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 random number generation (RNG).
11 // The current implementation is NOT cryptographically secure as it uses
12 // the C++11 <random> facilities.
14 //===----------------------------------------------------------------------===//
16 #define DEBUG_TYPE "rng"
17 #include "llvm/Support/RandomNumberGenerator.h"
18 #include "llvm/Support/CommandLine.h"
19 #include "llvm/Support/Debug.h"
23 // Tracking BUG: 19665
24 // http://llvm.org/bugs/show_bug.cgi?id=19665
26 // Do not change to cl::opt<uint64_t> since this silently breaks argument parsing.
27 static cl::opt<unsigned long long>
28 Seed("rng-seed", cl::value_desc("seed"),
29 cl::desc("Seed for the random number generator"), cl::init(0));
31 RandomNumberGenerator::RandomNumberGenerator(StringRef Salt) {
34 errs() << "Warning! Using unseeded random number generator.\n"
37 // Combine seed and salt using std::seed_seq.
38 // Entropy: Seed-low, Seed-high, Salt...
39 size_t Size = Salt.size() + 2;
43 std::copy_n(Salt.begin(), Salt.size(), Data + 2);
45 std::seed_seq SeedSeq(Data, Data + Size);
46 Generator.seed(SeedSeq);
49 uint64_t RandomNumberGenerator::next(uint64_t Max) {
50 std::uniform_int_distribution<uint64_t> distribution(0, Max - 1);
51 return distribution(Generator);