al_fixmul - Allegro 5 API
#include <allegro5/allegro.h> al_fixed al_fixmul(al_fixed x, al_fixed y);
A fixed point value can be multiplied or divided by an integer with the normal * and / operators. To multiply two fixed point values, though, you must use this function.
If an overflow occurs, Allegro’s errno will be set and the maximum possible value will be returned, but errno is not cleared if the operation is successful. This means that if you are going to test for overflow you should call al_set_errno(0) before calling al_fixmul(3).
al_fixed result; /* This will put 30000 into `result'. */ result = al_fixmul(al_itofix(10), al_itofix(3000)); /* But this overflows, and sets errno. */ result = al_fixmul(al_itofix(100), al_itofix(3000)); assert(!al_get_errno());
Returns the clamped result of multiplying x by y, setting Allegro’s errno to ERANGE if there was an overflow.
al_fixadd(3), al_fixsub(3), al_fixdiv(3), al_get_errno(3).
|Allegro reference manual|