1 // Copyright 2013 the V8 project authors. All rights reserved. 2 // Redistribution and use in source and binary forms, with or without 3 // modification, are permitted provided that the following conditions are 4 // met: 5 // 6 // * Redistributions of source code must retain the above copyright 7 // notice, this list of conditions and the following disclaimer. 8 // * Redistributions in binary form must reproduce the above 9 // copyright notice, this list of conditions and the following 10 // disclaimer in the documentation and/or other materials provided 11 // with the distribution. 12 // * Neither the name of Google Inc. nor the names of its 13 // contributors may be used to endorse or promote products derived 14 // from this software without specific prior written permission. 15 // 16 // THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS 17 // "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT 18 // LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR 19 // A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT 20 // OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, 21 // SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT 22 // LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, 23 // DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY 24 // THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT 25 // (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE 26 // OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. 27 28 #ifndef V8_UTILS_RANDOM_NUMBER_GENERATOR_H_ 29 #define V8_UTILS_RANDOM_NUMBER_GENERATOR_H_ 30 31 #include "globals.h" 32 33 namespace v8 { 34 namespace internal { 35 36 // ----------------------------------------------------------------------------- 37 // RandomNumberGenerator 38 // 39 // This class is used to generate a stream of pseudorandom numbers. The class 40 // uses a 48-bit seed, which is modified using a linear congruential formula. 41 // (See Donald Knuth, The Art of Computer Programming, Volume 3, Section 3.2.1.) 42 // If two instances of RandomNumberGenerator are created with the same seed, and 43 // the same sequence of method calls is made for each, they will generate and 44 // return identical sequences of numbers. 45 // This class uses (probably) weak entropy by default, but it's sufficient, 46 // because it is the responsibility of the embedder to install an entropy source 47 // using v8::V8::SetEntropySource(), which provides reasonable entropy, see: 48 // https://code.google.com/p/v8/issues/detail?id=2905 49 // This class is neither reentrant nor threadsafe. 50 51 class RandomNumberGenerator V8_FINAL { 52 public: 53 // EntropySource is used as a callback function when V8 needs a source of 54 // entropy. 55 typedef bool (*EntropySource)(unsigned char* buffer, size_t buflen); 56 static void SetEntropySource(EntropySource entropy_source); 57 58 RandomNumberGenerator(); 59 explicit RandomNumberGenerator(int64_t seed) { SetSeed(seed); } 60 61 // Returns the next pseudorandom, uniformly distributed int value from this 62 // random number generator's sequence. The general contract of |NextInt()| is 63 // that one int value is pseudorandomly generated and returned. 64 // All 2^32 possible integer values are produced with (approximately) equal 65 // probability. 66 V8_INLINE int NextInt() V8_WARN_UNUSED_RESULT { 67 return Next(32); 68 } 69 70 // Returns a pseudorandom, uniformly distributed int value between 0 71 // (inclusive) and the specified max value (exclusive), drawn from this random 72 // number generator's sequence. The general contract of |NextInt(int)| is that 73 // one int value in the specified range is pseudorandomly generated and 74 // returned. All max possible int values are produced with (approximately) 75 // equal probability. 76 int NextInt(int max) V8_WARN_UNUSED_RESULT; 77 78 // Returns the next pseudorandom, uniformly distributed boolean value from 79 // this random number generator's sequence. The general contract of 80 // |NextBoolean()| is that one boolean value is pseudorandomly generated and 81 // returned. The values true and false are produced with (approximately) equal 82 // probability. 83 V8_INLINE bool NextBool() V8_WARN_UNUSED_RESULT { 84 return Next(1) != 0; 85 } 86 87 // Returns the next pseudorandom, uniformly distributed double value between 88 // 0.0 and 1.0 from this random number generator's sequence. 89 // The general contract of |NextDouble()| is that one double value, chosen 90 // (approximately) uniformly from the range 0.0 (inclusive) to 1.0 91 // (exclusive), is pseudorandomly generated and returned. 92 double NextDouble() V8_WARN_UNUSED_RESULT; 93 94 // Fills the elements of a specified array of bytes with random numbers. 95 void NextBytes(void* buffer, size_t buflen); 96 97 private: 98 static const int64_t kMultiplier = V8_2PART_UINT64_C(0x5, deece66d); 99 static const int64_t kAddend = 0xb; 100 static const int64_t kMask = V8_2PART_UINT64_C(0xffff, ffffffff); 101 102 int Next(int bits) V8_WARN_UNUSED_RESULT; 103 void SetSeed(int64_t seed); 104 105 int64_t seed_; 106 }; 107 108 } } // namespace v8::internal 109 110 #endif // V8_UTILS_RANDOM_NUMBER_GENERATOR_H_ 111
