| 25 |
|
|
| 26 |
|
package java.util; |
| 27 |
|
|
| 28 |
< |
import java.security.SecureRandom; |
| 29 |
< |
import java.net.InetAddress; |
| 28 |
> |
import java.net.NetworkInterface; |
| 29 |
|
import java.util.concurrent.atomic.AtomicLong; |
| 30 |
|
import java.util.function.IntConsumer; |
| 31 |
|
import java.util.function.LongConsumer; |
| 87 |
|
* @author Doug Lea |
| 88 |
|
* @since 1.8 |
| 89 |
|
*/ |
| 90 |
< |
public class SplittableRandom { |
| 90 |
> |
public final class SplittableRandom { |
| 91 |
|
|
| 92 |
|
/* |
| 93 |
|
* Implementation Overview. |
| 107 |
|
* Methods nextLong, nextInt, and derivatives do not return the |
| 108 |
|
* sequence (seed) values, but instead a hash-like bit-mix of |
| 109 |
|
* their bits, producing more independently distributed sequences. |
| 110 |
< |
* For nextLong, the mix64 bit-mixing function computes the same |
| 111 |
< |
* value as the "64-bit finalizer" function in Austin Appleby's |
| 112 |
< |
* MurmurHash3 algorithm. See |
| 113 |
< |
* http://code.google.com/p/smhasher/wiki/MurmurHash3 , which |
| 114 |
< |
* comments: "The constants for the finalizers were generated by a |
| 115 |
< |
* simple simulated-annealing algorithm, and both avalanche all |
| 116 |
< |
* bits of 'h' to within 0.25% bias." The mix32 function is |
| 118 |
< |
* equivalent to (int)(mix64(seed) >>> 32), but faster because it |
| 119 |
< |
* omits a step that doesn't contribute to result. |
| 110 |
> |
* For nextLong, the mix64 function is based on David Stafford's |
| 111 |
> |
* (http://zimbry.blogspot.com/2011/09/better-bit-mixing-improving-on.html) |
| 112 |
> |
* "Mix13" variant of the "64-bit finalizer" function in Austin |
| 113 |
> |
* Appleby's MurmurHash3 algorithm (see |
| 114 |
> |
* http://code.google.com/p/smhasher/wiki/MurmurHash3). The mix32 |
| 115 |
> |
* function is based on Stafford's Mix04 mix function, but returns |
| 116 |
> |
* the upper 32 bits cast as int. |
| 117 |
|
* |
| 118 |
|
* The split operation uses the current generator to form the seed |
| 119 |
|
* and gamma for another SplittableRandom. To conservatively |
| 120 |
|
* avoid potential correlations between seed and value generation, |
| 121 |
< |
* gamma selection (method nextGamma) uses the "Mix13" constants |
| 122 |
< |
* for MurmurHash3 described by David Stafford |
| 123 |
< |
* (http://zimbry.blogspot.com/2011/09/better-bit-mixing-improving-on.html) |
| 124 |
< |
* To avoid potential weaknesses in bit-mixing transformations, we |
| 125 |
< |
* restrict gammas to odd values with at least 12 and no more than |
| 126 |
< |
* 52 bits set. Rather than rejecting candidates with too few or |
| 127 |
< |
* too many bits set, method nextGamma flips some bits (which has |
| 128 |
< |
* the effect of mapping at most 4 to any given gamma value). |
| 132 |
< |
* This reduces the effective set of 64bit odd gamma values by |
| 133 |
< |
* about 2<sup>14</sup>, a very tiny percentage, and serves as an |
| 121 |
> |
* gamma selection (method mixGamma) uses different |
