Add xorwow random implementation test and fix implementation

libraries/stdlib/test/random/XorWowRandomImplTest.kt

@@ -0,0 +1,27 @@
+/*
+ * 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 test.random
+
+import kotlin.math.pow
+import kotlin.random.*
+import kotlin.test.*
+
+class XorWowRandomImplTest {
+    @Test
+    fun predefinedSequence() {
+        val seed = 1
+        val addend = (seed shl 10) xor (seed ushr 4)
+
+        @Suppress("INVISIBLE_REFERENCE", "INVISIBLE_MEMBER")
+        val random: Random = XorWowRandom(seed, 0, 0, 0, 0, addend)
+
+        // differs from reference 0.8178000247146859 because of different double mixing algorithm
+        assertEquals(0.817799582443095, random.nextDouble())
+
+        assertEquals(0.8407576507888734, random.nextBits(31) / (2.0.pow(31)))
+        assertEquals(533150816, random.nextInt())
+    }
+}