1 //===-- RandomNumberGenerator.cpp - Implement RNG class -------------------===//
3 // The LLVM Compiler Infrastructure
5 // This file is distributed under the University of Illinois Open Source
6 // License. See LICENSE.TXT for details.
8 //===----------------------------------------------------------------------===//
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.
14 //===----------------------------------------------------------------------===//
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"
23 #define DEBUG_TYPE "rng"
25 // Tracking BUG: 19665
26 // http://llvm.org/bugs/show_bug.cgi?id=19665
28 // Do not change to cl::opt<uint64_t> since this silently breaks argument parsing.
29 static cl::opt<unsigned long long>
30 Seed("rng-seed", cl::value_desc("seed"),
31 cl::desc("Seed for the random number generator"), cl::init(0));
33 RandomNumberGenerator::RandomNumberGenerator(StringRef Salt) {
36 dbgs() << "Warning! Using unseeded random number generator.\n"
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());
47 Data.push_back(Seed >> 32);
49 std::copy(Salt.begin(), Salt.end(), Data.end());
51 std::seed_seq SeedSeq(Data.begin(), Data.end());
52 Generator.seed(SeedSeq);
55 uint_fast64_t RandomNumberGenerator::operator()() {