+/* 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
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