1// Copyright 2013 the V8 project authors. All rights reserved.
2// Use of this source code is governed by a BSD-style license that can be
3// found in the LICENSE file.
4
5#ifndef V8_BASE_UTILS_RANDOM_NUMBER_GENERATOR_H_
6#define V8_BASE_UTILS_RANDOM_NUMBER_GENERATOR_H_
7
8#include <unordered_set>
9#include <vector>
10
11#include "src/base/base-export.h"
12#include "src/base/macros.h"
13
14namespace v8 {
15namespace base {
16
17// -----------------------------------------------------------------------------
18// RandomNumberGenerator
19
20// This class is used to generate a stream of pseudo-random numbers. The class
21// uses a 64-bit seed, which is passed through MurmurHash3 to create two 64-bit
22// state values. This pair of state values is then used in xorshift128+.
23// The resulting stream of pseudo-random numbers has a period length of 2^128-1.
24// See Marsaglia: http://www.jstatsoft.org/v08/i14/paper
25// And Vigna: http://vigna.di.unimi.it/ftp/papers/xorshiftplus.pdf
26// NOTE: Any changes to the algorithm must be tested against TestU01.
27// Please find instructions for this in the internal repository.
28
29// If two instances of RandomNumberGenerator are created with the same seed, and
30// the same sequence of method calls is made for each, they will generate and
31// return identical sequences of numbers.
32// This class uses (probably) weak entropy by default, but it's sufficient,
33// because it is the responsibility of the embedder to install an entropy source
34// using v8::V8::SetEntropySource(), which provides reasonable entropy, see:
35// https://code.google.com/p/v8/issues/detail?id=2905
36// This class is neither reentrant nor threadsafe.
37
38class V8_BASE_EXPORT RandomNumberGenerator final {
39 public:
40 // EntropySource is used as a callback function when V8 needs a source of
41 // entropy.
42 using EntropySource = bool (*)(unsigned char* buffer, size_t buflen);
43 static void SetEntropySource(EntropySource entropy_source);
44
45 RandomNumberGenerator();
46 explicit RandomNumberGenerator(int64_t seed) { SetSeed(seed); }
47
48 // Returns the next pseudorandom, uniformly distributed int value from this
49 // random number generator's sequence. The general contract of |NextInt()| is
50 // that one int value is pseudorandomly generated and returned.
51 // All 2^32 possible integer values are produced with (approximately) equal
52 // probability.
53 V8_INLINE int NextInt() V8_WARN_UNUSED_RESULT { return Next(32); }
54
55 // Returns a pseudorandom, uniformly distributed int value between 0
56 // (inclusive) and the specified max value (exclusive), drawn from this random
57 // number generator's sequence. The general contract of |NextInt(int)| is that
58 // one int value in the specified range is pseudorandomly generated and
59 // returned. All max possible int values are produced with (approximately)
60 // equal probability.
61 int NextInt(int max) V8_WARN_UNUSED_RESULT;
62
63 // Returns the next pseudorandom, uniformly distributed boolean value from
64 // this random number generator's sequence. The general contract of
65 // |NextBoolean()| is that one boolean value is pseudorandomly generated and
66 // returned. The values true and false are produced with (approximately) equal
67 // probability.
68 V8_INLINE bool NextBool() V8_WARN_UNUSED_RESULT { return Next(1) != 0; }
69
70 // Returns the next pseudorandom, uniformly distributed double value between
71 // 0.0 and 1.0 from this random number generator's sequence.
72 // The general contract of |NextDouble()| is that one double value, chosen
73 // (approximately) uniformly from the range 0.0 (inclusive) to 1.0
74 // (exclusive), is pseudorandomly generated and returned.
75 double NextDouble() V8_WARN_UNUSED_RESULT;
76
77 // Returns the next pseudorandom, uniformly distributed int64 value from this
78 // random number generator's sequence. The general contract of |NextInt64()|
79 // is that one 64-bit int value is pseudorandomly generated and returned.
80 // All 2^64 possible integer values are produced with (approximately) equal
81 // probability.
82 int64_t NextInt64() V8_WARN_UNUSED_RESULT;
83
84 // Fills the elements of a specified array of bytes with random numbers.
85 void NextBytes(void* buffer, size_t buflen);
86
87 // Returns the next pseudorandom set of n unique uint64 values smaller than
88 // max.
89 // n must be less or equal to max.
90 std::vector<uint64_t> NextSample(uint64_t max,
91 size_t n) V8_WARN_UNUSED_RESULT;
92
93 // Returns the next pseudorandom set of n unique uint64 values smaller than
94 // max.
95 // n must be less or equal to max.
96 // max - |excluded| must be less or equal to n.
97 //
98 // Generates list of all possible values and removes random values from it
99 // until size reaches n.
100 std::vector<uint64_t> NextSampleSlow(
101 uint64_t max, size_t n,
102 const std::unordered_set<uint64_t>& excluded =
103 std::unordered_set<uint64_t>{}) V8_WARN_UNUSED_RESULT;
104
105 // Override the current ssed.
106 void SetSeed(int64_t seed);
107
108 int64_t initial_seed() const { return initial_seed_; }
109
110 // Static and exposed for external use.
111 static inline double ToDouble(uint64_t state0) {
112 // Exponent for double values for [1.0 .. 2.0)
113 static const uint64_t kExponentBits = uint64_t{0x3FF0000000000000};
114 uint64_t random = (state0 >> 12) | kExponentBits;
115 return bit_cast<double>(random) - 1;
116 }
117
118 // Static and exposed for external use.
119 static inline void XorShift128(uint64_t* state0, uint64_t* state1) {
120 uint64_t s1 = *state0;
121 uint64_t s0 = *state1;
122 *state0 = s0;
123 s1 ^= s1 << 23;
124 s1 ^= s1 >> 17;
125 s1 ^= s0;
126 s1 ^= s0 >> 26;
127 *state1 = s1;
128 }
129
130 static uint64_t MurmurHash3(uint64_t);
131
132 private:
133 static const int64_t kMultiplier = V8_2PART_UINT64_C(0x5, deece66d);
134 static const int64_t kAddend = 0xb;
135 static const int64_t kMask = V8_2PART_UINT64_C(0xffff, ffffffff);
136
137 int Next(int bits) V8_WARN_UNUSED_RESULT;
138
139 int64_t initial_seed_;
140 uint64_t state0_;
141 uint64_t state1_;
142};
143
144} // namespace base
145} // namespace v8
146
147#endif // V8_BASE_UTILS_RANDOM_NUMBER_GENERATOR_H_
148