al_fixacos - Allegro 5 API

       This  function finds the inverse cosine of a value using a lookup table.  The input must be a fixed point
       value.  The inverse cosine is defined only in the domain from -1 to 1.  Outside of this input range,  the
       function will set Allegro’s errno to EDOM and return zero.

       Example:

              al_fixed result;

              /* Sets result to binary angle 128. */
              result = al_fixacos(al_itofix(-1));

       al_fixacos - Allegro 5 API

       Returns  the inverse sine of a fixed point value, measured as fixed point binary format angle, or zero if
       the input was out of range.  All return values of this function will be in the range 0 to 128.

Allegro reference manual                                                                     al_fixacos(3alleg5)

              #include <allegro5/allegro.h>

              al_fixed al_fixacos(al_fixed x);