Reputation: 52163

Round Half Down in Swift

Is there a rounding mode in Swift that behaves same as ROUND_HALF_DOWN in Java?

Rounding mode to round towards "nearest neighbor" unless both neighbors are equidistant, in which case round down. Behaves as for RoundingMode.UP if the discarded fraction is > 0.5; otherwise, behaves as for RoundingMode.DOWN.

Example:

2.5 rounds down to 2.0
2.6 rounds up to 3.0
2.4 rounds down to 2.0

For a negative number:

-2.5 rounds up to -2.0
-2.6 rounds down to -3.0
-2.4 rounds up to -2.0

Upvotes: 2

Answers (5)

Martin R

Reputation: 539815

There is – as far as I can tell – no FloatingPointRoundingRule with the same behavior as Java's ROUND_HALF_DOWN, but you can get the result with a combination of rounded() and nextDown or nextUp:

func roundHalfDown(_ x: Double) -> Double {
    if x >= 0 {
        return x.nextDown.rounded()
    } else {
        return x.nextUp.rounded()
    }
}

Examples:

print(roundHalfDown(2.4)) // 2.0
print(roundHalfDown(2.5)) // 2.0
print(roundHalfDown(2.6)) // 3.0

print(roundHalfDown(-2.4)) // -2.0
print(roundHalfDown(-2.5)) // -2.0
print(roundHalfDown(-2.6)) // -3.0

Or as a generic extension method, so that it can be used with all floating point types (Float, Double, CGFloat):

extension FloatingPoint {
    func roundedHalfDown() -> Self {
        return self >= 0 ? nextDown.rounded() : nextUp.rounded()
    }
}

Examples:

print((2.4).roundedHalfDown()) // 2.0
print((2.5).roundedHalfDown()) // 2.0
print((2.6).roundedHalfDown()) // 3.0

print((-2.4).roundedHalfDown()) // -2.0
print((-2.5).roundedHalfDown()) // -2.0
print((-2.6).roundedHalfDown()) // -3.0

Upvotes: 5

Arash Etemad

Reputation: 1909

As @MohmmadS said those are built in methods for rounding.

You can implement custom rounding like this:

func round(_ value: Double, toNearest: Double) -> Double {
    return round(value / toNearest) * toNearest
}

func roundDown(_ value: Double, toNearest: Double) -> Double {
    return floor(value / toNearest) * toNearest
}

func roundUp(_ value: Double, toNearest: Double) -> Double {
    return ceil(value / toNearest) * toNearest
}

Example:

round(52.376, toNearest: 0.01) // 52.38
round(52.376, toNearest: 0.1)  // 52.4
round(52.376, toNearest: 0.25) // 52.5
round(52.376, toNearest: 0.5)  // 52.5
round(52.376, toNearest: 1)    // 52

Upvotes: 0

Deviyani Swami

Reputation: 767

 var a = 6.54
        a.round(.toNearestOrAwayFromZero)
        // a == 7.0

        var b = 6.54
        b.round(.towardZero)
        // b == 6.0


        var c = 6.54
        c.round(.up)
        // c == 7.0


        var d = 6.54
        d.round(.down)
        // d == 6.0

You can do like this as well but need to take values after decimal as well.

Upvotes: 0