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package java.util; |
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import java.security.SecureRandom; |
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import java.net.NetworkInterface; |
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import java.util.Enumeration; |
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import java.util.concurrent.atomic.AtomicLong; |
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import java.util.function.IntConsumer; |
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import java.util.function.LongConsumer; |
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* @author Doug Lea |
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* @since 1.8 |
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*/ |
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< |
public class SplittableRandom { |
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public final class SplittableRandom { |
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/* |
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* Implementation Overview. |
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* For nextLong, the mix64 function is based on David Stafford's |
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* (http://zimbry.blogspot.com/2011/09/better-bit-mixing-improving-on.html) |
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* "Mix13" variant of the "64-bit finalizer" function in Austin |
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* Appleby's MurmurHash3 algorithm See |
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* http://code.google.com/p/smhasher/wiki/MurmurHash3 . The mix32 |
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* Appleby's MurmurHash3 algorithm (see |
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* http://code.google.com/p/smhasher/wiki/MurmurHash3). The mix32 |
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* function is based on Stafford's Mix04 mix function, but returns |
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* the upper 32 bits cast as int. |
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* |
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* other cases, this split must be performed in a thread-safe |
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* manner, so we use an AtomicLong to represent the seed rather |
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* than use an explicit SplittableRandom. To bootstrap the |
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* defaultGen, we start off using a seed based on current time and |
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* network interface address unless the java.util.secureRandomSeed |
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* property is set. This serves as a slimmed-down (and insecure) |
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* variant of SecureRandom that also avoids stalls that may occur |
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* when using /dev/random. |
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* defaultGen, we start off using a seed based on current time |
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* unless the java.util.secureRandomSeed property is set. This |
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* serves as a slimmed-down (and insecure) variant of SecureRandom |
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* that also avoids stalls that may occur when using /dev/random. |
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* |
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* It is a relatively simple matter to apply the basic design here |
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* to use 128 bit seeds. However, emulating 128bit arithmetic and |
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* The least non-zero value returned by nextDouble(). This value |
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* is scaled by a random value of 53 bits to produce a result. |
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*/ |
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private static final double DOUBLE_ULP = 1.0 / (1L << 53); |
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private static final double DOUBLE_UNIT = 0x1.0p-53; // 1.0 / (1L << 53); |
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/** |
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* The seed. Updated only via method nextSeed. |
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* Computes Stafford variant 13 of 64bit mix function. |
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*/ |
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private static long mix64(long z) { |
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z *= 0xbf58476d1ce4e5b9L; |
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z = (z ^ (z >>> 32)) * 0x94d049bb133111ebL; |
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return z ^ (z >>> 32); |
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z = (z ^ (z >>> 30)) * 0xbf58476d1ce4e5b9L; |
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z = (z ^ (z >>> 27)) * 0x94d049bb133111ebL; |
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return z ^ (z >>> 31); |
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} |
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/** |
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* Returns the 32 high bits of Stafford variant 4 mix64 function as int. |
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*/ |
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private static int mix32(long z) { |
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z *= 0x62a9d9ed799705f5L; |
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z = (z ^ (z >>> 33)) * 0x62a9d9ed799705f5L; |
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return (int)(((z ^ (z >>> 28)) * 0xcb24d0a5c88c35b3L) >>> 32); |
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} |
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* Returns the gamma value to use for a new split instance. |
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*/ |
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private static long mixGamma(long z) { |
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z *= 0xff51afd7ed558ccdL; // MurmurHash3 mix constants |
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z = (z ^ (z >>> 33)) * 0xff51afd7ed558ccdL; // MurmurHash3 mix constants |
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z = (z ^ (z >>> 33)) * 0xc4ceb9fe1a85ec53L; |
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z = (z ^ (z >>> 33)) | 1L; // force to be odd |
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int n = Long.bitCount(z ^ (z >>> 1)); // ensure enough transitions |
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s = (s << 8) | ((long)(seedBytes[i]) & 0xffL); |
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return s; |
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} |
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long h = 0L; |
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try { |
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Enumeration<NetworkInterface> ifcs = |
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NetworkInterface.getNetworkInterfaces(); |
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boolean retry = false; // retry once if getHardwareAddress is null |
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while (ifcs.hasMoreElements()) { |
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NetworkInterface ifc = ifcs.nextElement(); |
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if (!ifc.isVirtual()) { // skip fake addresses |
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byte[] bs = ifc.getHardwareAddress(); |
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if (bs != null) { |
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int n = bs.length; |
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int m = Math.min(n >>> 1, 4); |
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for (int i = 0; i < m; ++i) |
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h = (h << 16) ^ (bs[i] << 8) ^ bs[n-1-i]; |
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if (m < 4) |
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h = (h << 8) ^ bs[n-1-m]; |
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h = mix64(h); |
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break; |
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} |
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else if (!retry) |
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retry = true; |
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else |
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break; |
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} |
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} |
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} catch (Exception ignore) { |
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} |
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return (h ^ mix64(System.currentTimeMillis()) ^ |
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return (mix64(System.currentTimeMillis()) ^ |
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mix64(System.nanoTime())); |
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} |
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* @return a pseudorandom value |
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*/ |
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final double internalNextDouble(double origin, double bound) { |
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double r = (nextLong() >>> 11) * DOUBLE_ULP; |
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double r = (nextLong() >>> 11) * DOUBLE_UNIT; |
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if (origin < bound) { |
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r = r * (bound - origin) + origin; |
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if (r >= bound) // correct for rounding |
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* may, and typically does, vary across program invocations. |
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*/ |
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public SplittableRandom() { // emulate defaultGen.split() |
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long s = defaultGen.getAndAdd(2*GOLDEN_GAMMA); |
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long s = defaultGen.getAndAdd(2 * GOLDEN_GAMMA); |
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this.seed = mix64(s); |
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this.gamma = mixGamma(s + GOLDEN_GAMMA); |
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} |
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* (inclusive) and one (exclusive) |
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*/ |
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public double nextDouble() { |
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return (mix64(nextSeed()) >>> 11) * DOUBLE_ULP; |
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return (mix64(nextSeed()) >>> 11) * DOUBLE_UNIT; |
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} |
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/** |
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public double nextDouble(double bound) { |
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if (!(bound > 0.0)) |
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throw new IllegalArgumentException(BadBound); |
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double result = (mix64(nextSeed()) >>> 11) * DOUBLE_ULP * bound; |
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double result = (mix64(nextSeed()) >>> 11) * DOUBLE_UNIT * bound; |
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return (result < bound) ? result : // correct for rounding |
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Double.longBitsToDouble(Double.doubleToLongBits(bound) - 1); |
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} |
