDITION(bv.size() > offset);
    // clang-format off
    switch(prop.l_get(bv[offset]).get_value())
    {
    case tvt::tv_enumt::TV_FALSE: return false_exprt();
    case tvt::tv_enumt::TV_TRUE:  return true_exprt();
    case tvt::tv_enumt::TV_UNKNOWN: return false_exprt(); // default
    }
    // clang-format on
  }
 
  bvtypet bvtype=get_bvtype(type);
 
  if(bvtype==bvtypet::IS_UNKNOWN)
  {
    if(type.id()==ID_array)
    {
      const auto &array_type = to_array_type(type);
 
      if(is_unbounded_array(type))
        return bv_get_unbounded_array(expr);
 
      const typet &subtype = array_type.element_type();
      const auto &sub_width_opt = bv_width.get_width_opt(subtype);
 
      if(sub_width_opt.has_value() && *sub_width_opt > 0)
      {
        const std::size_t width = boolbv_width(type);
 
        std::size_t sub_width = *sub_width_opt;
 
        exprt::operandst op;
        op.reserve(width/sub_width);
 
        for(std::size_t new_offset=0;
            new_offset<width;
            new_offset+=sub_width)
        {
          const index_exprt index{
            expr,
            from_integer(new_offset / sub_width, array_type.index_type())};
          op.push_back(bv_get_rec(index, bv, offset + new_offset));
        }
 
        exprt dest=exprt(ID_array, type);
        dest.operands().swap(op);
        return dest;
      }
      else
      {
        return array_exprt{{}, array_type};
      }
    }
    else if(type.id() == ID_struct || type.id() == ID_struct_tag)
    {
      const struct_typet::componentst &components =
        type.id() == ID_struct
          ? to_struct_type(type).components()
          : ns.follow_tag(to_struct_tag_type(type)).components();
      std::size_t new_offset=0;
      exprt::operandst op;
      op.reserve(components.size());
 
      for(const auto &c : components)
      {
        const typet &subtype = c.type();
 
        const member_exprt member{expr, c.get_name(), subtype};
        op.push_back(bv_get_rec(member, bv, offset + new_offset));
 
        new_offset += boolbv_width(subtype);
      }
 
      return struct_exprt(std::move(op), type);
    }
    else if(type.id() == ID_union || type.id() == ID_union_tag)
    {
      const union_typet::componentst &components =
        type.id() == ID_union
          ? to_union_type(type).components()
          : ns.follow_tag(to_union_tag_type(type)).components();
 
      if(components.empty())
        return empty_union_exprt(type);
 
      // Any idea that's better than just returning the first component?
      std::size_t component_nr=0;
 
      const typet &subtype = components[component_nr].type();
 
      const member_exprt member{
        expr, components[component_nr].get_name(), subtype};
      return union_exprt(
        components[component_nr].get_name(),
        bv_get_rec(member, bv, offset),
        type);
    }
    else if(type.id()==ID_complex)
    {
      const std::size_t width = boolbv_width(type);
 
      const typet &subtype = to_complex_type(type).subtype();
      const std::size_t sub_width = boolbv_width(subtype);
      CHECK_RETURN(sub_width > 0);
      DATA_INVARIANT(
        width == sub_width * 2,
        "complex type has two elements of equal bit width");
 
      return complex_exprt{
        bv_get_rec(complex_real_exprt{expr}, bv, 0 * sub_width),
        bv_get_rec(complex_imag_exprt{expr}, bv, 1 * sub_width),
        to_complex_type(type)};
    }
  }
 
  const std::size_t width = boolbv_width(type);
  PRECONDITION(bv.size() >= offset + width);
 
  std::string value;
  value.reserve(width);
 
  for(std::size_t bit_nr=offset; bit_nr<offset+width; bit_nr++)
  {
    char ch = '0';
    // clang-format off
    switch(prop.l_get(bv[bit_nr]).get_value())
    {
    case tvt::tv_enumt::TV_FALSE: ch = '0'; break;
    case tvt::tv_enumt::TV_TRUE: ch = '1'; break;
    case tvt::tv_enumt::TV_UNKNOWN: ch = '0'; break;
    }
    // clang-format on
 
    value += ch;
  }
 
  // The above collects bits starting with the least significant bit,
  // but we need the most significant bit first.
  std::reverse(value.begin(), value.end());
 
  switch(bvtype)
  {
  case bvtypet::IS_UNKNOWN:
    PRECONDITION(type.id() == ID_string || type.id() == ID_empty);
    if(type.id()==ID_string)
    {
      mp_integer int_value=binary2integer(value, false);
      irep_idt s;
      if(int_value>=string_numbering.size())
        s=irep_idt();
      else
        s = string_numbering[numeric_cast_v<std::size_t>(int_value)];
 
      return constant_exprt(s, type);
    }
    else if(type.id() == ID_empty)
    {
      return constant_exprt{irep_idt(), type};
    }
    break;
 
