ptable_size
#define ptable_mask(type) ((1U << (PAGE_SIZE / ptable_size(type))) - 1)
unsigned int mask = 1U << ((ptable - pt_addr)/ptable_size(type));
for (tmp = 1, off = 0; (mask & tmp) == 0; tmp <<= 1, off += ptable_size(type))
unsigned int mask = 1U << ((ptable - pt_addr)/ptable_size(type));