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 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#define DEBUG_TYPE "rng"
17#include "llvm/Support/RandomNumberGenerator.h"
18#include "llvm/Support/CommandLine.h"
19#include "llvm/Support/Debug.h"
20
21using namespace llvm;
22
23// Tracking BUG: 19665
24// http://llvm.org/bugs/show_bug.cgi?id=19665
25//
26// Do not change to cl::opt<uint64_t> since this silently breaks argument parsing.
27static cl::opt<unsigned long long>
28Seed("rng-seed", cl::value_desc("seed"),
29     cl::desc("Seed for the random number generator"), cl::init(0));
30
31RandomNumberGenerator::RandomNumberGenerator(StringRef Salt) {
32  DEBUG(
33    if (Seed == 0)
34      errs() << "Warning! Using unseeded random number generator.\n"
35  );
36
37  // Combine seed and salt using std::seed_seq.
38  // Entropy: Seed-low, Seed-high, Salt...
39  std::vector<uint32_t> Data;
40  Data.reserve(2 + Salt.size()/4 + 1);
41  Data.push_back(Seed);
42  Data.push_back(Seed >> 32);
43
44  uint32_t Pack = 0;
45  for (size_t I = 0; I < Salt.size(); ++I) {
46    Pack <<= 8;
47    Pack += Salt[I];
48
49    if (I%4 == 3)
50      Data.push_back(Pack);
51  }
52  Data.push_back(Pack);
53
54  std::seed_seq SeedSeq(Data.begin(), Data.end());
55  Generator.seed(SeedSeq);
56}
57
58uint64_t RandomNumberGenerator::next(uint64_t Max) {
59  std::uniform_int_distribution<uint64_t> distribution(0, Max - 1);
60  return distribution(Generator);
61}
62