Provide common Random API

#KT-17261

libraries/stdlib/jvm/src/kotlin/internal/PlatformImplementations.kt

@@ -7,6 +7,8 @@ package kotlin.internal
 
 import kotlin.*
 import java.util.regex.MatchResult
+import kotlin.random.FallbackThreadLocalRandom
+import kotlin.random.Random
 
 internal open class PlatformImplementations {
 
@@ -17,6 +19,8 @@ internal open class PlatformImplementations {
     public open fun getMatchResultNamedGroup(matchResult: MatchResult, name: String): MatchGroup? {
         throw UnsupportedOperationException("Retrieving groups by name is not supported on this platform.")
     }
+
+    public open fun defaultPlatformRandom(): Random = FallbackThreadLocalRandom()
 }
 
 

libraries/stdlib/jvm/src/kotlin/random/PlatformRandom.kt

@@ -0,0 +1,73 @@
+/*
+ * Copyright 2010-2018 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.
+ */
+
+package kotlin.random
+
+import kotlin.UnsupportedOperationException
+import kotlin.internal.*
+
+@SinceKotlin("1.3")
+public fun Random.asJavaRandom(): java.util.Random =
+    (this as? AbstractPlatformRandom)?.impl ?: KotlinRandom(this)
+
+@SinceKotlin("1.3")
+public fun java.util.Random.asKotlinRandom(): Random =
+    PlatformRandom(this)
+
+
+
+@InlineOnly
+internal actual inline fun defaultPlatformRandom(): Random =
+    IMPLEMENTATIONS.defaultPlatformRandom()
+
+internal actual fun fastLog2(value: Int): Int =
+    31 - Integer.numberOfLeadingZeros(value)
+
+
+internal abstract class AbstractPlatformRandom : Random() {
+    abstract val impl: java.util.Random
+
+    override fun nextBits(bitCount: Int): Int = impl.nextInt() ushr (32 - bitCount).coerceAtLeast(0)
+
+    override fun nextInt(): Int = impl.nextInt()
+    override fun nextLong(): Long = impl.nextLong()
+    override fun nextBoolean(): Boolean = impl.nextBoolean()
+    override fun nextDouble(): Double = impl.nextDouble()
+    override fun nextFloat(): Float = impl.nextFloat()
+
+    override fun nextBytes(array: ByteArray): ByteArray = run { impl.nextBytes(array); array }
+}
+
+internal class FallbackThreadLocalRandom : AbstractPlatformRandom() {
+    private val implStorage = object : ThreadLocal<java.util.Random>() {
+        override fun initialValue(): java.util.Random {
+            return java.util.Random()
+        }
+    }
+    override val impl: java.util.Random
+        get() = implStorage.get()
+}
+
+private class PlatformRandom(override val impl: java.util.Random) : AbstractPlatformRandom()
+
+private class KotlinRandom(val impl: Random) : java.util.Random() {
+    override fun next(bits: Int): Int = impl.nextBits(bits)
+    override fun nextInt(): Int = impl.nextInt()
+    override fun nextInt(bound: Int): Int = impl.nextInt(bound)
+    override fun nextBoolean(): Boolean = impl.nextBoolean()
+    override fun nextLong(): Long = impl.nextLong()
+    override fun nextFloat(): Float = impl.nextFloat()
+    override fun nextDouble(): Double = impl.nextDouble()
+
+    override fun setSeed(seed: Long) {
+        throw UnsupportedOperationException("Setting seed is not supported")
+    }
+
+    override fun nextBytes(bytes: ByteArray) {
+        impl.nextBytes(bytes)
+    }
+}
+
+