It is easy to prove we do not need & !0x7 because the maximum value it can operate on is 00001000_00000111_00000110_00000101_00000100_00000011_00000010_00000001 >> 53. Since the byte under the most significant byte can be a 7 at most, the upper 3 bits of that second byte are always 0. Therefore we do not need to zero them out.
00001000_00000111_00000110_00000101_00000100_00000011_00000010_00000001
^^^ these are always 0
It is easy to prove we do not need
& !0x7because the maximum value it can operate on is00001000_00000111_00000110_00000101_00000100_00000011_00000010_00000001 >> 53. Since the byte under the most significant byte can be a 7 at most, the upper 3 bits of that second byte are always 0. Therefore we do not need to zero them out.