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c++boost.gif (8819 bytes)Header <boost/nondet_random.hpp>

Header<boost/nondet_random.hpp> Synopsis

namespace boost {
  class random_device;
} // namespace boost

Class random_device

Synopsis

class random_device : noncopyable
{
public:
  typedef unsigned int result_type;
  static const bool has_fixed_range = true;
  static const result_type min_value = /* implementation defined */;
  static const result_type max_value = /* implementation defined */;
  result_type min() const;
  result_type max() const;
  explicit random_device(const std::string& token = default_token);
  ~random_device();
  double entropy() const;
  unsigned int operator()();
};

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.

Members

explicit random_device(const std::string& token = default_token)
Effects: 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.
    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.

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.

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.

classtime per invocation [usec]
random_device92.0

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


Jens Maurer, 2000-06-19