lib/Support/RandomNumberGenerator.cpp

//===-- 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.
//
//===----------------------------------------------------------------------===//

#include "llvm/Support/RandomNumberGenerator.h"
#include "llvm/Support/CommandLine.h"
#include "llvm/Support/Debug.h"
#include "llvm/Support/raw_ostream.h"
#ifdef LLVM_ON_WIN32
#include "Windows/WindowsSupport.h"
#else
#include "Unix/Unix.h"
#endif

using namespace llvm;

#define DEBUG_TYPE "rng"

// 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.resize(2 + Salt.size());
  Data[0] = Seed;
  Data[1] = Seed >> 32;

  std::copy(Salt.begin(), Salt.end(), Data.begin() + 2);

  std::seed_seq SeedSeq(Data.begin(), Data.end());
  Generator.seed(SeedSeq);
}

RandomNumberGenerator::result_type RandomNumberGenerator::operator()() {
  return Generator();
}

// Get random vector of specified size
std::error_code llvm::getRandomBytes(void *Buffer, size_t Size) {
#ifdef LLVM_ON_WIN32
  HCRYPTPROV hProvider;
  if (CryptAcquireContext(&hProvider, 0, 0, PROV_RSA_FULL,
                           CRYPT_VERIFYCONTEXT | CRYPT_SILENT)) {
    ScopedCryptContext ScopedHandle(hProvider);
    if (CryptGenRandom(hProvider, Size, static_cast<BYTE *>(Buffer)))
      return std::error_code();
  }
  return std::error_code(GetLastError(), std::system_category());
#else
  int Fd = open("/dev/urandom", O_RDONLY);
  if (Fd != -1) {
    std::error_code Ret;
    ssize_t BytesRead = read(Fd, Buffer, Size);
    if (BytesRead == -1)
      Ret = std::error_code(errno, std::system_category());
    else if (BytesRead != static_cast<ssize_t>(Size))
      Ret = std::error_code(EIO, std::system_category());
    if (close(Fd) == -1)
      Ret = std::error_code(errno, std::system_category());

    return Ret;
  }
  return std::error_code(errno, std::system_category());
#endif
}