fixsub (3) - Linux Man Pages
fixsub: Safe function to subtract fixed point numbers clamping underflow. Allegro game programming library.
NAMEfixsub - Safe function to subtract fixed point numbers clamping underflow. Allegro game programming library.
DESCRIPTIONAlthough 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. */