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main_repo / deps / v8 / src / utils / random-number-generator.h @ f230a1cf
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// Copyright 2013 the V8 project authors. All rights reserved.
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// Redistribution and use in source and binary forms, with or without
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// modification, are permitted provided that the following conditions are
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// met:
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//
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// * Redistributions of source code must retain the above copyright
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// notice, this list of conditions and the following disclaimer.
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// * Redistributions in binary form must reproduce the above
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// copyright notice, this list of conditions and the following
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// disclaimer in the documentation and/or other materials provided
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// with the distribution.
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// * Neither the name of Google Inc. nor the names of its
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// contributors may be used to endorse or promote products derived
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// from this software without specific prior written permission.
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//
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// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
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// "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
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// LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
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// A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
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// OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
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// SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
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// LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
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// DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
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// THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
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// (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
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// OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
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#ifndef V8_UTILS_RANDOM_NUMBER_GENERATOR_H_
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#define V8_UTILS_RANDOM_NUMBER_GENERATOR_H_
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#include "globals.h" |
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namespace v8 { |
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namespace internal { |
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// -----------------------------------------------------------------------------
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// RandomNumberGenerator
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//
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// This class is used to generate a stream of pseudorandom numbers. The class
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// uses a 48-bit seed, which is modified using a linear congruential formula.
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// (See Donald Knuth, The Art of Computer Programming, Volume 3, Section 3.2.1.)
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// If two instances of RandomNumberGenerator are created with the same seed, and
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// the same sequence of method calls is made for each, they will generate and
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// return identical sequences of numbers.
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// This class uses (probably) weak entropy by default, but it's sufficient,
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// because it is the responsibility of the embedder to install an entropy source
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// using v8::V8::SetEntropySource(), which provides reasonable entropy, see:
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// https://code.google.com/p/v8/issues/detail?id=2905
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// This class is neither reentrant nor threadsafe.
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class RandomNumberGenerator V8_FINAL { |
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public:
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// EntropySource is used as a callback function when V8 needs a source of
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// entropy.
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typedef bool (*EntropySource)(unsigned char* buffer, size_t buflen); |
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static void SetEntropySource(EntropySource entropy_source); |
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RandomNumberGenerator(); |
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explicit RandomNumberGenerator(int64_t seed) { SetSeed(seed); } |
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// Returns the next pseudorandom, uniformly distributed int value from this
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// random number generator's sequence. The general contract of |NextInt()| is
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// that one int value is pseudorandomly generated and returned.
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// All 2^32 possible integer values are produced with (approximately) equal
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// probability.
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V8_INLINE int NextInt() V8_WARN_UNUSED_RESULT {
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return Next(32); |
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} |
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// Returns a pseudorandom, uniformly distributed int value between 0
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// (inclusive) and the specified max value (exclusive), drawn from this random
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// number generator's sequence. The general contract of |NextInt(int)| is that
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// one int value in the specified range is pseudorandomly generated and
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// returned. All max possible int values are produced with (approximately)
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// equal probability.
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int NextInt(int max) V8_WARN_UNUSED_RESULT; |
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// Returns the next pseudorandom, uniformly distributed boolean value from
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// this random number generator's sequence. The general contract of
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// |NextBoolean()| is that one boolean value is pseudorandomly generated and
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// returned. The values true and false are produced with (approximately) equal
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// probability.
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V8_INLINE bool NextBool() V8_WARN_UNUSED_RESULT {
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return Next(1) != 0; |
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} |
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// Returns the next pseudorandom, uniformly distributed double value between
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// 0.0 and 1.0 from this random number generator's sequence.
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// The general contract of |NextDouble()| is that one double value, chosen
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// (approximately) uniformly from the range 0.0 (inclusive) to 1.0
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// (exclusive), is pseudorandomly generated and returned.
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double NextDouble() V8_WARN_UNUSED_RESULT;
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// Fills the elements of a specified array of bytes with random numbers.
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void NextBytes(void* buffer, size_t buflen); |
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private:
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static const int64_t kMultiplier = V8_2PART_UINT64_C(0x5, deece66d); |
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static const int64_t kAddend = 0xb; |
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static const int64_t kMask = V8_2PART_UINT64_C(0xffff, ffffffff); |
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int Next(int bits) V8_WARN_UNUSED_RESULT; |
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void SetSeed(int64_t seed);
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int64_t seed_; |
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}; |
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} } // namespace v8::internal
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#endif // V8_UTILS_RANDOM_NUMBER_GENERATOR_H_ |