#ifdef __GNUC__
# define roundup(x, y)  (__builtin_constant_p (y) && powerof2 (y)         \
             ? (((x) + (y) - 1) & ~((y) - 1))             \
             : ((((x) + ((y) - 1)) / (y)) * (y)))
#else
# define roundup(x, y)  ((((x) + ((y) - 1)) / (y)) * (y))
#endif