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//==- llvm/Support/RandomNumberGenerator.h - RNG for diversity ---*- C++ -*-==//
//
// The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
//
// This file defines an abstraction for random number generation (RNG).
// Note that the current implementation is not cryptographically secure
// as it uses the C++11 <random> facilities.
//
//===----------------------------------------------------------------------===//
#ifndef LLVM_SUPPORT_RANDOMNUMBERGENERATOR_H_
#define LLVM_SUPPORT_RANDOMNUMBERGENERATOR_H_
#include "llvm/ADT/StringRef.h"
#include "llvm/Support/DataTypes.h" // Needed for uint64_t on Windows.
#include <random>
namespace llvm {
/// A random number generator.
/// Instances of this class should not be shared across threads.
class RandomNumberGenerator {
public:
/// Seeds and salts the underlying RNG engine. The salt of type StringRef
/// is passed into the constructor. The seed can be set on the command
/// line via -rng-seed=<uint64>.
/// The reason for the salt is to ensure different random streams even if
/// the same seed is used for multiple invocations of the compiler.
/// A good salt value should add additional entropy and be constant across
/// different machines (i.e., no paths) to allow for reproducible builds.
/// An instance of this class can be retrieved from the current Module.
/// \see Module::getRNG
RandomNumberGenerator(StringRef Salt);
/// Returns a random number in the range [0, Max).
uint64_t next(uint64_t Max);
private:
// 64-bit Mersenne Twister by Matsumoto and Nishimura, 2000
// http://en.cppreference.com/w/cpp/numeric/random/mersenne_twister_engine
std::mt19937_64 Generator;
// Noncopyable.
RandomNumberGenerator(const RandomNumberGenerator &other) = delete;
RandomNumberGenerator &operator=(const RandomNumberGenerator &other) = delete;
};
}
#endif
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