Method - bitwise meaning

[courteous]

can you please explain what this line exactly in the method bitwise is supposed to do?

var sum = fn(xSign ? 1 : 0, ySign ? 1 : 0) !== 0 ? bigInt(-1) : bigInt(0);

thanks

[Yaffle]

sometimes, -2**k should be subtracted from the result to simulate 2s complement representation

[courteous]

thanks