| /* 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 |