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 21 using 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. 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)); 32 33 RandomNumberGenerator::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 55 uint_fast64_t RandomNumberGenerator::operator()() { 56 return Generator(); 57 } 58
