Chris@16: /* boost random/generate_canonical.hpp header file
Chris@16:  *
Chris@16:  * Copyright Steven Watanabe 2011
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_GENERATE_CANONICAL_HPP
Chris@16: #define BOOST_RANDOM_GENERATE_CANONICAL_HPP
Chris@16: 
Chris@16: #include <algorithm>
Chris@16: #include <boost/assert.hpp>
Chris@16: #include <boost/config/no_tr1/cmath.hpp>
Chris@16: #include <boost/limits.hpp>
Chris@16: #include <boost/type_traits/is_integral.hpp>
Chris@101: #include <boost/mpl/bool.hpp>
Chris@16: #include <boost/random/detail/signed_unsigned_tools.hpp>
Chris@16: #include <boost/random/detail/generator_bits.hpp>
Chris@16: 
Chris@16: namespace boost {
Chris@16: namespace random {
Chris@16: 
Chris@16: namespace detail {
Chris@16: 
Chris@16: template<class RealType, std::size_t bits, class URNG>
Chris@16: RealType generate_canonical_impl(URNG& g, boost::mpl::true_ /*is_integral*/)
Chris@16: {
Chris@16:     using std::pow;
Chris@16:     typedef typename URNG::result_type base_result;
Chris@16:     std::size_t digits = std::numeric_limits<RealType>::digits;
Chris@16:     RealType R = RealType((g.max)()) - RealType((g.min)()) + 1;
Chris@16:     RealType mult = R;
Chris@16:     RealType limit =
Chris@16:         pow(RealType(2),
Chris@16:             RealType((std::min)(static_cast<std::size_t>(bits), digits)));
Chris@16:     RealType S = RealType(detail::subtract<base_result>()(g(), (g.min)()));
Chris@16:     while(mult < limit) {
Chris@16:         RealType inc = RealType(detail::subtract<base_result>()(g(), (g.min)()));
Chris@16:         S += inc * mult;
Chris@16:         mult *= R;
Chris@16:     }
Chris@16:     return S / mult;
Chris@16: }
Chris@16: 
Chris@16: template<class RealType, std::size_t bits, class URNG>
Chris@16: RealType generate_canonical_impl(URNG& g, boost::mpl::false_ /*is_integral*/)
Chris@16: {
Chris@16:     using std::pow;
Chris@16:     using std::floor;
Chris@16:     BOOST_ASSERT((g.min)() == 0);
Chris@16:     BOOST_ASSERT((g.max)() == 1);
Chris@16:     std::size_t digits = std::numeric_limits<RealType>::digits;
Chris@16:     std::size_t engine_bits = detail::generator_bits<URNG>::value();
Chris@16:     std::size_t b = (std::min)(bits, digits);
Chris@16:     RealType R = pow(RealType(2), RealType(engine_bits));
Chris@16:     RealType mult = R;
Chris@16:     RealType limit = pow(RealType(2), RealType(b));
Chris@16:     RealType S = RealType(g() - (g.min)());
Chris@16:     while(mult < limit) {
Chris@16:         RealType inc(floor((RealType(g()) - RealType((g.min)())) * R));
Chris@16:         S += inc * mult;
Chris@16:         mult *= R;
Chris@16:     }
Chris@16:     return S / mult;
Chris@16: }
Chris@16: 
Chris@16: }
Chris@16: 
Chris@16: /**
Chris@16:  * Returns a value uniformly distributed in the range [0, 1)
Chris@16:  * with at least @c bits random bits.
Chris@16:  */
Chris@16: template<class RealType, std::size_t bits, class URNG>
Chris@16: RealType generate_canonical(URNG& g)
Chris@16: {
Chris@16:     RealType result = detail::generate_canonical_impl<RealType, bits>(
Chris@16:         g, boost::is_integral<typename URNG::result_type>());
Chris@16:     BOOST_ASSERT(result >= 0);
Chris@16:     BOOST_ASSERT(result <= 1);
Chris@16:     if(result == 1) {
Chris@16:         result -= std::numeric_limits<RealType>::epsilon() / 2;
Chris@16:         BOOST_ASSERT(result != 1);
Chris@16:     }
Chris@16:     return result;
Chris@16: }
Chris@16: 
Chris@16: } // namespace random
Chris@16: } // namespace boost
Chris@16: 
Chris@16: #endif // BOOST_RANDOM_GENERATE_CANONICAL_HPP