| 122 |
> |
* (Murmurhash3's) mix constants. To avoid potential weaknesses |
| 123 |
> |
* in bit-mixing transformations, we restrict gammas to odd values |
| 124 |
> |
* with at least 24 0-1 or 1-0 bit transitions. Rather than |
| 125 |
> |
* rejecting candidates with too few or too many bits set, method |
| 126 |
> |
* mixGamma flips some bits (which has the effect of mapping at |
| 127 |
> |
* most 4 to any given gamma value). This reduces the effective |
| 128 |
> |
* set of 64bit odd gamma values by about 2%, and serves as an |
| 129 |
|
* automated screening for sequence constant selection that is |
| 130 |
|
* left as an empirical decision in some other hashing and crypto |
| 131 |
|
* algorithms. |
| 136 |
|
* avalanching. |
| 137 |
|
* |
| 138 |
|
* The default (no-argument) constructor, in essence, invokes |
| 139 |
< |
* split() for a common "seeder" SplittableRandom. Unlike other |
| 140 |
< |
* cases, this split must be performed in a thread-safe manner, so |
| 141 |
< |
* we use an AtomicLong to represent the seed rather than use an |
| 142 |
< |
* explicit SplittableRandom. To bootstrap the seeder, we start |
| 143 |
< |
* off using a seed based on current time and host unless the |
| 144 |
< |
* java.util.secureRandomSeed property is set. This serves as a |
| 145 |
< |
* slimmed-down (and insecure) variant of SecureRandom that also |
| 146 |
< |
* avoids stalls that may occur when using /dev/random. |
| 139 |
> |
* split() for a common "defaultGen" SplittableRandom. Unlike |
| 140 |
> |
* other cases, this split must be performed in a thread-safe |
| 141 |
> |
* manner, so we use an AtomicLong to represent the seed rather |
| 142 |
> |
* than use an explicit SplittableRandom. To bootstrap the |
| 143 |
> |
* defaultGen, we start off using a seed based on current time and |
| 144 |
> |
* network interface address unless the java.util.secureRandomSeed |
| 145 |
> |
* property is set. This serves as a slimmed-down (and insecure) |
| 146 |
> |
* variant of SecureRandom that also avoids stalls that may occur |
| 147 |
> |
* when using /dev/random. |
| 148 |
|
* |
| 149 |
|
* It is a relatively simple matter to apply the basic design here |
| 150 |
|
* to use 128 bit seeds. However, emulating 128bit arithmetic and |
| 157 |
|
*/ |
| 158 |
|
|
| 159 |
|
/** |
| 160 |
< |
* The initial gamma value for (unsplit) SplittableRandoms. Must |
| 161 |
< |
* be odd with at least 12 and no more than 52 bits set. Currently |
| 166 |
< |
* set to the golden ratio scaled to 64bits. |
| 160 |
> |
* The golden ratio scaled to 64bits, used as the initial gamma |
| 161 |
> |
* value for (unsplit) SplittableRandoms. |
| 162 |
|
*/ |
| 163 |
< |
private static final long INITIAL_GAMMA = 0x9e3779b97f4a7c15L; |
| 163 |
> |
private static final long GOLDEN_GAMMA = 0x9e3779b97f4a7c15L; |
| 164 |
|
|
| 165 |
|
/** |
| 166 |
|
* The least non-zero value returned by nextDouble(). This value |
| 167 |
|
* is scaled by a random value of 53 bits to produce a result. |
| 168 |
|
*/ |
| 169 |
