272 lines
8.8 KiB
Plaintext
272 lines
8.8 KiB
Plaintext
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/* boost random/independent_bits.hpp header file
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*
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* Copyright Steven Watanabe 2011
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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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* See http://www.boost.org for most recent version including documentation.
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*
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* $Id$
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*
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*/
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#ifndef BOOST_RANDOM_INDEPENDENT_BITS_HPP
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#define BOOST_RANDOM_INDEPENDENT_BITS_HPP
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#include <istream>
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#include <iosfwd>
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#include <boost/assert.hpp>
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#include <boost/limits.hpp>
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#include <boost/config.hpp>
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#include <boost/cstdint.hpp>
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#include <boost/integer/integer_mask.hpp>
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#include <boost/random/traits.hpp>
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#include <boost/random/detail/config.hpp>
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#include <boost/random/detail/integer_log2.hpp>
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#include <boost/random/detail/operators.hpp>
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#include <boost/random/detail/seed.hpp>
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#include <boost/random/detail/seed_impl.hpp>
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#include <boost/random/detail/signed_unsigned_tools.hpp>
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namespace boost {
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namespace random {
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/**
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* An instantiation of class template @c independent_bits_engine
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* model a \pseudo_random_number_generator. It generates random
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* numbers distributed between [0, 2^w) by combining one or
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* more invocations of the base engine.
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*
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* Requires: 0 < w <= std::numeric_limits<UIntType>::digits
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*/
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template<class Engine, std::size_t w, class UIntType>
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class independent_bits_engine
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{
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public:
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typedef Engine base_type;
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typedef UIntType result_type;
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typedef typename Engine::result_type base_result_type;
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// Required by old Boost.Random concept
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BOOST_STATIC_CONSTANT(bool, has_fixed_range = false);
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/** Returns the smallest value that the generator can produce. */
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static result_type min BOOST_PREVENT_MACRO_SUBSTITUTION ()
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{ return 0; }
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/** Returns the largest value that the generator can produce. */
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static result_type max BOOST_PREVENT_MACRO_SUBSTITUTION ()
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{ return max_imp(boost::is_integral<UIntType>()); }
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/**
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* Constructs an @c independent_bits_engine using the
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* default constructor of the base generator.
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*/
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independent_bits_engine() { }
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/**
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* Constructs an @c independent_bits_engine, using seed as
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* the constructor argument for both base generators.
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*/
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BOOST_RANDOM_DETAIL_ARITHMETIC_CONSTRUCTOR(independent_bits_engine,
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base_result_type, seed_arg)
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{
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_base.seed(seed_arg);
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}
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/**
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* Constructs an @c independent_bits_engine, using seq as
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* the constructor argument for the base generator.
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*/
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BOOST_RANDOM_DETAIL_SEED_SEQ_CONSTRUCTOR(independent_bits_engine,
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SeedSeq, seq)
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{ _base.seed(seq); }
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/** Constructs an @c independent_bits_engine by copying @c base. */
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independent_bits_engine(const base_type& base_arg) : _base(base_arg) {}
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/**
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* Contructs an @c independent_bits_engine with
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* values from the range defined by the input iterators first
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* and last. first will be modified to point to the element
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* after the last one used.
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*
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* Throws: @c std::invalid_argument if the input range is too small.
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*
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* Exception Safety: Basic
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*/
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template<class It>
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independent_bits_engine(It& first, It last) : _base(first, last) { }
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/**
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* Seeds an @c independent_bits_engine using the default
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* seed of the base generator.
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*/
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void seed() { _base.seed(); }
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/**
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* Seeds an @c independent_bits_engine, using @c seed as the
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* seed for the base generator.
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*/
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BOOST_RANDOM_DETAIL_ARITHMETIC_SEED(independent_bits_engine,
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base_result_type, seed_arg)
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{ _base.seed(seed_arg); }
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/**
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* Seeds an @c independent_bits_engine, using @c seq to
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* seed the base generator.
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*/
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BOOST_RANDOM_DETAIL_SEED_SEQ_SEED(independent_bits_engine,
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SeedSeq, seq)
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{ _base.seed(seq); }
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/**
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* Seeds an @c independent_bits_engine with
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* values from the range defined by the input iterators first
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* and last. first will be modified to point to the element
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* after the last one used.
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*
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* Throws: @c std::invalid_argument if the input range is too small.
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*
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* Exception Safety: Basic
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*/
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template<class It> void seed(It& first, It last)
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{ _base.seed(first, last); }
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/** Returns the next value of the generator. */
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result_type operator()()
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{
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// While it may seem wasteful to recalculate this
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// every time, both msvc and gcc can propagate
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// constants, resolving this at compile time.
