Does the Kotlin standard library offer a version o...

# getting-started

[Kelvin Chung]

Does the Kotlin standard library offer a version of the modulus/remainder function that guarantees a non-negative result? I only see a version that preserves the sign of the left operand and a version that preserves the sign of the right operand.

[AndreyVanDenHaag]

I do my best to understand your question, but I fail. Any code snippet to show your expectation?

[Stephan Schröder]

I think what @Kelvin Chung is taling about is that -5%2 evaluates to -1 and not 1 .

[Stephan Schröder]

In which case the mod function is your friend: (-5).mod(2) -> 1

[Klitos Kyriacou]

@Stephan Schröder I don't think so, since "I only see a version that preserves the sign of the left operand" is rem (%) and "a version that preserves the sign of the right operand" is mod. Neither rem nor mod meets the stated requirement that it "guarantees a non-negative result". Having said that, I cannot think of any valid use case for such a requirement.

[Stephan Schröder]

@Klitos Kyriacou I can't even think about a usecase where the right operand is negative, that being said, I think this would be the extension function to have the desired behaviour:

fun Int.posRemainder(other:Int): Int = (this%other).let { rem->
    if(rem>=0) {
        rem
    } else {
        rem + kotlin.math.abs(other)
    }
}

[Gleb Minaev]

Why not

fun Int.posRemainder(other:Int): Int = this.mod(abs(other))

then?

[Kelvin Chung]

For the record, Java's BigInteger has it that rem acts like % (preserves the sign of the left operand) and mod guarantees a non-negative result; they don't have an operation that preserves the sign of the right operand. Which is very confusing.

[Klitos Kyriacou]

@Kelvin Chung It does preserve the sign of the right operand, but the right operand must be positive, and therefore the result also happens to be always positive.