Round decimal to n significant places

significant_round.kt

infix fun Double.roundToSig(places: Int): Double {
    val order = log10(this).roundToInt() + 1

    val shift = 10.0.pow(places - order)

    return round(this * shift) / shift
}

fun testRoundToSig() {
    assert(12.9.roundToSig(2).toString() == "13.0")
    assert(12.9.roundToSig(3).toString() == "12.9")
    assert(123.9.roundToSig(2).toString() == "120.0")
    assert(123.9.roundToSig(3).toString() == "124.0")
    assert(0.0129.roundToSig(2).toString() == "0.013")
    assert(0.0129.roundToSig(3).toString() == "0.0129")
    assert(0.01239.roundToSig(2).toString() == "0.012")
    assert(0.01239.roundToSig(3).toString() == "0.0124")
    assert(19.9.roundToSig(2).toString() == "20.0")
    assert(0.0199.roundToSig(2).toString() == "0.02")
}