| // Copyright 2013 the V8 project authors. All rights reserved. |
| // Use of this source code is governed by a BSD-style license that can be |
| // found in the LICENSE file. |
| |
| #ifndef V8_BASE_UTILS_RANDOM_NUMBER_GENERATOR_H_ |
| #define V8_BASE_UTILS_RANDOM_NUMBER_GENERATOR_H_ |
| |
| #include "src/base/macros.h" |
| |
| namespace v8 { |
| namespace base { |
| |
| // ----------------------------------------------------------------------------- |
| // RandomNumberGenerator |
| // |
| // This class is used to generate a stream of pseudorandom numbers. The class |
| // uses a 48-bit seed, which is modified using a linear congruential formula. |
| // (See Donald Knuth, The Art of Computer Programming, Volume 3, Section 3.2.1.) |
| // If two instances of RandomNumberGenerator are created with the same seed, and |
| // the same sequence of method calls is made for each, they will generate and |
| // return identical sequences of numbers. |
| // This class uses (probably) weak entropy by default, but it's sufficient, |
| // because it is the responsibility of the embedder to install an entropy source |
| // using v8::V8::SetEntropySource(), which provides reasonable entropy, see: |
| // https://code.google.com/p/v8/issues/detail?id=2905 |
| // This class is neither reentrant nor threadsafe. |
| |
| class RandomNumberGenerator FINAL { |
| public: |
| // EntropySource is used as a callback function when V8 needs a source of |
| // entropy. |
| typedef bool (*EntropySource)(unsigned char* buffer, size_t buflen); |
| static void SetEntropySource(EntropySource entropy_source); |
| |
| RandomNumberGenerator(); |
| explicit RandomNumberGenerator(int64_t seed) { SetSeed(seed); } |
| |
| // Returns the next pseudorandom, uniformly distributed int value from this |
| // random number generator's sequence. The general contract of |NextInt()| is |
| // that one int value is pseudorandomly generated and returned. |
| // All 2^32 possible integer values are produced with (approximately) equal |
| // probability. |
| V8_INLINE int NextInt() WARN_UNUSED_RESULT { |
| return Next(32); |
| } |
| |
| // Returns a pseudorandom, uniformly distributed int value between 0 |
| // (inclusive) and the specified max value (exclusive), drawn from this random |
| // number generator's sequence. The general contract of |NextInt(int)| is that |
| // one int value in the specified range is pseudorandomly generated and |
| // returned. All max possible int values are produced with (approximately) |
| // equal probability. |
| int NextInt(int max) WARN_UNUSED_RESULT; |
| |
| // Returns the next pseudorandom, uniformly distributed boolean value from |
| // this random number generator's sequence. The general contract of |
| // |NextBoolean()| is that one boolean value is pseudorandomly generated and |
| // returned. The values true and false are produced with (approximately) equal |
| // probability. |
| V8_INLINE bool NextBool() WARN_UNUSED_RESULT { |
| return Next(1) != 0; |
| } |
| |
| // Returns the next pseudorandom, uniformly distributed double value between |
| // 0.0 and 1.0 from this random number generator's sequence. |
| // The general contract of |NextDouble()| is that one double value, chosen |
| // (approximately) uniformly from the range 0.0 (inclusive) to 1.0 |
| // (exclusive), is pseudorandomly generated and returned. |
| double NextDouble() WARN_UNUSED_RESULT; |
| |
| // Returns the next pseudorandom, uniformly distributed int64 value from this |
| // random number generator's sequence. The general contract of |NextInt64()| |
| // is that one 64-bit int value is pseudorandomly generated and returned. |
| // All 2^64 possible integer values are produced with (approximately) equal |
| // probability. |
| int64_t NextInt64() WARN_UNUSED_RESULT; |
| |
| // Fills the elements of a specified array of bytes with random numbers. |
| void NextBytes(void* buffer, size_t buflen); |
| |
| // Override the current ssed. |
| void SetSeed(int64_t seed); |
| |
| int64_t initial_seed() const { return initial_seed_; } |
| |
| private: |
| static const int64_t kMultiplier = V8_2PART_UINT64_C(0x5, deece66d); |
| static const int64_t kAddend = 0xb; |
| static const int64_t kMask = V8_2PART_UINT64_C(0xffff, ffffffff); |
| |
| int Next(int bits) WARN_UNUSED_RESULT; |
| |
| int64_t initial_seed_; |
| int64_t seed_; |
| }; |
| |
| } } // namespace v8::base |
| |
| #endif // V8_BASE_UTILS_RANDOM_NUMBER_GENERATOR_H_ |