Header <boost/nondet_random.hpp><boost/nondet_random.hpp>
Synopsis
namespace boost {
class random_device;
} // namespace boost
random_device
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()();
};
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 1994for 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.
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.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.
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.
Revised 05 December, 2006
Copyright © 2000-2003 Jens Maurer
Distributed under the Boost Software License, Version 1.0. (See accompanying file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)