overflow.go

func checkOverflow(result, op1, op2 uint8) bool {
    // (op1 ^ op2) & 0x80: zero if both operands had the same sign bit
    // (op1 ^ result) & 0x80: non-zero if the result is a different sign
    //                        from the operands
    // So it returns true if either:
    //    both operands are positive but the result is negative
    //    or vice-versa
    return (((op1 ^ op2) & 0x80) == 0) && (((op1 ^ result) & 0x80) != 0)
}