boolbv_case.cpp

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/*******************************************************************\
 
Module:
 
Author: Daniel Kroening, kroening@kroening.com
 
\*******************************************************************/
 
#include "boolbv.h"
 
#include <util/invariant.h>
 
bvt boolbvt::convert_case(const exprt &expr)
{
  PRECONDITION(expr.id() == ID_case);
 
  const std::vector<exprt> &operands=expr.operands();
 
  std::size_t width=boolbv_width(expr.type());
 
  // make it free variables
  bvt bv = prop.new_variables(width);
 
  DATA_INVARIANT(
    operands.size() >= 3, "case should have at least three operands");
 
  DATA_INVARIANT(
    operands.size() % 2 == 1, "number of case operands should be odd");
 
  enum { FIRST, COMPARE, VALUE } what=FIRST;
  bvt compare_bv;
  literalt previous_compare=const_literal(false);
  literalt compare_literal=const_literal(false);
 
  for(const auto &operand : expr.operands())
  {
    bvt op = convert_bv(operand);
 
    switch(what)
    {
    case FIRST:
      compare_bv.swap(op);
      what=COMPARE;
      break;
 
    case COMPARE:
      DATA_INVARIANT(
        compare_bv.size() == op.size(),
        std::string("size of compare operand does not match:\n") +
          "compare operand: " + std::to_string(compare_bv.size()) +
          "\noperand: " + std::to_string(op.size()) + '\n' + operand.pretty());
 
      compare_literal=bv_utils.equal(compare_bv, op);
      compare_literal=prop.land(!previous_compare, compare_literal);
 
      previous_compare=prop.lor(previous_compare, compare_literal);
 
      what=VALUE;
      break;
 
    case VALUE:
      DATA_INVARIANT(
        bv.size() == op.size(),
        std::string("size of value operand does not match:\n") +
          "result size: " + std::to_string(bv.size()) +
          "\noperand: " + std::to_string(op.size()) + '\n' + operand.pretty());
 
      {
        literalt value_literal=bv_utils.equal(bv, op);
 
        prop.l_set_to_true(
          prop.limplies(compare_literal, value_literal));
      }
 
      what=COMPARE;
      break;
 
    default:
      UNREACHABLE;
    }
  }
 
  return bv;
}