104 lines
3.3 KiB
Plaintext
104 lines
3.3 KiB
Plaintext
[/
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/ Copyright (c) 2009 Steven Watanabe
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/
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/ Distributed under the Boost Software License, Version 1.0. (See
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/ accompanying file LICENSE_1_0.txt or copy at
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/ http://www.boost.org/LICENSE_1_0.txt)
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]
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[section Header <boost/nondet_random.hpp> Synopsis]
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namespace boost {
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class random_device;
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} // namespace boost
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[endsect]
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[section Class random_device]
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[section Synopsis]
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class random_device : noncopyable
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{
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public:
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typedef unsigned int result_type;
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static const bool has_fixed_range = true;
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static const result_type min_value = /* implementation defined */;
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static const result_type max_value = /* implementation defined */;
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result_type min() const;
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result_type max() const;
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explicit random_device(const std::string& token = default_token);
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~random_device();
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double entropy() const;
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unsigned int operator()();
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};
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[endsect]
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[section Description]
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Class `random_device` models a non-deterministic random number generator. It
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uses one or more implementation-defined stochastic processes to generate a
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sequence of uniformly distributed non-deterministic random numbers. For those
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environments where a non-deterministic random number generator is not
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available, class random_device must not be implemented. See
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[:"Randomness Recommendations for Security", D. Eastlake, S. Crocker,
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J. Schiller, Network Working Group, RFC 1750, December 1994]
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for further discussions.
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[note Some operating systems abstract the computer hardware enough to make it
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difficult to non-intrusively monitor stochastic processes. However, several do
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provide a special device for exactly this purpose. It seems to be impossible
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to emulate the functionality using Standard C++ only, so users should be aware
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that this class may not be available on all platforms.]
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[endsect]
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[section Members]
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explicit random_device(const std::string& token = default_token)
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Effects: Constructs a random_device, optionally using the given token as an
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access specification (for example, a URL) to some implementation-defined
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service for monitoring a stochastic process.
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double entropy() const
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Returns: An entropy estimate for the random numbers returned by `operator()`,
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in the range `min()` to `log2(max()+1)`. A deterministic random number
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generator (e.g. a pseudo-random number engine) has entropy 0.
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Throws: Nothing.
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[endsect]
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Implementation Note for Linux
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On the Linux operating system, token is interpreted as a filesystem path. It
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is assumed that this path denotes an operating system pseudo-device which
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generates a stream of non-deterministic random numbers. The pseudo-device
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should never signal an error or end-of-file. Otherwise, std::ios_base::failure
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is thrown. By default, random_device uses the /dev/urandom pseudo-device to
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retrieve the random numbers. Another option would be to specify the
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/dev/random pseudo-device, which blocks on reads if the entropy pool has no
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more random bits available.
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[endsect]
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[section Performance]
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The test program nondet_random_speed.cpp measures the execution times of the
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nondet_random.hpp implementation of the above algorithms in a tight loop.
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The performance has been evaluated on a Pentium Pro 200 MHz with gcc 2.95.2,
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Linux 2.2.13, glibc 2.1.2.
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[table preformance
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[[class] [time per invocation \[usec\]]]
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[[random_device] [92.0]]
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]
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The measurement error is estimated at +/- 1 usec.
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[endsect]
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