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base_unsigned range =
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detail::subtract<base_result_type>()((_base.max)(), (_base.min)());
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std::size_t m =
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(range == (std::numeric_limits<base_unsigned>::max)()) ?
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std::numeric_limits<base_unsigned>::digits :
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detail::integer_log2(range + 1);
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std::size_t n = (w + m - 1) / m;
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std::size_t w0, n0;
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base_unsigned y0, y1;
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base_unsigned y0_mask, y1_mask;
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calc_params(n, range, w0, n0, y0, y1, y0_mask, y1_mask);
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if(base_unsigned(range - y0 + 1) > y0 / n) {
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// increment n and try again.
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++n;
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calc_params(n, range, w0, n0, y0, y1, y0_mask, y1_mask);
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}
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BOOST_ASSERT(n0*w0 + (n - n0)*(w0 + 1) == w);
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result_type S = 0;
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for(std::size_t k = 0; k < n0; ++k) {
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base_unsigned u;
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do {
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u = detail::subtract<base_result_type>()(_base(), (_base.min)());
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} while(u > base_unsigned(y0 - 1));
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S = (S << w0) + (u & y0_mask);
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}
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for(std::size_t k = 0; k < (n - n0); ++k) {
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base_unsigned u;
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do {
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u = detail::subtract<base_result_type>()(_base(), (_base.min)());
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} while(u > base_unsigned(y1 - 1));
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S = (S << (w0 + 1)) + (u & y1_mask);
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}
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return S;
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}
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/** Fills a range with random values */
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template<class Iter>
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void generate(Iter first, Iter last)
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{ detail::generate_from_int(*this, first, last); }
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/** Advances the state of the generator by @c z. */
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void discard(boost::uintmax_t z)
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{
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for(boost::uintmax_t i = 0; i < z; ++i) {
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(*this)();
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}
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}
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const base_type& base() const { return _base; }
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/**
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* Writes the textual representation if the generator to a @c std::ostream.
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* The textual representation of the engine is the textual representation
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* of the base engine.
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*/
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BOOST_RANDOM_DETAIL_OSTREAM_OPERATOR(os, independent_bits_engine, r)
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{
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os << r._base;
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return os;
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}
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/**
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* Reads the state of an @c independent_bits_engine from a
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* @c std::istream.
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*/
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BOOST_RANDOM_DETAIL_ISTREAM_OPERATOR(is, independent_bits_engine, r)
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{
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is >> r._base;
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return is;
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}
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/**
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* Returns: true iff the two @c independent_bits_engines will
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* produce the same sequence of values.
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*/
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BOOST_RANDOM_DETAIL_EQUALITY_OPERATOR(independent_bits_engine, x, y)
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{ return x._base == y._base; }
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/**
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* Returns: true iff the two @c independent_bits_engines will
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* produce different sequences of values.
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*/
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BOOST_RANDOM_DETAIL_INEQUALITY_OPERATOR(independent_bits_engine)
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private:
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/// \cond show_private
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typedef typename boost::random::traits::make_unsigned<base_result_type>::type base_unsigned;
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static UIntType max_imp(const boost::true_type&)
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{
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return boost::low_bits_mask_t<w>::sig_bits;
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}
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static UIntType max_imp(const boost::false_type&)
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{
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// We have a multiprecision integer type:
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BOOST_STATIC_ASSERT(std::numeric_limits<UIntType>::is_specialized);
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return w < std::numeric_limits<UIntType>::digits ? UIntType((UIntType(1) << w) - 1) : UIntType((((UIntType(1) << (w - 1)) - 1) << 1) | 1u);
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}
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void calc_params(
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std::size_t n, base_unsigned range,
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std::size_t& w0, std::size_t& n0,
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base_unsigned& y0, base_unsigned& y1,
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base_unsigned& y0_mask, base_unsigned& y1_mask)
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{
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BOOST_ASSERT(w >= n);
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w0 = w/n;
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n0 = n - w % n;
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y0_mask = (base_unsigned(2) << (w0 - 1)) - 1;
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y1_mask = (y0_mask << 1) | 1;
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y0 = (range + 1) & ~y0_mask;
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y1 = (range + 1) & ~y1_mask;
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BOOST_ASSERT(y0 != 0 || base_unsigned(range + 1) == 0);
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}
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/// \endcond
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Engine _base;
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};
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#ifndef BOOST_NO_INCLASS_MEMBER_INITIALIZATION
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template<class Engine, std::size_t w, class UIntType>
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const bool independent_bits_engine<Engine, w, UIntType>::has_fixed_range;
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#endif
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} // namespace random
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} // namespace boost
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#endif // BOOST_RANDOM_INDEPENDENT_BITS_HPP
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