97 lines
3.0 KiB
C++
97 lines
3.0 KiB
C++
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/* boost random/generate_canonical.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_GENERATE_CANONICAL_HPP
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#define BOOST_RANDOM_GENERATE_CANONICAL_HPP
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#include <algorithm>
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#include <boost/assert.hpp>
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#include <boost/config/no_tr1/cmath.hpp>
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#include <boost/limits.hpp>
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#include <boost/type_traits/is_integral.hpp>
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#include <boost/mpl/bool.hpp>
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#include <boost/random/detail/signed_unsigned_tools.hpp>
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#include <boost/random/detail/generator_bits.hpp>
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namespace boost {
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namespace random {
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namespace detail {
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template<class RealType, std::size_t bits, class URNG>
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RealType generate_canonical_impl(URNG& g, boost::mpl::true_ /*is_integral*/)
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{
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using std::pow;
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typedef typename URNG::result_type base_result;
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std::size_t digits = std::numeric_limits<RealType>::digits;
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RealType R = RealType((g.max)()) - RealType((g.min)()) + 1;
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RealType mult = R;
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RealType limit =
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pow(RealType(2),
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RealType((std::min)(static_cast<std::size_t>(bits), digits)));
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RealType S = RealType(detail::subtract<base_result>()(g(), (g.min)()));
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while(mult < limit) {
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RealType inc = RealType(detail::subtract<base_result>()(g(), (g.min)()));
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S += inc * mult;
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mult *= R;
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}
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return S / mult;
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}
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template<class RealType, std::size_t bits, class URNG>
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RealType generate_canonical_impl(URNG& g, boost::mpl::false_ /*is_integral*/)
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{
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using std::pow;
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using std::floor;
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BOOST_ASSERT((g.min)() == 0);
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BOOST_ASSERT((g.max)() == 1);
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std::size_t digits = std::numeric_limits<RealType>::digits;
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std::size_t engine_bits = detail::generator_bits<URNG>::value();
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std::size_t b = (std::min)(bits, digits);
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RealType R = pow(RealType(2), RealType(engine_bits));
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RealType mult = R;
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RealType limit = pow(RealType(2), RealType(b));
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RealType S = RealType(g() - (g.min)());
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while(mult < limit) {
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RealType inc(floor((RealType(g()) - RealType((g.min)())) * R));
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S += inc * mult;
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mult *= R;
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}
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return S / mult;
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}
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}
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/**
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* Returns a value uniformly distributed in the range [0, 1)
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* with at least @c bits random bits.
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*/
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template<class RealType, std::size_t bits, class URNG>
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RealType generate_canonical(URNG& g)
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{
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RealType result = detail::generate_canonical_impl<RealType, bits>(
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g, boost::random::traits::is_integral<typename URNG::result_type>());
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BOOST_ASSERT(result >= 0);
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BOOST_ASSERT(result <= 1);
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if(result == 1) {
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result -= std::numeric_limits<RealType>::epsilon() / 2;
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BOOST_ASSERT(result != 1);
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}
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return result;
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}
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} // namespace random
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} // namespace boost
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#endif // BOOST_RANDOM_GENERATE_CANONICAL_HPP
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