fixsub - Safe function to subtract fixed point numbers clamping underflow. Allegro game programming

       Although fixed point numbers can be subtracted 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 `errno' and clamp the result,
       rather than just letting it wrap. Example:

          fixed result;
          /* This will put 4965 into `result'. */
          result = fixsub(itofix(5000), itofix(35));
          /* Sets `errno' and puts -32768 into `result'. */
          result = fixsub(itofix(-31000), itofix(3000));
          ASSERT(!errno); /* This will fail. */

       fixsub  -  Safe  function  to  subtract  fixed point numbers clamping underflow. Allegro game programming
       library.

       Returns the clamped result of subtracting `y' from `x',  setting  `errno'  to  ERANGE  if  there  was  an
       overflow.

fixadd(3alleg4), fixmul(3alleg4), fixdiv(3alleg4)

Allegro                                           version 4.4.3                                  fixsub(3alleg4)

#include<allegro.h>fixedfixsub(fixedx,fixedy);