XOR (exclusive or) is one of my favorite logical operations! XOR stands for exclusive or since it's a variant of the logical OR operation. XOR takes two operands and returns 1 if and only if exactly one operand is 1.

You can experiment with XOR with this online XOR calculator.

When the operands contain multiple bits, XOR is performed bitwise, meaning the first bit of x is XOR'd with the first bit of y, then the second bits XOR'd with each other, and so on.

This can be used to alternate some numeric variable between two values! The easiest example is using a single bit to alternate between 0 and 1:

mask = 1;

1 XOR mask = 0

0 XOR mask = 1

But what if you want to alternate between other values, like 17 and 5? Whatever your operands are, the mask is equal to x XOR y! Wow!

mask = 17 XOR 5 = 12

17 XOR mask = 5

5 XOR mask = 17

Okay, the practical applications might be limited at first glance. I still love this trick, especially as an aspiring low-level programmer. Check out this cool Fibonacci sequence generator I wrote in Rust:

// Returns the nth element in the Fibonacci sequence.
fn nth_fib(n: usize) -> u128 {
    let mut work: [u128; 2] = [0, 1];

    let mut idx: usize = 0;

    for _ in 2..=n {
        work[0]
            .checked_add(work[1]) // Return `None` if an overflow occurs.
            .map_or_else(|| panic!("Overflowed!"), |n| work[idx] = n);

        // Alternate between 0 and 1
        idx ^= 0x1;
    }

    work[idx]
}