Remove most significant bit

To remove the most significant bit of a number x with its bit size k, we could apply

x &= (1 << (k-1))-1;

e.g. x = 0b11111111, k = 8

(1 << (8-1)) = 0b10000000
(1 << (8-1))-1 = 0b01111111

0b11111111 & (1 << (8-1))-1
= 0b11111111 & 0b01111111
= 0b01111111 (most significant bit removed!)