al_fixadd - Allegro 5 API

       Although  fixed  point  numbers can be added with the normal + integer operator, that doesn’t provide any
       protection against overflow.  If overflow is a problem, you should use  this  function  instead.   It  is
       slower  than using integer operators, but if an overflow occurs it will set Allegro’s errno and clamp the
       result, rather than just letting it wrap.

       Example:

              al_fixed result;

              /* This will put 5035 into `result'. */
              result = al_fixadd(al_itofix(5000), al_itofix(35));

              /* Sets errno and puts -32768 into `result'. */
              result = al_fixadd(al_itofix(-31000), al_itofix(-3000));
              assert(!al_get_errno()); /* This will fail. */

       al_fixadd - Allegro 5 API

       Returns the clamped result of adding x to y, setting Allegro’s errno to ERANGE if there was an overflow.

al_fixsub(3alleg5), al_fixmul(3alleg5), al_fixdiv(3alleg5).

Allegro reference manual                                                                      al_fixadd(3alleg5)

              #include <allegro5/allegro.h>

              al_fixed al_fixadd(al_fixed x, al_fixed y);