/* boost random/detail/signed_unsigned_compare.hpp header file

 *

 * Copyright Jens Maurer 2000-2001

 * 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.

 *

 * Revision history

 */

#ifndef BOOST_RANDOM_DETAIL_SIGNED_UNSIGNED_COMPARE

#define BOOST_RANDOM_DETAIL_SIGNED_UNSIGNED_COMPARE

#include <boost/limits.hpp>

namespace boost {

namespace random {

/*

 * Correctly compare two numbers whose types possibly differ in signedness.

 * See boost::numeric_cast<> for the general idea.

 * Most "if" statements involve only compile-time constants, so the

 * optimizing compiler can do its job easily.

 *

 * With most compilers, the straightforward implementation produces a

 * bunch of (legitimate) warnings.  Some template magic helps, though.

 */

namespace detail {

template<bool signed1, bool signed2>

struct do_compare

{ };

template<>

struct do_compare<false, false>

{

  // cast to the larger type is automatic with built-in types

  template<class T1, class T2>

  static bool equal(T1 x, T2 y) { return x == y; }

  template<class T1, class T2>

  static bool lessthan(T1 x, T2 y) { return x < y; }

};

template<>

struct do_compare<true, true> : do_compare<false, false>

{ };

template<>

struct do_compare<true, false>

{

  template<class T1, class T2>

  static bool equal(T1 x, T2 y) { return x >= 0 && static_cast<T2>(x) == y; }

  template<class T1, class T2>

  static bool lessthan(T1 x, T2 y) { return x < 0 || static_cast<T2>(x) < y; }

};

template<>

struct do_compare<false, true>

{

  template<class T1, class T2>

  static bool equal(T1 x, T2 y) { return y >= 0 && x == static_cast<T1>(y); }

  template<class T1, class T2>

  static bool lessthan(T1 x, T2 y) { return y >= 0 && x < static_cast<T1>(y); }

};

} // namespace detail

template<class T1, class T2>

int equal_signed_unsigned(T1 x, T2 y)

{

  typedef std::numeric_limits<T1> x_traits;

  typedef std::numeric_limits<T2> y_traits;

  return detail::do_compare<x_traits::is_signed, y_traits::is_signed>::equal(x, y);

}

template<class T1, class T2>

int lessthan_signed_unsigned(T1 x, T2 y)

{

  typedef std::numeric_limits<T1> x_traits;

  typedef std::numeric_limits<T2> y_traits;

  return detail::do_compare<x_traits::is_signed, y_traits::is_signed>::lessthan(x, y);

}

} // namespace random

} // namespace boost

#endif // BOOST_RANDOM_DETAIL_SIGNED_UNSIGNED_COMPARE