Function alcibiades::bitsets::below_lsb_including

pub fn below_lsb_including(x: Bitboard) -> Bitboard

Returns a mask with all bits below and including the LSB set to 1.

The way to calculate this is: below_lsb_including = x ^ (x - 1);.

If x is 0 this function returns 0xffffffffffffffff.

Examples:

assert_eq!(below_lsb_including(0b10100), 0b111);
assert_eq!(below_lsb_including(0), !0);

      x          ^      (x - 1)      =  below_lsb_including(x)
. . . . . . . .     . . . . . . . .     . . . . . . . .
. . 1 . 1 . . .     . . 1 . 1 . . .     . . . . . . . .
. 1 . . . 1 . .     . 1 . . . 1 . .     . . . . . . . .
. . . . . . . .     . . . . . . . .     . . . . . . . .
. 1 . . . 1 . .  ^  . 1 . . . 1 . .  =  . . . . . . . .
. . 1 . 1 . . .     1 1 . . 1 . . .     1 1 1 . . . . .
. . . . . . . .     1 1 1 1 1 1 1 1     1 1 1 1 1 1 1 1
. . . . . . . .     1 1 1 1 1 1 1 1     1 1 1 1 1 1 1 1