1//==- llvm/Support/RandomNumberGenerator.h - RNG for diversity ---*- C++ -*-==//
2//
3//                     The LLVM Compiler Infrastructure
4//
5// This file is distributed under the University of Illinois Open Source
6// License. See LICENSE.TXT for details.
7//
8//===----------------------------------------------------------------------===//
9//
10// This file defines an abstraction for random number generation (RNG).
11// Note that the current implementation is not cryptographically secure
12// as it uses the C++11 <random> facilities.
13//
14//===----------------------------------------------------------------------===//
15
16#ifndef LLVM_SUPPORT_RANDOMNUMBERGENERATOR_H_
17#define LLVM_SUPPORT_RANDOMNUMBERGENERATOR_H_
18
19#include "llvm/ADT/StringRef.h"
20#include "llvm/Support/Compiler.h"
21#include "llvm/Support/DataTypes.h" // Needed for uint64_t on Windows.
22#include <random>
23
24namespace llvm {
25
26/// A random number generator.
27/// Instances of this class should not be shared across threads.
28class RandomNumberGenerator {
29public:
30  /// Seeds and salts the underlying RNG engine. The salt of type StringRef
31  /// is passed into the constructor. The seed can be set on the command
32  /// line via -rng-seed=<uint64>.
33  /// The reason for the salt is to ensure different random streams even if
34  /// the same seed is used for multiple invocations of the compiler.
35  /// A good salt value should add additional entropy and be constant across
36  /// different machines (i.e., no paths) to allow for reproducible builds.
37  /// An instance of this class can be retrieved from the current Module.
38  /// \see Module::getRNG
39  RandomNumberGenerator(StringRef Salt);
40
41  /// Returns a random number in the range [0, Max).
42  uint64_t next(uint64_t Max);
43
44private:
45  // 64-bit Mersenne Twister by Matsumoto and Nishimura, 2000
46  // http://en.cppreference.com/w/cpp/numeric/random/mersenne_twister_engine
47  std::mt19937_64 Generator;
48
49  // Noncopyable.
50  RandomNumberGenerator(const RandomNumberGenerator &other)
51      LLVM_DELETED_FUNCTION;
52  RandomNumberGenerator &
53  operator=(const RandomNumberGenerator &other) LLVM_DELETED_FUNCTION;
54};
55}
56
57#endif
58