Random Number Generator (llvm)

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

URL: http://reviews.llvm.org/D3390
Author: yln

I'm landing this for the second time, it broke Windows bots the first time around.

llvm-svn: 211705

1 files changed, 61 insertions, 0 deletions

diff --git a/llvm/lib/Support/RandomNumberGenerator.cpp b/llvm/lib/Support/RandomNumberGenerator.cpp
new file mode 100644
index 00000000000..c50e7cb8fbe
--- /dev/null
+++ b/llvm/lib/Support/RandomNumberGenerator.cpp
@@ -0,0 +1,61 @@
+//===-- RandomNumberGenerator.cpp - Implement RNG class -------------------===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+//
+// This file implements random number generation (RNG).
+// The current implementation is NOT cryptographically secure as it uses
+// the C++11 <random> facilities.
+//
+//===----------------------------------------------------------------------===//
+
+#define DEBUG_TYPE "rng"
+#include "llvm/Support/RandomNumberGenerator.h"
+#include "llvm/Support/CommandLine.h"
+#include "llvm/Support/Debug.h"
+
+using namespace llvm;
+
+// Tracking BUG: 19665
+// http://llvm.org/bugs/show_bug.cgi?id=19665
+//
+// Do not change to cl::opt<uint64_t> since this silently breaks argument parsing.
+static cl::opt<unsigned long long>
+Seed("rng-seed", cl::value_desc("seed"),
+     cl::desc("Seed for the random number generator"), cl::init(0));
+
+RandomNumberGenerator::RandomNumberGenerator(StringRef Salt) {
+  DEBUG(
+    if (Seed == 0)
+      errs() << "Warning! Using unseeded random number generator.\n"
+  );
+
+  // Combine seed and salt using std::seed_seq.
+  // Entropy: Seed-low, Seed-high, Salt...
+  std::vector<uint32_t> Data;
+  Data.reserve(2 + Salt.size()/4 + 1);
+  Data.push_back(Seed);
+  Data.push_back(Seed >> 32);
+
+  uint32_t Pack = 0;
+  for (size_t I = 0; I < Salt.size(); ++I) {
+    Pack <<= 8;
+    Pack += Salt[I];
+
+    if (I%4 == 3)
+      Data.push_back(Pack);
+  }
+  Data.push_back(Pack);
+
+  std::seed_seq SeedSeq(Data.begin(), Data.end());
+  Generator.seed(SeedSeq);
+}
+
+uint64_t RandomNumberGenerator::next(uint64_t Max) {
+  std::uniform_int_distribution<uint64_t> distribution(0, Max - 1);
+  return distribution(Generator);
+}