Random Number Generator (llvm)

Summary:
Provides an abstraction for a random number generator (RNG) that produces a stream of pseudo-random numbers.
The current implementation uses C++11 facilities and is therefore not cryptographically secure.

The RNG is salted with the text of the current command line invocation.
In addition, a user may specify a seed (reproducible builds).

In clang, the seed can be set via
  -frandom-seed=X
In the back end, the seed can be set via
  -rng-seed=X

This is the llvm part of the patch.
clang part: D3391

Reviewers: ahomescu, rinon, nicholas, jfb

Reviewed By: jfb

Subscribers: jfb, perl

Differential Revision: http://reviews.llvm.org/D3390

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@211145 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 53 insertions, 0 deletions

diff --git a/include/llvm/Support/RandomNumberGenerator.h b/include/llvm/Support/RandomNumberGenerator.h
new file mode 100644
index 0000000000..84fcdcbc76
--- /dev/null
+++ b/include/llvm/Support/RandomNumberGenerator.h
@@ -0,0 +1,53 @@
+//==- 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 <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