NAME

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

SYNOPSIS

#include <allegro.h>

fixed fixsub(fixed x, fixed y);

DESCRIPTION

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. */

RETURN VALUE

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

SEE ALSO

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