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//===-- RandomNumberGenerator.cpp - Implement RNG class -------------------===//
//
// The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
//
// This file implements deterministic random number generation (RNG).
// The current implementation is NOT cryptographically secure as it uses
// the C++11 <random> facilities.
//
//===----------------------------------------------------------------------===//
#define DEBUG_TYPE "rng"
#include "llvm/Support/CommandLine.h"
#include "llvm/Support/Debug.h"
#include "llvm/Support/RandomNumberGenerator.h"
using namespace llvm;
// Tracking BUG: 19665
// http://llvm.org/bugs/show_bug.cgi?id=19665
//
// Do not change to cl::opt<uint64_t> since this silently breaks argument parsing.
static cl::opt<unsigned long long>
Seed("rng-seed", cl::value_desc("seed"),
cl::desc("Seed for the random number generator"), cl::init(0));
RandomNumberGenerator::RandomNumberGenerator(StringRef Salt) {
DEBUG(
if (Seed == 0)
dbgs() << "Warning! Using unseeded random number generator.\n"
);
// Combine seed and salts using std::seed_seq.
// Data: Seed-low, Seed-high, Salt
// Note: std::seed_seq can only store 32-bit values, even though we
// are using a 64-bit RNG. This isn't a problem since the Mersenne
// twister constructor copies these correctly into its initial state.
std::vector<uint32_t> Data;
Data.reserve(2 + Salt.size());
Data.push_back(Seed);
Data.push_back(Seed >> 32);
std::copy(Salt.begin(), Salt.end(), Data.end());
std::seed_seq SeedSeq(Data.begin(), Data.end());
Generator.seed(SeedSeq);
}
uint_fast64_t RandomNumberGenerator::operator()() {
return Generator();
}
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