< |
private static final double DOUBLE_UNIT = 1.0 / (1L << 53); |
| 169 |
> |
private static final double DOUBLE_UNIT = 0x1.0p-53; // 1.0 / (1L << 53); |
| 170 |
|
|
| 171 |
|
/** |
| 172 |
|
* The seed. Updated only via method nextSeed. |
| 187 |
|
} |
| 188 |
|
|
| 189 |
|
/** |
| 190 |
< |
* Computes MurmurHash3 64bit mix function. |
| 190 |
> |
* Computes Stafford variant 13 of 64bit mix function. |
| 191 |
|
*/ |
| 192 |
|
private static long mix64(long z) { |
| 193 |
< |
z = (z ^ (z >>> 33)) * 0xff51afd7ed558ccdL; |
| 194 |
< |
z = (z ^ (z >>> 33)) * 0xc4ceb9fe1a85ec53L; |
| 195 |
< |
return z ^ (z >>> 33); |
| 193 |
> |
z = (z ^ (z >>> 30)) * 0xbf58476d1ce4e5b9L; |
| 194 |
> |
z = (z ^ (z >>> 27)) * 0x94d049bb133111ebL; |
| 195 |
> |
return z ^ (z >>> 31); |
| 196 |
|
} |
| 197 |
|
|
| 198 |
|
/** |
| 199 |
< |
* Returns the 32 high bits of mix64(z) as int. |
| 199 |
> |
* Returns the 32 high bits of Stafford variant 4 mix64 function as int. |
| 200 |
|
*/ |
| 201 |
|
private static int mix32(long z) { |
| 202 |
< |
z = (z ^ (z >>> 33)) * 0xff51afd7ed558ccdL; |
| 203 |
< |
return (int)(((z ^ (z >>> 33)) * 0xc4ceb9fe1a85ec53L) >>> 32); |
| 202 |
> |
z = (z ^ (z >>> 33)) * 0x62a9d9ed799705f5L; |
| 203 |
> |
return (int)(((z ^ (z >>> 28)) * 0xcb24d0a5c88c35b3L) >>> 32); |
| 204 |
|
} |
| 205 |
|
|
| 206 |
|
/** |
| 207 |
|
* Returns the gamma value to use for a new split instance. |
| 208 |
|
*/ |
| 209 |
< |
private static long nextGamma(long z) { |
| 210 |
< |
z = (z ^ (z >>> 30)) * 0xbf58476d1ce4e5b9L; // Stafford "Mix13" |
| 211 |
< |
z = (z ^ (z >>> 27)) * 0x94d049bb133111ebL; |
| 212 |
< |
z = (z ^ (z >>> 31)) | 1L; // force to be odd |
| 213 |
< |
int n = Long.bitCount(z); // ensure enough 0 and 1 bits |
| 214 |
< |
return (n < 12 || n > 52) ? z ^ 0xaaaaaaaaaaaaaaaaL : z; |
| 209 |
> |
private static long mixGamma(long z) { |
| 210 |
> |
z = (z ^ (z >>> 33)) * 0xff51afd7ed558ccdL; // MurmurHash3 mix constants |
| 211 |
> |
z = (z ^ (z >>> 33)) * 0xc4ceb9fe1a85ec53L; |
| 212 |
> |
z = (z ^ (z >>> 33)) | 1L; // force to be odd |
| 213 |
> |
int n = Long.bitCount(z ^ (z >>> 1)); // ensure enough transitions |
| 214 |
> |
return (n < 24) ? z ^ 0xaaaaaaaaaaaaaaaaL : z; |
| 215 |
|
} |
| 216 |
|
|
| 217 |
|
/** |
| 224 |
|
/** |
| 225 |
|
* The seed generator for default constructors. |
| 226 |
|
*/ |
| 227 |
< |
private static final AtomicLong seeder = new AtomicLong(initialSeed()); |
| 227 |
> |
private static final AtomicLong defaultGen = new AtomicLong(initialSeed()); |
| 228 |
|
|
| 229 |
|
private static long initialSeed() { |
| 230 |
< |
try { // ignore exceptions in accessing/parsing properties |
| 231 |
< |
String pp = System.getProperty |
| 232 |
< |
("java.util.secureRandomSeed"); |
| 233 |
< |
if (pp != null && pp.equalsIgnoreCase("true")) { |
| 234 |
< |
byte[] seedBytes = java.security.SecureRandom.getSeed(8); |
| 235 |
< |
long s = (long)(seedBytes[0]) & 0xffL; |
| 236 |
< |
for (int i = 1; i < 8; ++i) |
| 237 |
< |
s = (s << 8) | ((long)(seedBytes[i]) & 0xffL); |
