Initial prototype of Duration and Clocks API

libraries/stdlib/jvm/src/kotlin/time/DurationUnitJvm.kt

@@ -0,0 +1,26 @@
+/*
+ * Copyright 2010-2019 JetBrains s.r.o. Use of this source code is governed by the Apache 2.0 license
+ * that can be found in the license/LICENSE.txt file.
+ */
+
+@file:kotlin.jvm.JvmMultifileClass()
+@file:kotlin.jvm.JvmName("DurationUnitKt")
+
+package kotlin.time
+
+//Actual typealias 'DurationUnit' has no corresponding expected declaration
+//The following declaration is incompatible because modality is different:
+//    public final expect enum class DurationUnit : Enum<DurationUnit>
+
+@Suppress("ACTUAL_WITHOUT_EXPECT")
+public actual typealias DurationUnit = java.util.concurrent.TimeUnit
+
+
+public actual fun convertDurationUnit(value: Double, sourceUnit: DurationUnit, targetUnit: DurationUnit): Double {
+    val sourceInTargets = targetUnit.convert(1, sourceUnit)
+    if (sourceInTargets > 0)
+        return value * sourceInTargets
+
+    val otherInThis = sourceUnit.convert(1, targetUnit)
+    return value / otherInThis
+}

libraries/stdlib/jvm/src/kotlin/time/MonoClock.kt

@@ -0,0 +1,12 @@
+/*
+ * Copyright 2010-2019 JetBrains s.r.o. and Kotlin Programming Language contributors.
+ * Use of this source code is governed by the Apache 2.0 license that can be found in the license/LICENSE.txt file.
+ */
+
+package kotlin.time
+
+public actual object MonoClock : LongReadingClock(), Clock { // TODO: interface should not be required here
+    override fun reading(): Long = System.nanoTime()
+    override fun toString(): String = "Clock(System.nanoTime())"
+    override val unit: DurationUnit = DurationUnit.NANOSECONDS
+}

libraries/stdlib/jvm/src/kotlin/time/formatToDecimals.kt

@@ -0,0 +1,11 @@
+/*
+ * Copyright 2010-2019 JetBrains s.r.o. and Kotlin Programming Language contributors.
+ * Use of this source code is governed by the Apache 2.0 license that can be found in the license/LICENSE.txt file.
+ */
+
+package kotlin.time
+
+import java.util.*
+
+internal actual fun formatToDecimals(value: Double, decimals: Int, unitName: String): String =
+    String.format(Locale.ROOT, "%.${decimals}f%s", value, unitName)