Ben Murdoch | b8a8cc1 | 2014-11-26 15:28:44 +0000 | [diff] [blame] | 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 "src/base/macros.h" |
| 9 | |
| 10 | namespace v8 { |
| 11 | namespace base { |
| 12 | |
| 13 | // ----------------------------------------------------------------------------- |
| 14 | // RandomNumberGenerator |
Ben Murdoch | 4a90d5f | 2016-03-22 12:00:34 +0000 | [diff] [blame] | 15 | |
| 16 | // This class is used to generate a stream of pseudo-random numbers. The class |
| 17 | // uses a 64-bit seed, which is passed through MurmurHash3 to create two 64-bit |
| 18 | // state values. This pair of state values is then used in xorshift128+. |
| 19 | // The resulting stream of pseudo-random numbers has a period length of 2^128-1. |
| 20 | // See Marsaglia: http://www.jstatsoft.org/v08/i14/paper |
| 21 | // And Vigna: http://vigna.di.unimi.it/ftp/papers/xorshiftplus.pdf |
| 22 | // NOTE: Any changes to the algorithm must be tested against TestU01. |
| 23 | // Please find instructions for this in the internal repository. |
| 24 | |
Ben Murdoch | b8a8cc1 | 2014-11-26 15:28:44 +0000 | [diff] [blame] | 25 | // If two instances of RandomNumberGenerator are created with the same seed, and |
| 26 | // the same sequence of method calls is made for each, they will generate and |
| 27 | // return identical sequences of numbers. |
| 28 | // This class uses (probably) weak entropy by default, but it's sufficient, |
| 29 | // because it is the responsibility of the embedder to install an entropy source |
| 30 | // using v8::V8::SetEntropySource(), which provides reasonable entropy, see: |
| 31 | // https://code.google.com/p/v8/issues/detail?id=2905 |
| 32 | // This class is neither reentrant nor threadsafe. |
| 33 | |
Ben Murdoch | 4a90d5f | 2016-03-22 12:00:34 +0000 | [diff] [blame] | 34 | class RandomNumberGenerator final { |
Ben Murdoch | b8a8cc1 | 2014-11-26 15:28:44 +0000 | [diff] [blame] | 35 | public: |
| 36 | // EntropySource is used as a callback function when V8 needs a source of |
| 37 | // entropy. |
| 38 | typedef bool (*EntropySource)(unsigned char* buffer, size_t buflen); |
| 39 | static void SetEntropySource(EntropySource entropy_source); |
| 40 | |
| 41 | RandomNumberGenerator(); |
| 42 | explicit RandomNumberGenerator(int64_t seed) { SetSeed(seed); } |
| 43 | |
| 44 | // Returns the next pseudorandom, uniformly distributed int value from this |
| 45 | // random number generator's sequence. The general contract of |NextInt()| is |
| 46 | // that one int value is pseudorandomly generated and returned. |
| 47 | // All 2^32 possible integer values are produced with (approximately) equal |
| 48 | // probability. |
| 49 | V8_INLINE int NextInt() WARN_UNUSED_RESULT { |
| 50 | return Next(32); |
| 51 | } |
| 52 | |
| 53 | // Returns a pseudorandom, uniformly distributed int value between 0 |
| 54 | // (inclusive) and the specified max value (exclusive), drawn from this random |
| 55 | // number generator's sequence. The general contract of |NextInt(int)| is that |
| 56 | // one int value in the specified range is pseudorandomly generated and |
| 57 | // returned. All max possible int values are produced with (approximately) |