| 238 |
< |
return s; |
| 244 |
< |
} |
| 245 |
< |
} catch (Exception ignore) { |
| 230 |
> |
String pp = java.security.AccessController.doPrivileged( |
| 231 |
> |
new sun.security.action.GetPropertyAction( |
| 232 |
> |
"java.util.secureRandomSeed")); |
| 233 |
> |
if (pp != null && pp.equalsIgnoreCase("true")) { |
| 234 |
> |
byte[] seedBytes = java.security.SecureRandom.getSeed(8); |
| 235 |
> |
long s = (long)(seedBytes[0]) & 0xffL; |
| 236 |
> |
for (int i = 1; i < 8; ++i) |
| 237 |
> |
s = (s << 8) | ((long)(seedBytes[i]) & 0xffL); |
| 238 |
> |
return s; |
| 239 |
|
} |
| 240 |
< |
int hh = 0; // hashed host address |
| 240 |
> |
long h = 0L; |
| 241 |
|
try { |
| 242 |
< |
hh = InetAddress.getLocalHost().hashCode(); |
| 242 |
> |
Enumeration<NetworkInterface> ifcs = |
| 243 |
> |
NetworkInterface.getNetworkInterfaces(); |
| 244 |
> |
boolean retry = false; // retry once if getHardwareAddress is null |
| 245 |
> |
while (ifcs.hasMoreElements()) { |
| 246 |
> |
NetworkInterface ifc = ifcs.nextElement(); |
| 247 |
> |
if (!ifc.isVirtual()) { // skip fake addresses |
| 248 |
> |
byte[] bs = ifc.getHardwareAddress(); |
| 249 |
> |
if (bs != null) { |
| 250 |
> |
int n = bs.length; |
| 251 |
> |
int m = Math.min(n >>> 1, 4); |
| 252 |
> |
for (int i = 0; i < m; ++i) |
| 253 |
> |
h = (h << 16) ^ (bs[i] << 8) ^ bs[n-1-i]; |
| 254 |
> |
if (m < 4) |
| 255 |
> |
h = (h << 8) ^ bs[n-1-m]; |
| 256 |
> |
h = mix64(h); |
| 257 |
> |
break; |
| 258 |
> |
} |
| 259 |
> |
else if (!retry) |
| 260 |
> |
retry = true; |
| 261 |
> |
else |
| 262 |
> |
break; |
| 263 |
> |
} |
| 264 |
> |
} |
| 265 |
|
} catch (Exception ignore) { |
| 266 |
|
} |
| 267 |
< |
return (mix64((((long)hh) << 32) ^ System.currentTimeMillis()) ^ |
| 267 |
> |
return (h ^ mix64(System.currentTimeMillis()) ^ |
| 268 |
|
mix64(System.nanoTime())); |
| 269 |
|
} |
| 270 |
|
|
| 392 |
|
* @param seed the initial seed |
| 393 |
|
*/ |
| 394 |
|
public SplittableRandom(long seed) { |
| 395 |
< |
this(seed, INITIAL_GAMMA); |
| 395 |
> |
this(seed, GOLDEN_GAMMA); |
| 396 |
|
} |
| 397 |
|
|
| 398 |
|
/** |
| 401 |
|
* of those of any other instances in the current program; and |
| 402 |
|
* may, and typically does, vary across program invocations. |
| 403 |
|
*/ |
| 404 |
< |
public SplittableRandom() { // emulate seeder.split() |
| 405 |
< |
this.gamma = nextGamma(this.seed = seeder.addAndGet(INITIAL_GAMMA)); |
| 404 |
> |
public SplittableRandom() { // emulate defaultGen.split() |
| 405 |
> |
long s = defaultGen.getAndAdd(2 * GOLDEN_GAMMA); |
| 406 |
> |
this.seed = mix64(s); |
| 407 |
> |
this.gamma = mixGamma(s + GOLDEN_GAMMA); |
| 408 |
|
} |
| 409 |
|
|
| 410 |
|
/** |
| 422 |
|
* @return the new SplittableRandom instance |
| 423 |
|
*/ |
| 424 |
|
public SplittableRandom split() { |
| 425 |
< |
long s = nextSeed(); |
| 409 |
< |
return new SplittableRandom(s, nextGamma(s)); |
| 425 |
> |
return new SplittableRandom(nextLong(), mixGamma(nextSeed())); |
| 426 |
|
} |
| 427 |
|
|
| 428 |
|
/** |
