Class random_device

boost::random_device

Synopsis

// In header: <boost/nondet_random.hpp>


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

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

  // public member functions
  result_type min() const;
  result_type max() const;
  BOOST_RANDOM_DECL double entropy() const;
  BOOST_RANDOM_DECL unsigned int operator()();
  static const bool has_fixed_range;
  static const result_type min_value;
  static const result_type max_value;
};

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 nondet_random.hpp implementation of the above algorithms in a tight loop. The performance has been evaluated on a Pentium Pro 200 MHz with gcc 2.95.2, Linux 2.2.13, glibc 2.1.2.

class	time per invocation [usec]
random_device	92.0

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

`random_device` public construct/copy/destruct

```
random_device(const std::string & token = default_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 member functions

```
result_type min() const;
```
Returns: The smallest value that the random_device can produce.
```
result_type max() const;
```
Returns: The largest value that the random_device can produce.
```
BOOST_RANDOM_DECL 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.

BOOST_RANDOM_DECL unsigned int operator()();

Returns: A random value in the range [min, max]

Boost C++ Libraries