suse man page for fixmul

fixmul(3alleg4)                                                   Allegro manual                                                   fixmul(3alleg4)

NAME
       fixmul - Multiplies two fixed point values together. Allegro game programming library.

SYNOPSIS
       #include <allegro.h>

       fixed fixmul(fixed x, fixed y);

DESCRIPTION
       A  fixed  point value can be multiplied or divided by an integer with the normal `*' and `/' operators. To multiply two fixed point values,
       though, you must use this function.

       If an overflow occurs, `errno' will be set and the maximum possible value will be returned, but `errno' is not cleared if the operation  is
       successful. This means that if you are going to test for overflow you should set `errno=0' before calling fixmul(). Example:

          fixed result;

          /* This will put 30000 into `result'. */
          result = fixmul(itofix(10), itofix(3000));
          /* But this overflows, and sets `errno'. */
          result = fixmul(itofix(100), itofix(3000));
          ASSERT(!errno);

RETURN VALUE
       Returns the clamped result of multiplying `x' by `y', setting `errno' to ERANGE if there was an overflow.

SEE ALSO
       fixadd(3alleg4),   fixsub(3alleg4),   fixdiv(3alleg4),   ex3buf(3alleg4),   excustom(3alleg4),  exfixed(3alleg4),  exspline(3alleg4),  exs-
       tars(3alleg4), exupdate(3alleg4)

Allegro                                                            version 4.4.2                                                   fixmul(3alleg4)