Class random_device

boost::random::random_device

Synopsis

// In header: <boost/random/random_device.hpp>


class random_device : private noncopyable {
public:
  // types
  typedef unsigned int result_type;

  // construct/copy/destruct
  random_device();
  explicit random_device(const std::string &);
  ~random_device();

  // public static functions
  static constexpr result_type min();
  static constexpr result_type max();

  // public member functions
  double entropy() const;
  unsigned int operator()();
  template<typename Iter> void generate(Iter, Iter);

  // public data members
  static const bool has_fixed_range;
};

Description

Class random_device models a non-deterministic random number generator . It uses one or more implementation-defined stochastic processes to generate a sequence of uniformly distributed non-deterministic random numbers. For those environments where a non-deterministic random number generator is not available, class random_device must not be implemented. See

"Randomness Recommendations for Security", D. Eastlake, S. Crocker, J. Schiller, Network Working Group, RFC 1750, December 1994

for further discussions.

	Note
	Some operating systems abstract the computer hardware enough to make it difficult to non-intrusively monitor stochastic processes. However, several do provide a special device for exactly this purpose. It seems to be impossible to emulate the functionality using Standard C++ only, so users should be aware that this class may not be available on all platforms.

Implementation Note for Linux

On the Linux operating system, token is interpreted as a filesystem path. It is assumed that this path denotes an operating system pseudo-device which generates a stream of non-deterministic random numbers. The pseudo-device should never signal an error or end-of-file. Otherwise, std::ios_base::failure is thrown. By default, random_device uses the /dev/urandom pseudo-device to retrieve the random numbers. Another option would be to specify the /dev/random pseudo-device, which blocks on reads if the entropy pool has no more random bits available.

Implementation Note for Windows

On the Windows operating system, token is interpreted as the name of a cryptographic service provider. By default random_device uses MS_DEF_PROV.

Performance

The test program nondet_random_speed.cpp measures the execution times of the random_device.hpp implementation of the above algorithms in a tight loop. The performance has been evaluated on an Intel(R) Core(TM) i7 CPU Q 840 @ 1.87GHz, 1867 Mhz with Visual C++ 2010, Microsoft Windows 7 Professional and with gcc 4.4.5, Ubuntu Linux 2.6.35-25-generic.

Platform	time per invocation [microseconds]
Windows	2.9
Linux	1.7

The measurement error is estimated at +/- 1 usec.

`random_device` public construct/copy/destruct

```
random_device();
```
Constructs a random_device, optionally using the default device.
```
explicit random_device(const std::string & token);
```
Constructs a random_device, optionally using the given token as an access specification (for example, a URL) to some implementation-defined service for monitoring a stochastic process.
```
~random_device();
```

`random_device` public static functions

```
static constexpr result_type min();
```
Returns the smallest value that the random_device can produce.
```
static constexpr result_type max();
```
Returns the largest value that the random_device can produce.

`random_device` public member functions

```
double entropy() const;
```
Returns: An entropy estimate for the random numbers returned by operator(), in the range min() to log2( max()+1). A deterministic random number generator (e.g. a pseudo-random number engine) has entropy 0.

Throws: Nothing.
```
unsigned int operator()();
```
Returns a random value in the range [min, max].

template<typename Iter> void generate(Iter begin, Iter end);

Fills a range with random 32-bit values.

Boost C++ Libraries