Use common implementation of fastLog2 based on countLeadingZeroBits

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

@@ -11,17 +11,6 @@ internal actual fun defaultPlatformRandom(): Random =
     Random(js("(Math.random() * Math.pow(2, 32)) | 0").unsafeCast<Int>())
 
 
-internal actual fun fastLog2(value: Int): Int {
-    // TODO: not so fast, make faster
-    var v = value
-    var log = -1
-    while (v != 0) {
-        v = v.ushr(1)
-        log++
-    }
-    return log
-}
-
 private val INV_2_26: Double = 2.0.pow(-26)
 private val INV_2_53: Double = 2.0.pow(-53)
 internal actual fun doubleFromParts(hi26: Int, low27: Int): Double =

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

@@ -28,9 +28,6 @@ public fun java.util.Random.asKotlinRandom(): Random =
 internal actual inline fun defaultPlatformRandom(): Random =
     IMPLEMENTATIONS.defaultPlatformRandom()
 
-internal actual fun fastLog2(value: Int): Int =
-    31 - Integer.numberOfLeadingZeros(value)
-
 internal actual fun doubleFromParts(hi26: Int, low27: Int): Double =
     (hi26.toLong().shl(27) + low27) / (1L shl 53).toDouble()
 

libraries/stdlib/src/kotlin/random/Random.kt

@@ -336,9 +336,11 @@ public fun Random.nextLong(range: LongRange): Long = when {
 
 
 internal expect fun defaultPlatformRandom(): Random
-internal expect fun fastLog2(value: Int): Int //  31 - Integer.numberOfLeadingZeros(value)
 internal expect fun doubleFromParts(hi26: Int, low27: Int): Double
 
+@UseExperimental(ExperimentalStdlibApi::class)
+internal fun fastLog2(value: Int): Int = 31 - value.countLeadingZeroBits()
+
 /** Takes upper [bitCount] bits (0..32) from this number. */
 internal fun Int.takeUpperBits(bitCount: Int): Int =
     this.ushr(32 - bitCount) and (-bitCount).shr(31)