Constant sunrise_kernel::frame_allocator::i386::FRAME_BASE_MASK

const FRAME_BASE_MASK: usize = !FRAME_OFFSET_MASK; // 18_446_744_073_709_547_520usize

The frame part in PhysicalAddress.

let phys_address = PhysicalAddress(0xccccc567);

let frame_addr = phys_address & FRAME_BASE_MASK;
assert_eq!(offset_in_frame, 0xccccc000);