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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 deterministic random number
11 // generation (RNG).  Note that the current implementation is not
12 // cryptographically secure 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/Support/Compiler.h"
20 #include "llvm/Support/DataTypes.h" // Needed for uint64_t on Windows.
21 #include <random>
22 
23 namespace llvm {
24 class StringRef;
25 
26 /// A random number generator.
27 ///
28 /// Instances of this class should not be shared across threads. The
29 /// seed should be set by passing the -rng-seed=<uint64> option. Use
30 /// Module::createRNG to create a new RNG instance for use with that
31 /// module.
32 class RandomNumberGenerator {
33 public:
34   /// Returns a random number in the range [0, Max).
35   uint_fast64_t operator()();
36 
37 private:
38   /// Seeds and salts the underlying RNG engine.
39   ///
40   /// This constructor should not be used directly. Instead use
41   /// Module::createRNG to create a new RNG salted with the Module ID.
42   RandomNumberGenerator(StringRef Salt);
43 
44   // 64-bit Mersenne Twister by Matsumoto and Nishimura, 2000
45   // http://en.cppreference.com/w/cpp/numeric/random/mersenne_twister_engine
46   // This RNG is deterministically portable across C++11
47   // implementations.
48   std::mt19937_64 Generator;
49 
50   // Noncopyable.
51   RandomNumberGenerator(const RandomNumberGenerator &other) = delete;
52   RandomNumberGenerator &operator=(const RandomNumberGenerator &other) = delete;
53 
54   friend class Module;
55 };
56 }
57 
58 #endif
59