Package it.unimi.dsi.util
Miscellaneaous utility classes.
Pseudorandom number generators
We provide a number of fast, high-quality PRNGs with different features. You can get detailed information about the generators at our PRNG page, together with a reasoned guide to the choice of the generator that's right for you.
A table summarizing timings is provided below. The timings were measured on an
Intel® Core™ i7-8700B CPU @3.20GHz using
JMH microbenchmarks. The JMH timings were decreased by 1ns, as
using the low-level perfasm profiler the JMH overhead was estimated at ≈1ns per call.
Random
| ThreadLocalRandom
| SplittableRandom
| SplitMix64
| | | | | | | | |
|---|---|---|---|---|---|---|---|---|---|---|---|
| nextLong() | 14.419 | 1.252 | 1.283 | 1.241 | 1.428 | 1.574 | 1.295 | 1.738 | 1.884 | 1.653 | 1.901 |
| nextInt(100000) | 6.715 | 2.045 | 2.499 | 2.543 | 2.336 | 2.594 | 1.202 | 2.607 | 2.954 | 2.367 | 3.119 |
| nextDouble() | 14.458 | 1.876 | 2.161 | 2.176 | 1.918 | 2.219 | 1.853 | 2.304 | 2.503 | 2.112 | 2.755 |
Note that generators that are extremely fast in C, such as xoshiro256+, do not perform particularly well in Java, most likely
because of the cost of accessing variables, which rises as the size of the state space grows. Indeed,
smaller-state generators are faster. Moreover, generators based on the ++
scrambler are slightly faster than those based on the ** scrambler, contrarily to what happens in C.
For each generator, we provide a version that extends Random, overriding (as usual) the next(int) method. Nonetheless,
since the generators are all inherently 64-bit also nextInt(), nextFloat(),
nextLong(), nextDouble(), nextBoolean()
and nextBytes(byte[]) have been overridden for speed (preserving, of course, Random's semantics).
If you do not need an instance of Random, or if you need a RandomGenerator to use
with Commons Math, there is for each generator a corresponding RandomGenerator
implementation, which indeed we suggest to use in general if you do not need a generator implementing Random.
-
Interface Summary Interface Description PrefixMap<S extends CharSequence> A map from prefixes to string intervals (and possibly vice versa).StringMap<S extends CharSequence> A map from strings to numbers (and possibly vice versa). -
Class Summary Class Description AbstractPrefixMap An abstract implementation of a prefix map.BloomFilter<T> A Bloom filter.ByteBufferLongBigList A bridge between byte buffers and long big lists.CircularCharArrayBuffer A circular char buffer that can be used to implement a sliding window over a text.FrontCodedStringList Compact storage of strings using front-coding compression (a.k.a. compression by prefix omission).HyperLogLogCounterArray An array of approximate sets each represented using a HyperLogLog counter.ImmutableBinaryTrie<T> An immutable implementation of binary tries.ImmutableBinaryTrie.Node A node in the trie.ImmutableExternalPrefixMap An immutable prefix map mostly stored in external memory.Interval An interval of integers.Intervals A class providing static methods and objects that do useful things with intervals.KahanSummation Kahan's summation algorithm encapsulated in an object.LiterallySignedStringMap A string map based on a function signed using the original list of strings.LongInterval An interval of longs.LongIntervals A class providing static methods and objects that do useful things with intervals.PermutedFrontCodedStringList AFrontCodedStringListwhose indices are permuted.Properties An extension ofPropertiesConfigurationproviding setters for primitive types, a simpler way to save preferences and transparent handling ofEnumlowercased keys.SemiExternalGammaList Provides semi-external random access to a list of γ-encoded integers.ShiftAddXorSignedStringMap Deprecated. There are much better and faster hash functions.SplitMix64Random A fast, high-quality, non-splittable version of the SplitMix pseudorandom number generator used bySplittableRandom.SplitMix64RandomGenerator A fast, high-quality, non-splittable version of the SplitMix pseudorandom number generator used bySplittableRandom.StringMaps A class providing static methods and objects that do useful things with string maps and prefix maps.StringMaps.SynchronizedPrefixMap<S extends CharSequence> StringMaps.SynchronizedStringMap<S extends CharSequence> TernaryIntervalSearchTree Ternary interval search trees.TextPattern QuickSearch matching against a constant string.XoRoShiRo128PlusPlusRandom A fast, all-purpose, rock-solid, small-state pseudorandom number generator.XoRoShiRo128PlusPlusRandomGenerator A fast, all-purpose, rock-solid, small-state pseudorandom number generator.XoRoShiRo128PlusRandom A fast, high-quality pseudorandom number generator for floating-point generation.XoRoShiRo128PlusRandomGenerator A fast, high-quality pseudorandom number generator for floating-point generation.XoRoShiRo128StarStarRandom A fast, all-purpose, rock-solid, small-state pseudorandom number generator.XoRoShiRo128StarStarRandomGenerator A fast, all-purpose, rock-solid, small-state pseudorandom number generator.XorShift1024StarPhiRandom A fast, high-quality pseudorandom number generator that combines a long-period instance of George Marsaglia's Xorshift generators (described in “Xorshift RNGs”, Journal of Statistical Software, 8:1−6, 2003) with a multiplication.XorShift1024StarPhiRandomGenerator A fast, high-quality pseudorandom number generator that combines a long-period instance of George Marsaglia's Xorshift generators (described in “Xorshift RNGs”, Journal of Statistical Software, 8:1−6, 2003) with a multiplication.XorShift1024StarRandom Deprecated. Please useXorShift1024StarPhiRandominstead.XorShift1024StarRandomGenerator Deprecated. Please useXorShift1024StarPhiRandomGeneratorinstead.XorShift128PlusRandom Deprecated. Please useXoRoShiRo128PlusRandominstead.XorShift128PlusRandomGenerator Deprecated. Please useXoRoShiRo128PlusRandomGeneratorinstead.XorShift64StarRandom Deprecated. UseSplitMix64Randominstead.XorShift64StarRandomGenerator Deprecated. UseSplitMix64RandomGeneratorinstead.XoShiRo256PlusPlusRandom A fast, all-purpose, rock-solid pseudorandom number generator.XoShiRo256PlusPlusRandomGenerator A fast, all-purpose, rock-solid pseudorandom number generator.XoShiRo256PlusRandom A fast, rock-solid pseudorandom number generator for floating-point generation.XoShiRo256PlusRandomGenerator A fast, rock-solid pseudorandom number generator for floating-point generation.XoShiRo256StarStarRandom A fast, all-purpose, rock-solid pseudorandom number generator.XoShiRo256StarStarRandomGenerator A fast, all-purpose, rock-solid pseudorandom number generator.