code: def eval(self, expr, n, extra_constraints=(), solver=None, model_callback=None):
          
          if self._solver_required and solver is None:
              raise BackendError("%s requires a solver for evaluation" % self.__class__.__name__)
  
          results = self._eval(
              self.convert(expr), n, extra_constraints=self.convert_list(extra_constraints),
              solver=solver, model_callback=model_callback
          )
  
          results = list(results)
          if type(expr) is not BV:
              return results
  
          size = expr.length
          for i in range(len(results)):
              results[i] &= (1 << size) - 1 # convert it back to unsigned
  
          # solver is done, terminate process
          solver.terminate()
  
          return results
docs: This function returns up to `n` possible solutions for expression `expr`.
  
          :param expr: expression (an AST) to evaluate
          :param n: number of results to return
          :param solver: a solver object, native to the backend, to assist in
                         the evaluation (for example, a z3.Solver)
          :param extra_constraints: extra constraints (as ASTs) to add to the solver for this solve
          :param model_callback:      a function that will be executed with recovered models (if any)
          :return:              A sequence of up to n results (backend objects)