man fixsub () - Safe function to subtract fixed point numbers clamping underflow. Allegro game programming library.
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(5), itofix(3)); /* Sets `errno' and puts -32768 into `result'. */ result = fixsub(itofix(-31000), itofix(3)); 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.