fixmul (3) - Linux Manuals

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

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.