boolbv_update.cpp

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/*******************************************************************\
 
Module:
 
Author: Daniel Kroening, kroening@kroening.com
 
\*******************************************************************/
 
#include "boolbv.h"
 
#include <util/arith_tools.h>
#include <util/c_types.h>
#include <util/namespace.h>
 
bvt boolbvt::convert_update(const update_exprt &expr)
{
  const exprt::operandst &ops=expr.operands();
 
  std::size_t width=boolbv_width(expr.type());
 
  bvt bv=convert_bv(ops[0]);
 
  if(bv.size()!=width)
    throw "update: unexpected operand 0 width";
 
  // start the recursion
  convert_update_rec(
    expr.op1().operands(), 0, expr.type(), 0, expr.op2(), bv);
 
  return bv;
}
 
void boolbvt::convert_update_rec(
  const exprt::operandst &designators,
  std::size_t d,
  const typet &type,
  std::size_t offset,
  const exprt &new_value,
  bvt &bv)
{
  if(d>=designators.size())
  {
    // done
    bvt new_value_bv=convert_bv(new_value);
    std::size_t new_value_width=boolbv_width(type);
 
    if(new_value_width!=new_value_bv.size())
      throw "convert_update_rec: unexpected new_value size";
 
    // update
    for(std::size_t i=0; i<new_value_width; i++)
    {
      DATA_INVARIANT(offset + i < bv.size(), "update must be in bounds");
      bv[offset+i]=new_value_bv[i];
    }
 
    return;
  }
 
  const exprt &designator=designators[d];
 
  if(designator.id()==ID_index_designator)
  {
    if(type.id()!=ID_array)
      throw "update: index designator needs array";
 
    if(designator.operands().size()!=1)
      throw "update: index designator takes one operand";
 
    bvt index_bv = convert_bv(to_index_designator(designator).index());
 
    const array_typet &array_type=to_array_type(type);
    const typet &subtype = array_type.element_type();
    const exprt &size_expr = array_type.size();
 
    std::size_t element_size=boolbv_width(subtype);
 
    DATA_INVARIANT(
      size_expr.is_constant(),
      "array in update expression should be constant-sized");
 
    // iterate over array
    const std::size_t size =
      numeric_cast_v<std::size_t>(to_constant_expr(size_expr));
 
    bvt tmp_bv=bv;
 
    for(std::size_t i = 0; i != size; ++i)
    {
      std::size_t new_offset=offset+i*element_size;
 
      convert_update_rec(
        designators, d+1, subtype, new_offset, new_value, tmp_bv);
 
      bvt const_bv=bv_utils.build_constant(i, index_bv.size());
      literalt equal=bv_utils.equal(const_bv, index_bv);
 
      for(std::size_t j=0; j<element_size; j++)
      {
        std::size_t idx=new_offset+j;
        DATA_INVARIANT(idx < bv.size(), "index must be in bounds");
        bv[idx]=prop.lselect(equal, tmp_bv[idx], bv[idx]);
      }
    }
  }
  else if(designator.id()==ID_member_designator)
  {
    const irep_idt &component_name=designator.get(ID_component_name);
 
    if(type.id() == ID_struct || type.id() == ID_struct_tag)
    {
      const struct_typet &struct_type =
        type.id() == ID_struct_tag ? ns.follow_tag(to_struct_tag_type(type))
                                   : to_struct_type(type);
 
      std::size_t struct_offset=0;
 
      struct_typet::componentt component;
      component.make_nil();
 
      const struct_typet::componentst &components=
        struct_type.components();
 
      for(const auto &c : components)
      {
        const typet &subtype = c.type();
        std::size_t sub_width=boolbv_width(subtype);
 
        if(c.get_name() == component_name)
        {
          component = c;
          break; // done
        }
 
        struct_offset+=sub_width;
      }
 
      if(component.is_nil())
        throw "update: failed to find struct component";
 
      const typet &new_type = component.type();
 
      std::size_t new_offset=offset+struct_offset;
 
      // recursive call
      convert_update_rec(
        designators, d+1, new_type, new_offset, new_value, bv);
    }
    else if(type.id() == ID_union || type.id() == ID_union_tag)
    {
      const union_typet &union_type = type.id() == ID_union_tag
                                        ? ns.follow_tag(to_union_tag_type(type))
                                        : to_union_type(type);
 
      const union_typet::componentt &component=
        union_type.get_component(component_name);
 
      if(component.is_nil())
        throw "update: failed to find union component";
 
      // this only adjusts the type, the offset stays as-is
 
      const typet &new_type = component.type();
 
      // recursive call
      convert_update_rec(
        designators, d+1, new_type, offset, new_value, bv);
    }
    else
      throw "update: member designator needs struct or union";
  }
  else
    throw "update: unexpected designator";
}