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Diffstat (limited to 'boost/random/independent_bits.hpp')
| -rw-r--r-- | boost/random/independent_bits.hpp | 260 |
1 files changed, 260 insertions, 0 deletions
diff --git a/boost/random/independent_bits.hpp b/boost/random/independent_bits.hpp new file mode 100644 index 0000000000..f387fe2d8f --- /dev/null +++ b/boost/random/independent_bits.hpp @@ -0,0 +1,260 @@ +/* boost random/independent_bits.hpp header file + * + * Copyright Steven Watanabe 2011 + * 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) + * + * See http://www.boost.org for most recent version including documentation. + * + * $Id: independent_bits.hpp 71018 2011-04-05 21:27:52Z steven_watanabe $ + * + */ + +#ifndef BOOST_RANDOM_INDEPENDENT_BITS_HPP +#define BOOST_RANDOM_INDEPENDENT_BITS_HPP + +#include <istream> +#include <iosfwd> +#include <boost/assert.hpp> +#include <boost/limits.hpp> +#include <boost/config.hpp> +#include <boost/cstdint.hpp> +#include <boost/integer/integer_mask.hpp> +#include <boost/type_traits/make_unsigned.hpp> +#include <boost/random/detail/config.hpp> +#include <boost/random/detail/integer_log2.hpp> +#include <boost/random/detail/operators.hpp> +#include <boost/random/detail/seed.hpp> +#include <boost/random/detail/seed_impl.hpp> +#include <boost/random/detail/signed_unsigned_tools.hpp> + +namespace boost { +namespace random { + +/** + * An instantiation of class template @c independent_bits_engine + * model a \pseudo_random_number_generator. It generates random + * numbers distributed between [0, 2^w) by combining one or + * more invocations of the base engine. + * + * Requires: 0 < w <= std::numeric_limits<UIntType>::digits + */ +template<class Engine, std::size_t w, class UIntType> +class independent_bits_engine +{ +public: + typedef Engine base_type; + typedef UIntType result_type; + + // Required by old Boost.Random concept + BOOST_STATIC_CONSTANT(bool, has_fixed_range = false); + + /** Returns the smallest value that the generator can produce. */ + static result_type min BOOST_PREVENT_MACRO_SUBSTITUTION () + { return 0; } + /** Returns the largest value that the generator can produce. */ + static result_type max BOOST_PREVENT_MACRO_SUBSTITUTION () + { return boost::low_bits_mask_t<w>::sig_bits; } + + /** + * Constructs an @c independent_bits_engine using the + * default constructor of the base generator. + */ + independent_bits_engine() { } + + /** + * Constructs an @c independent_bits_engine, using seed as + * the constructor argument for both base generators. + */ + BOOST_RANDOM_DETAIL_ARITHMETIC_CONSTRUCTOR(independent_bits_engine, + result_type, seed_arg) + { + _base.seed(seed_arg); + } + + /** + * Constructs an @c independent_bits_engine, using seq as + * the constructor argument for the base generator. + */ + BOOST_RANDOM_DETAIL_SEED_SEQ_CONSTRUCTOR(independent_bits_engine, + SeedSeq, seq) + { _base.seed(seq); } + + /** Constructs an @c independent_bits_engine by copying @c base. */ + independent_bits_engine(const base_type& base_arg) : _base(base_arg) {} + + /** + * Contructs an @c independent_bits_engine with + * values from the range defined by the input iterators first + * and last. first will be modified to point to the element + * after the last one used. + * + * Throws: @c std::invalid_argument if the input range is too small. + * + * Exception Safety: Basic + */ + template<class It> + independent_bits_engine(It& first, It last) : _base(first, last) { } + + /** + * Seeds an @c independent_bits_engine using the default + * seed of the base generator. + */ + void seed() { _base.seed(); } + + /** + * Seeds an @c independent_bits_engine, using @c seed as the + * seed for the base generator. + */ + BOOST_RANDOM_DETAIL_ARITHMETIC_SEED(independent_bits_engine, + result_type, seed_arg) + { _base.seed(seed_arg); } + + /** + * Seeds an @c independent_bits_engine, using @c seq to + * seed the base generator. + */ + BOOST_RANDOM_DETAIL_SEED_SEQ_SEED(independent_bits_engine, + SeedSeq, seq) + { _base.seed(seq); } + + /** + * Seeds an @c independent_bits_engine with + * values from the range defined by the input iterators first + * and last. first will be modified to point to the element + * after the last one used. + * + * Throws: @c std::invalid_argument if the input range is too small. + * + * Exception Safety: Basic + */ + template<class It> void seed(It& first, It last) + { _base.seed(first, last); } + + /** Returns the next value of the generator. */ + result_type operator()() + { + // While it may seem wasteful to recalculate this + // every time, both msvc and gcc can propagate + // constants, resolving this at compile time. + base_unsigned range = + detail::subtract<base_result>()((_base.max)(), (_base.min)()); + std::size_t m = + (range == (std::numeric_limits<base_unsigned>::max)()) ? + std::numeric_limits<base_unsigned>::digits : + detail::integer_log2(range + 1); + std::size_t n = (w + m - 1) / m; + std::size_t w0, n0; + base_unsigned y0, y1; + base_unsigned y0_mask, y1_mask; + calc_params(n, range, w0, n0, y0, y1, y0_mask, y1_mask); + if(base_unsigned(range - y0 + 1) > y0 / n) { + // increment n and try again. + ++n; + calc_params(n, range, w0, n0, y0, y1, y0_mask, y1_mask); + } + + BOOST_ASSERT(n0*w0 + (n - n0)*(w0 + 1) == w); + + result_type S = 0; + for(std::size_t k = 0; k < n0; ++k) { + base_unsigned u; + do { + u = detail::subtract<base_result>()(_base(), (_base.min)()); + } while(u > base_unsigned(y0 - 1)); + S = (S << w0) + (u & y0_mask); + } + for(std::size_t k = 0; k < (n - n0); ++k) { + base_unsigned u; + do { + u = detail::subtract<base_result>()(_base(), (_base.min)()); + } while(u > base_unsigned(y1 - 1)); + S = (S << (w0 + 1)) + (u & y1_mask); + } + return S; + } + + /** Fills a range with random values */ + template<class Iter> + void generate(Iter first, Iter last) + { detail::generate_from_int(*this, first, last); } + + /** Advances the state of the generator by @c z. */ + void discard(boost::uintmax_t z) + { + for(boost::uintmax_t i = 0; i < z; ++i) { + (*this)(); + } + } + + const base_type& base() const { return _base; } + + /** + * Writes the textual representation if the generator to a @c std::ostream. + * The textual representation of the engine is the textual representation + * of the base engine. + */ + BOOST_RANDOM_DETAIL_OSTREAM_OPERATOR(os, independent_bits_engine, r) + { + os << r._base; + return os; + } + + /** + * Reads the state of an @c independent_bits_engine from a + * @c std::istream. + */ + BOOST_RANDOM_DETAIL_ISTREAM_OPERATOR(is, independent_bits_engine, r) + { + is >> r._base; + return is; + } + + /** + * Returns: true iff the two @c independent_bits_engines will + * produce the same sequence of values. + */ + BOOST_RANDOM_DETAIL_EQUALITY_OPERATOR(independent_bits_engine, x, y) + { return x._base == y._base; } + /** + * Returns: true iff the two @c independent_bits_engines will + * produce different sequences of values. + */ + BOOST_RANDOM_DETAIL_INEQUALITY_OPERATOR(independent_bits_engine) + +private: + + /// \cond show_private + typedef typename base_type::result_type base_result; + typedef typename make_unsigned<base_result>::type base_unsigned; + + void calc_params( + std::size_t n, base_unsigned range, + std::size_t& w0, std::size_t& n0, + base_unsigned& y0, base_unsigned& y1, + base_unsigned& y0_mask, base_unsigned& y1_mask) + { + BOOST_ASSERT(w >= n); + w0 = w/n; + n0 = n - w % n; + y0_mask = (base_unsigned(2) << (w0 - 1)) - 1; + y1_mask = (y0_mask << 1) | 1; + y0 = (range + 1) & ~y0_mask; + y1 = (range + 1) & ~y1_mask; + BOOST_ASSERT(y0 != 0 || base_unsigned(range + 1) == 0); + } + /// \endcond + + Engine _base; +}; + +#ifndef BOOST_NO_INCLASS_MEMBER_INITIALIZATION +template<class Engine, std::size_t w, class UIntType> +const bool independent_bits_engine<Engine, w, UIntType>::has_fixed_range; +#endif + +} // namespace random +} // namespace boost + +#endif // BOOST_RANDOM_INDEPENDENT_BITS_HPP |