What is the "&^" operator in golang?

The &^ operator is bit clear (AND NOT): in the expression z = x &^ y, each bit of z is 0 if the corresponding bit of y is 1; otherwise it equals the corresponding bit of x.

From The Go Programming Language

Example:

package main
import "fmt"

func main(){
    var x uint8 = 1
    var y uint8 = 1 << 2

    fmt.Printf("%08b\n", x &^ y);

}  

Result:

00000001

The C equivalent of the Go expression x &^ y is just x & ~y. That is literally "x AND (bitwise NOT of y)".

In the arithmetic operators section of the spec describes &^ as a "bit clear" operation, which gives an idea of what you'd want to use it for. As two separate operations, ~y will convert each one bit to a zero, which will then clear the corresponding bit in x. Each zero bit will be converted to a one, which will preserve the corresponding bit in x.

So if you think of x | y as a way to turn on certain bits of x based on a mask constant y, then x &^ y is doing the opposite and turns those same bits off.