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(3alleg), fixmul(3alleg), fixdiv(3alleg)