| 58 | // equal probability. |
| 59 | int NextInt(int max) WARN_UNUSED_RESULT; |
| 60 | |
| 61 | // Returns the next pseudorandom, uniformly distributed boolean value from |
| 62 | // this random number generator's sequence. The general contract of |
| 63 | // |NextBoolean()| is that one boolean value is pseudorandomly generated and |
| 64 | // returned. The values true and false are produced with (approximately) equal |
| 65 | // probability. |
| 66 | V8_INLINE bool NextBool() WARN_UNUSED_RESULT { |
| 67 | return Next(1) != 0; |
| 68 | } |
| 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() WARN_UNUSED_RESULT; |
| 76 | |
Emily Bernier | d0a1eb7 | 2015-03-24 16:35:39 -0400 | [diff] [blame] | 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() WARN_UNUSED_RESULT; |
| 83 | |
Ben Murdoch | b8a8cc1 | 2014-11-26 15:28:44 +0000 | [diff] [blame] | 84 | // Fills the elements of a specified array of bytes with random numbers. |
| 85 | void NextBytes(void* buffer, size_t buflen); |
| 86 | |
| 87 | // Override the current ssed. |
| 88 | void SetSeed(int64_t seed); |
| 89 | |
| 90 | int64_t initial_seed() const { return initial_seed_; } |
| 91 | |
Ben Murdoch | 4a90d5f | 2016-03-22 12:00:34 +0000 | [diff] [blame] | 92 | // Static and exposed for external use. |
| 93 | static inline double ToDouble(uint64_t state0, uint64_t state1) { |
| 94 | // Exponent for double values for [1.0 .. 2.0) |
| 95 | static const uint64_t kExponentBits = V8_UINT64_C(0x3FF0000000000000); |
| 96 | static const uint64_t kMantissaMask = V8_UINT64_C(0x000FFFFFFFFFFFFF); |
| 97 | uint64_t random = ((state0 + state1) & kMantissaMask) | kExponentBits; |
| 98 | return bit_cast<double>(random) - 1; |
| 99 | } |
| 100 | |
| 101 | // Static and exposed for external use. |
| 102 | static inline void XorShift128(uint64_t* state0, uint64_t* state1) { |
| 103 | uint64_t s1 = *state0; |
| 104 | uint64_t s0 = *state1; |
| 105 | *state0 = s0; |
| 106 | s1 ^= s1 << 23; |
| 107 | s1 ^= s1 >> 17; |
| 108 | s1 ^= s0; |
| 109 | s1 ^= s0 >> 26; |
| 110 | *state1 = s1; |
| 111 | } |
| 112 | |
Ben Murdoch | b8a8cc1 | 2014-11-26 15:28:44 +0000 | [diff] [blame] | 113 | private: |
| 114 | static const int64_t kMultiplier = V8_2PART_UINT64_C(0x5, deece66d); |
| 115 | static const int64_t kAddend = 0xb; |
| 116 | static const int64_t kMask = V8_2PART_UINT64_C(0xffff, ffffffff); |
| 117 | |
| 118 | int Next(int bits) WARN_UNUSED_RESULT; |
| 119 | |
Ben Murdoch | 4a90d5f | 2016-03-22 12:00:34 +0000 | [diff] [blame] | 120 | static uint64_t MurmurHash3(uint64_t); |
| 121 | |
Ben Murdoch | b8a8cc1 | 2014-11-26 15:28:44 +0000 | [diff] [blame] | 122 | int64_t initial_seed_; |
Ben Murdoch | 4a90d5f | 2016-03-22 12:00:34 +0000 | [diff] [blame] | 123 | uint64_t state0_; |
| 124 | uint64_t state1_; |
Ben Murdoch | b8a8cc1 | 2014-11-26 15:28:44 +0000 | [diff] [blame] | 125 | }; |
| 126 | |
Ben Murdoch | 4a90d5f | 2016-03-22 12:00:34 +0000 | [diff] [blame] | 127 | } // namespace base |
| 128 | } // namespace v8 |
Ben Murdoch | b8a8cc1 | 2014-11-26 15:28:44 +0000 | [diff] [blame] | 129 | |
| 130 | #endif // V8_BASE_UTILS_RANDOM_NUMBER_GENERATOR_H_ |