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package java.util; |
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import java.security.SecureRandom; |
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import java.net.InetAddress; |
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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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* Methods nextLong, nextInt, and derivatives do not return the |
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* sequence (seed) values, but instead a hash-like bit-mix of |
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* their bits, producing more independently distributed sequences. |
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* For nextLong, the mix64 bit-mixing function computes the same |
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* value as the "64-bit finalizer" function in Austin Appleby's |
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* MurmurHash3 algorithm. See |
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* http://code.google.com/p/smhasher/wiki/MurmurHash3 , which |
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* comments: "The constants for the finalizers were generated by a |
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* simple simulated-annealing algorithm, and both avalanche all |
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* bits of 'h' to within 0.25% bias." The mix32 function is |
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* equivalent to (int)(mix64(seed) >>> 32), but faster because it |
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* omits a step that doesn't contribute to result. |
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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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* 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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* The split operation uses the current generator to form the seed |
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* and gamma for another SplittableRandom. To conservatively |
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* avoid potential correlations between seed and value generation, |
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* gamma selection (method nextGamma) uses the "Mix13" constants |
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* for MurmurHash3 described by David Stafford |
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* (http://zimbry.blogspot.com/2011/09/better-bit-mixing-improving-on.html) |
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* To avoid potential weaknesses in bit-mixing transformations, we |
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* restrict gammas to odd values with at least 12 and no more than |
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* 52 bits set. Rather than rejecting candidates with too few or |
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* too many bits set, method nextGamma flips some bits (which has |
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* the effect of mapping at most 4 to any given gamma value). |
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* This reduces the effective set of 64bit odd gamma values by |
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* about 2<sup>14</sup>, a very tiny percentage, and serves as an |
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* gamma selection (method mixGamma) uses different |
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* (Murmurhash3's) mix constants. To avoid potential weaknesses |
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* in bit-mixing transformations, we restrict gammas to odd values |
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* with at least 24 0-1 or 1-0 bit transitions. Rather than |
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* rejecting candidates with too few or too many bits set, method |
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* mixGamma flips some bits (which has the effect of mapping at |
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* most 4 to any given gamma value). This reduces the effective |
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* set of 64bit odd gamma values by about 2%, and serves as an |
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* automated screening for sequence constant selection that is |
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* left as an empirical decision in some other hashing and crypto |
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* algorithms. |
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* avalanching. |
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* |
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* The default (no-argument) constructor, in essence, invokes |
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* split() for a common "seeder" SplittableRandom. Unlike other |
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* cases, this split must be performed in a thread-safe manner, so |
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* we use an AtomicLong to represent the seed rather than use an |
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* explicit SplittableRandom. To bootstrap the seeder, we start |
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* off using a seed based on current time and host unless the |
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* java.util.secureRandomSeed property is set. This serves as a |
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* slimmed-down (and insecure) variant of SecureRandom that also |
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* avoids stalls that may occur when using /dev/random. |
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* split() for a common "defaultGen" SplittableRandom. Unlike |
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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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* |
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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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*/ |
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/** |
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* The initial gamma value for (unsplit) SplittableRandoms. Must |
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* be odd with at least 12 and no more than 52 bits set. Currently |
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* set to the golden ratio scaled to 64bits. |
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* The golden ratio scaled to 64bits, used as the initial gamma |
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* value for (unsplit) SplittableRandoms. |
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*/ |
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private static final long INITIAL_GAMMA = 0x9e3779b97f4a7c15L; |
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private static final long GOLDEN_GAMMA = 0x9e3779b97f4a7c15L; |
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/** |
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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_UNIT = 1.0 / (1L << 53); |
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private static final double DOUBLE_ULP = 1.0 / (1L << 53); |
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/** |
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* The seed. Updated only via method nextSeed. |
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} |
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/** |
