williamr@2: /* boost random/detail/signed_unsigned_compare.hpp header file
williamr@2:  *
williamr@2:  * Copyright Jens Maurer 2000-2001
williamr@2:  * Distributed under the Boost Software License, Version 1.0. (See
williamr@2:  * accompanying file LICENSE_1_0.txt or copy at
williamr@2:  * http://www.boost.org/LICENSE_1_0.txt)
williamr@2:  *
williamr@2:  * See http://www.boost.org for most recent version including documentation.
williamr@2:  *
williamr@2:  * Revision history
williamr@2:  */
williamr@2: 
williamr@2: 
williamr@2: #ifndef BOOST_RANDOM_DETAIL_SIGNED_UNSIGNED_COMPARE
williamr@2: #define BOOST_RANDOM_DETAIL_SIGNED_UNSIGNED_COMPARE
williamr@2: 
williamr@2: #include <boost/limits.hpp>
williamr@2: 
williamr@2: namespace boost {
williamr@2: namespace random {
williamr@2: 
williamr@2: /*
williamr@2:  * Correctly compare two numbers whose types possibly differ in signedness.
williamr@2:  * See boost::numeric_cast<> for the general idea.
williamr@2:  * Most "if" statements involve only compile-time constants, so the
williamr@2:  * optimizing compiler can do its job easily.
williamr@2:  *
williamr@2:  * With most compilers, the straightforward implementation produces a
williamr@2:  * bunch of (legitimate) warnings.  Some template magic helps, though.
williamr@2:  */
williamr@2: 
williamr@2: namespace detail {
williamr@2: template<bool signed1, bool signed2>
williamr@2: struct do_compare
williamr@2: { };
williamr@2: 
williamr@2: template<>
williamr@2: struct do_compare<false, false>
williamr@2: {
williamr@2:   // cast to the larger type is automatic with built-in types
williamr@2:   template<class T1, class T2>
williamr@2:   static bool equal(T1 x, T2 y) { return x == y; }
williamr@2:   template<class T1, class T2>
williamr@2:   static bool lessthan(T1 x, T2 y) { return x < y; }
williamr@2: };
williamr@2: 
williamr@2: template<>
williamr@2: struct do_compare<true, true> : do_compare<false, false>
williamr@2: { };
williamr@2: 
williamr@2: template<>
williamr@2: struct do_compare<true, false>
williamr@2: {
williamr@2:   template<class T1, class T2>
williamr@2:   static bool equal(T1 x, T2 y) { return x >= 0 && static_cast<T2>(x) == y; }
williamr@2:   template<class T1, class T2>
williamr@2:   static bool lessthan(T1 x, T2 y) { return x < 0 || static_cast<T2>(x) < y; }
williamr@2: };
williamr@2: 
williamr@2: template<>
williamr@2: struct do_compare<false, true>
williamr@2: {
williamr@2:   template<class T1, class T2>
williamr@2:   static bool equal(T1 x, T2 y) { return y >= 0 && x == static_cast<T1>(y); }
williamr@2:   template<class T1, class T2>
williamr@2:   static bool lessthan(T1 x, T2 y) { return y >= 0 && x < static_cast<T1>(y); }
williamr@2: };
williamr@2: 
williamr@2: } // namespace detail
williamr@2: 
williamr@2: 
williamr@2: template<class T1, class T2>
williamr@2: int equal_signed_unsigned(T1 x, T2 y)
williamr@2: {
williamr@2:   typedef std::numeric_limits<T1> x_traits;
williamr@2:   typedef std::numeric_limits<T2> y_traits;
williamr@2:   return detail::do_compare<x_traits::is_signed, y_traits::is_signed>::equal(x, y);
williamr@2: }
williamr@2: 
williamr@2: template<class T1, class T2>
williamr@2: int lessthan_signed_unsigned(T1 x, T2 y)
williamr@2: {
williamr@2:   typedef std::numeric_limits<T1> x_traits;
williamr@2:   typedef std::numeric_limits<T2> y_traits;
williamr@2:   return detail::do_compare<x_traits::is_signed, y_traits::is_signed>::lessthan(x, y);
williamr@2: }
williamr@2: 
williamr@2: } // namespace random
williamr@2: } // namespace boost
williamr@2: 
williamr@2: #endif // BOOST_RANDOM_DETAIL_SIGNED_UNSIGNED_COMPARE