Negative number modulo in swift

Question

How does modulo of negative numbers work in swift ? When i did (-1 % 3) it is giving -1 but the remainder is 2. What is the catch in it?

Answer 1

An answer inspired by cdeerinck, which sacrifices speed for simplicity, is this:

infix operator %%

extension Int {

    static  func %% (_ left: Int, _ right: Int) -> Int {
       let mod = left % right
       return mod >= 0 ? mod : mod + right
    }

}

I tested it with this little loop in a playground:

for test in [6, 5, 4, 0, -1, -2, -100, -101] {
    print(test, "%% 5", test %% 5)
}