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