1//===-- RandomNumberGenerator.cpp - Implement RNG class -------------------===//
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 implements deterministic random number generation (RNG).
11// The current implementation is NOT cryptographically secure as it uses
12// the C++11 <random> facilities.
13//
14//===----------------------------------------------------------------------===//
15
16#include "llvm/Support/RandomNumberGenerator.h"
17#include "llvm/Support/CommandLine.h"
18#include "llvm/Support/Debug.h"
19#include "llvm/Support/raw_ostream.h"
20
21using namespace llvm;
22
23#define DEBUG_TYPE "rng"
24
25// Tracking BUG: 19665
26// http://llvm.org/bugs/show_bug.cgi?id=19665
27//
28// Do not change to cl::opt<uint64_t> since this silently breaks argument parsing.
29static cl::opt<unsigned long long>
30Seed("rng-seed", cl::value_desc("seed"),
31     cl::desc("Seed for the random number generator"), cl::init(0));
32
33RandomNumberGenerator::RandomNumberGenerator(StringRef Salt) {
34  DEBUG(
35    if (Seed == 0)
36      dbgs() << "Warning! Using unseeded random number generator.\n"
37  );
38
39  // Combine seed and salts using std::seed_seq.
40  // Data: Seed-low, Seed-high, Salt
41  // Note: std::seed_seq can only store 32-bit values, even though we
42  // are using a 64-bit RNG. This isn't a problem since the Mersenne
43  // twister constructor copies these correctly into its initial state.
44  std::vector<uint32_t> Data;
45  Data.reserve(2 + Salt.size());
46  Data.push_back(Seed);
47  Data.push_back(Seed >> 32);
48
49  std::copy(Salt.begin(), Salt.end(), Data.end());
50
51  std::seed_seq SeedSeq(Data.begin(), Data.end());
52  Generator.seed(SeedSeq);
53}
54
55uint_fast64_t RandomNumberGenerator::operator()() {
56  return Generator();
57}
58