  case bvtypet::IS_RANGE:
  {
    mp_integer int_value = binary2integer(value, false);
    mp_integer from = string2integer(type.get_string(ID_from));
 
    return constant_exprt(integer2string(int_value + from), type);
    break;
  }
 
  case bvtypet::IS_C_BIT_FIELD:
  case bvtypet::IS_VERILOG_UNSIGNED:
  case bvtypet::IS_VERILOG_SIGNED:
  case bvtypet::IS_C_BOOL:
  case bvtypet::IS_FIXED:
  case bvtypet::IS_FLOAT:
  case bvtypet::IS_UNSIGNED:
  case bvtypet::IS_SIGNED:
  case bvtypet::IS_BV:
  case bvtypet::IS_C_ENUM:
  {
    const irep_idt bvrep = make_bvrep(
      width, [&value](size_t i) { return value[value.size() - i - 1] == '1'; });
    return constant_exprt(bvrep, type);
  }
  }
 
  UNREACHABLE;
}
 
exprt boolbvt::bv_get(const bvt &bv, const typet &type) const
{
  nil_exprt skeleton;
  skeleton.type() = type;
  return bv_get_rec(skeleton, bv, 0);
}
 
exprt boolbvt::bv_get_cache(const exprt &expr) const
{
  if(expr.is_boolean())
    return get(expr);
 
  // look up literals in cache
  bv_cachet::const_iterator it=bv_cache.find(expr);
  CHECK_RETURN(it != bv_cache.end());
 
  return bv_get(it->second, expr.type());
}
 
exprt boolbvt::bv_get_unbounded_array(const exprt &expr) const
{
  // first, try to get size
 
  const typet &type=expr.type();
  const exprt &size_expr=to_array_type(type).size();
  exprt size=simplify_expr(get(size_expr), ns);
 
  // get the numeric value, unless it's infinity
  const auto size_opt = numeric_cast<mp_integer>(size);
 
  // search array indices, and only use those applicable to a particular model
  // (array theory may have seen other indices, which might only be live under a
  // different model)
 
  typedef std::map<mp_integer, exprt> valuest;
  valuest values;
 
  const auto opt_num = arrays.get_number(expr);
  if(opt_num.has_value())
  {
    // get root
    const auto number = arrays.find_number(*opt_num);
 
    CHECK_RETURN(number < index_map.size());
    index_mapt::const_iterator it=index_map.find(number);
    CHECK_RETURN(it != index_map.end());
    const index_sett &index_set=it->second;
 
    for(index_sett::const_iterator it1=
        index_set.begin();
        it1!=index_set.end();
        it1++)
    {
      index_exprt index(expr, *it1);
 
      exprt value=bv_get_cache(index);
      exprt index_value=bv_get_cache(*it1);
 
      if(!index_value.is_nil())
      {
        const auto index_mpint = numeric_cast<mp_integer>(index_value);
 
        if(
          index_mpint.has_value() && *index_mpint >= 0 &&
          (!size_opt.has_value() || *index_mpint < *size_opt))
        {
          if(value.is_nil())
            values[*index_mpint] =
              exprt(ID_unknown, to_array_type(type).element_type());
          else
            values[*index_mpint] = value;
        }
      }
    }
  }
 
  exprt result;
 
  if(!size_opt.has_value() || values.size() != *size_opt)
  {
    result = array_list_exprt({}, to_array_type(type));
 
    result.operands().reserve(values.size()*2);
 
    for(valuest::const_iterator it=values.begin();
        it!=values.end();
        it++)
    {
      exprt index=from_integer(it->first, size.type());
      result.add_to_operands(std::move(index), exprt{it->second});
    }
  }
  else
  {
    // set the size
    result=exprt(ID_array, type);
 
    // allocate operands
    std::size_t size_int = numeric_cast_v<std::size_t>(*size_opt);
    result.operands().resize(size_int, exprt{ID_unknown});
 
    // search uninterpreted functions
 
    for(valuest::iterator it=values.begin();
        it!=values.end();
        it++)
    {
      result.operands()[numeric_cast_v<std::size_t>(it->first)].swap(
        it->second);
    }
  }
 
  return result;
}
 
mp_integer boolbvt::get_value(
  const bvt &bv,
  std::size_t offset,
  std::size_t width)
{
  PRECONDITION(offset + width <= bv.size());
 
  mp_integer value=0;
  mp_integer weight=1;
 
  for(std::size_t bit_nr=offset; bit_nr<offset+width; bit_nr++)
  {
    switch(prop.l_get(bv[bit_nr]).get_value())
    {
     case tvt::tv_enumt::TV_FALSE:   break;
     case tvt::tv_enumt::TV_TRUE:    value+=weight; break;
     case tvt::tv_enumt::TV_UNKNOWN: break;
     default:
       UNREACHABLE;
    }
 
    weight*=2;
  }
 
  return value;
}