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* Computes MurmurHash3 64bit mix function. |
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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 = (z ^ (z >>> 33)) * 0xff51afd7ed558ccdL; |
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z = (z ^ (z >>> 33)) * 0xc4ceb9fe1a85ec53L; |
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return z ^ (z >>> 33); |
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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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} |
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private static long xmix64(long z) { |
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z *= 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 mix64(z) as int. |
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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 = (z ^ (z >>> 33)) * 0xff51afd7ed558ccdL; |
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return (int)(((z ^ (z >>> 33)) * 0xc4ceb9fe1a85ec53L) >>> 32); |
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z *= 0x62a9d9ed799705f5L; |
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return (int)(((z ^ (z >>> 28)) * 0xcb24d0a5c88c35b3L) >>> 32); |
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} |
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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 nextGamma(long z) { |
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z = (z ^ (z >>> 30)) * 0xbf58476d1ce4e5b9L; // Stafford "Mix13" |
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z = (z ^ (z >>> 27)) * 0x94d049bb133111ebL; |
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z = (z ^ (z >>> 31)) | 1L; // force to be odd |
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int n = Long.bitCount(z); // ensure enough 0 and 1 bits |
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return (n < 12 || n > 52) ? z ^ 0xaaaaaaaaaaaaaaaaL : z; |
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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)) * 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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return (n < 24) ? z ^ 0xaaaaaaaaaaaaaaaaL : z; |
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} |
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/** |
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/** |
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* The seed generator for default constructors. |
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*/ |
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private static final AtomicLong seeder = new AtomicLong(initialSeed()); |
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private static final AtomicLong defaultGen = new AtomicLong(initialSeed()); |
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private static long initialSeed() { |
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try { // ignore exceptions in accessing/parsing properties |
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String pp = System.getProperty |
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("java.util.secureRandomSeed"); |
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if (pp != null && pp.equalsIgnoreCase("true")) { |
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byte[] seedBytes = java.security.SecureRandom.getSeed(8); |
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long s = (long)(seedBytes[0]) & 0xffL; |
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for (int i = 1; i < 8; ++i) |
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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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} catch (Exception ignore) { |
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String pp = java.security.AccessController.doPrivileged( |
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new sun.security.action.GetPropertyAction( |
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"java.util.secureRandomSeed")); |
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if (pp != null && pp.equalsIgnoreCase("true")) { |
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byte[] seedBytes = java.security.SecureRandom.getSeed(8); |
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long s = (long)(seedBytes[0]) & 0xffL; |
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for (int i = 1; i < 8; ++i) |
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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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int hh = 0; // hashed host address |
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long h = 0L; |
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try { |
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hh = InetAddress.getLocalHost().hashCode(); |
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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 (mix64((((long)hh) << 32) ^ System.currentTimeMillis()) ^ |
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return (h ^ 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_UNIT; |
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double r = (nextLong() >>> 11) * DOUBLE_ULP; |
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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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* @param seed the initial seed |
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*/ |
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public SplittableRandom(long seed) { |
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this(seed, INITIAL_GAMMA); |
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this(seed, GOLDEN_GAMMA); |
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} |
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/** |
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* of those of any other instances in the current program; and |
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* may, and typically does, vary across program invocations. |
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*/ |
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public SplittableRandom() { // emulate seeder.split() |
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this.gamma = nextGamma(this.seed = seeder.addAndGet(INITIAL_GAMMA)); |
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public SplittableRandom() { // emulate defaultGen.split() |
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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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/** |
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* @return the new SplittableRandom instance |
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*/ |
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public SplittableRandom split() { |
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long s = nextSeed(); |
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return new SplittableRandom(s, nextGamma(s)); |
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return new SplittableRandom(nextLong(), mixGamma(nextSeed())); |
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} |
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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_UNIT; |
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return (mix64(nextSeed()) >>> 11) * DOUBLE_ULP; |
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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_UNIT * bound; |
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double result = (mix64(nextSeed()) >>> 11) * DOUBLE_ULP * 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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} |
