text: //  Copyright (c) 2007 John Maddock
  //  Use, modification and distribution are subject to 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)
  
  #ifndef BOOST_MATH_COS_PI_HPP
  #define BOOST_MATH_COS_PI_HPP
  
  #ifdef _MSC_VER
  #pragma once
  #endif
  
  #include <boost/config/no_tr1/cmath.hpp>
  #include <boost/math/tools/config.hpp>
  #include <boost/math/special_functions/trunc.hpp>
  #include <boost/math/tools/promotion.hpp>
  #include <boost/math/constants/constants.hpp>
  
  namespace boost{ namespace math{ namespace detail{
  
  template <class T, class Policy>
  T cos_pi_imp(T x, const Policy& pol)
  {
     BOOST_MATH_STD_USING // ADL of std names
     // cos of pi*x:
     bool invert = false;
     if(x < 0.5)
        return cos(constants::pi<T>() * x);
     if(x < 1)
     {
        x = -x;
     }
  
     T rem = floor(x);
     if(itrunc(rem, pol) & 1)
        invert = !invert;
     rem = x - rem;
     if(rem > 0.5f)
     {
        rem = 1 - rem;
        invert = !invert;
     }
     if(rem == 0.5f)
        return 0;
     
     rem = cos(constants::pi<T>() * rem);
     return invert ? T(-rem) : rem;
  }
  
  } // namespace detail
  
  template <class T, class Policy>
  inline typename tools::promote_args<T>::type cos_pi(T x, const Policy& pol)
  {
     typedef typename tools::promote_args<T>::type result_type;
     return boost::math::detail::cos_pi_imp<result_type>(x, pol);
  }
  
  template <class T>
  inline typename tools::promote_args<T>::type cos_pi(T x)
  {
     return boost::math::cos_pi(x, policies::policy<>());
  }
  
  } // namespace math
  } // namespace boost
  #endif
  
  