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fixsub(3)                       Allegro manual                       fixsub(3)

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

Allegro                          version 4.4.2                       fixsub(3)