/**
 * @name Conversion changes sign
 * @description Finds conversions from unsigned to signed.
 * @kind problem
 * @id cpp/conversion-changes-sign
 * @problem.severity warning
 * @tags reliability
 */
import cpp

from Expr e1, Cast e2, IntegralType it1, IntegralType it2
where e2 = e1.getConversion() and
      e2.isImplicit() and
      it1 = e1.getUnderlyingType() and
      it2 = e2.getUnderlyingType() and
      (
        it1.isUnsigned() and it2.isSigned() and it1.getSize() >= it2.getSize()
        or it1.isSigned() and it2.isUnsigned()
      ) and
      not (e1.isConstant() and 0 <= e1.getValue().toInt() and
                         e1.getValue().toInt() <= ((it2.getSize()*8-1)*(2.log())).exp())
      and not e1.isConstant()
select e1, "Conversion between signed and unsigned types "+it1.toString()+" and "+it2.toString()+"."