Virtual Memory map

Hello all, i have a short question: How are the bits (in brackets) calculated in the virtual memory map ? for example the first line (=47 bits) Virtual memory map with 4 level page tables: 0000000000000000 - 00007fffffffffff (=47 bits) user space, different per mm hole caused by [47:63] sign extension ffff800000000000 - ffff87ffffffffff (=43 bits) guard hole, reserved for hypervisor Best regards Damian