Chris@16: /* boost random/seed_seq.hpp header file
Chris@16:  *
Chris@16:  * Copyright Steven Watanabe 2010
Chris@16:  * Distributed under the Boost Software License, Version 1.0. (See
Chris@16:  * accompanying file LICENSE_1_0.txt or copy at
Chris@16:  * http://www.boost.org/LICENSE_1_0.txt)
Chris@16:  *
Chris@16:  * See http://www.boost.org for most recent version including documentation.
Chris@16:  *
Chris@101:  * $Id$
Chris@16:  *
Chris@16:  */
Chris@16: 
Chris@16: #ifndef BOOST_RANDOM_SEED_SEQ_HPP
Chris@16: #define BOOST_RANDOM_SEED_SEQ_HPP
Chris@16: 
Chris@16: #include <boost/config.hpp>
Chris@16: #include <boost/cstdint.hpp>
Chris@16: #include <boost/range/begin.hpp>
Chris@16: #include <boost/range/end.hpp>
Chris@16: #include <cstddef>
Chris@16: #include <vector>
Chris@16: #include <algorithm>
Chris@16: #include <iterator>
Chris@16: 
Chris@16: #ifndef BOOST_NO_CXX11_HDR_INITIALIZER_LIST
Chris@16: #include <initializer_list>
Chris@16: #endif
Chris@16: 
Chris@16: namespace boost {
Chris@16: namespace random {
Chris@16: 
Chris@16: /**
Chris@16:  * The class @c seed_seq stores a sequence of 32-bit words
Chris@16:  * for seeding a \pseudo_random_number_generator.  These
Chris@16:  * words will be combined to fill the entire state of the
Chris@16:  * generator.
Chris@16:  */
Chris@16: class seed_seq {
Chris@16: public:
Chris@16:     typedef boost::uint_least32_t result_type;
Chris@16: 
Chris@16:     /** Initializes a seed_seq to hold an empty sequence. */
Chris@16:     seed_seq() {}
Chris@16: #ifndef BOOST_NO_CXX11_HDR_INITIALIZER_LIST
Chris@16:     /** Initializes the sequence from an initializer_list. */
Chris@16:     template<class T>
Chris@16:     seed_seq(const std::initializer_list<T>& il) : v(il.begin(), il.end()) {}
Chris@16: #endif
Chris@16:     /** Initializes the sequence from an iterator range. */
Chris@16:     template<class Iter>
Chris@16:     seed_seq(Iter first, Iter last) : v(first, last) {}
Chris@16:     /** Initializes the sequence from Boost.Range range. */
Chris@16:     template<class Range>
Chris@16:     explicit seed_seq(const Range& range)
Chris@16:       : v(boost::begin(range), boost::end(range)) {}
Chris@16: 
Chris@16:     /**
Chris@16:      * Fills a range with 32-bit values based on the stored sequence.
Chris@16:      *
Chris@16:      * Requires: Iter must be a Random Access Iterator whose value type
Chris@16:      * is an unsigned integral type at least 32 bits wide.
Chris@16:      */
Chris@16:     template<class Iter>
Chris@16:     void generate(Iter first, Iter last) const
Chris@16:     {
Chris@16:         typedef typename std::iterator_traits<Iter>::value_type value_type;
Chris@16:         std::fill(first, last, static_cast<value_type>(0x8b8b8b8bu));
Chris@16:         std::size_t s = v.size();
Chris@16:         std::size_t n = last - first;
Chris@16:         std::size_t t =
Chris@16:             (n >= 623) ? 11 :
Chris@16:             (n >=  68) ?  7 :
Chris@16:             (n >=  39) ?  5 :
Chris@16:             (n >=   7) ?  3 :
Chris@16:             (n - 1)/2;
Chris@16:         std::size_t p = (n - t) / 2;
Chris@16:         std::size_t q = p + t;
Chris@16:         std::size_t m = (std::max)(s+1, n);
Chris@16:         value_type mask = 0xffffffffu;
Chris@16:         for(std::size_t k = 0; k < m; ++k) {
Chris@16:             value_type r1 =
Chris@16:                 *(first + k%n) ^ *(first + (k+p)%n) ^ *(first + (k+n-1)%n);
Chris@16:             r1 = r1 ^ (r1 >> 27);
Chris@16:             r1 = (r1 * 1664525u) & mask;
Chris@16:             value_type r2 = r1 +
Chris@16:                 ((k == 0) ? s :
Chris@16:                  (k <= s) ? k % n + v[k - 1] :
Chris@16:                  (k % n));
Chris@16:             *(first + (k+p)%n) = (*(first + (k+p)%n) + r1) & mask;
Chris@16:             *(first + (k+q)%n) = (*(first + (k+q)%n) + r2) & mask;
Chris@16:             *(first + k%n) = r2;
Chris@16:         }
Chris@16:         for(std::size_t k = m; k < m + n; ++k) {
Chris@16:             value_type r3 =
Chris@16:                 (*(first + k%n) + *(first + (k+p)%n) + *(first + (k+n-1)%n))
Chris@16:                 & mask;
Chris@16:             r3 = r3 ^ (r3 >> 27);
Chris@16:             r3 = (r3 * 1566083941u) & mask;
Chris@16:             value_type r4 = r3 - k%m;
Chris@16:             *(first + (k+p)%n) ^= r3;
Chris@16:             *(first + (k+q)%n) ^= r4;
Chris@16:             *(first + k%n) = r4;
Chris@16:         }
Chris@16:     }
Chris@16:     /** Returns the size of the sequence. */
Chris@16:     std::size_t size() const { return v.size(); }
Chris@16:     /** Writes the stored sequence to iter. */
Chris@16:     template<class Iter>
Chris@16:     void param(Iter out) { std::copy(v.begin(), v.end(), out); }
Chris@16: private:
Chris@16:     std::vector<result_type> v;
Chris@16: };
Chris@16: 
Chris@16: }
Chris@16: }
Chris@16: 
Chris@16: #endif