fixsub - Safe function to subtract fixed point numbers clamping underflow. Allegro game programming library.
fixed fixsub(fixed x, fixed y);
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:
/* 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. */
Returns the clamped result of subtracting `y' from `x', setting `errno' to ERANGE if there was an overflow.
fixadd(3alleg4), fixmul(3alleg4), fixdiv(3alleg4)