Chris@16: /* boost random/detail/signed_unsigned_tools.hpp header file
Chris@16:  *
Chris@16:  * Copyright Jens Maurer 2006
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@16: 
Chris@16: #ifndef BOOST_RANDOM_DETAIL_SIGNED_UNSIGNED_TOOLS
Chris@16: #define BOOST_RANDOM_DETAIL_SIGNED_UNSIGNED_TOOLS
Chris@16: 
Chris@16: #include <boost/limits.hpp>
Chris@16: #include <boost/config.hpp>
Chris@16: #include <boost/type_traits/make_unsigned.hpp>
Chris@16: 
Chris@16: namespace boost {
Chris@16: namespace random {
Chris@16: namespace detail {
Chris@16: 
Chris@16: 
Chris@16: /*
Chris@16:  * Compute x - y, we know that x >= y, return an unsigned value.
Chris@16:  */
Chris@16: 
Chris@16: template<class T, bool sgn = std::numeric_limits<T>::is_signed>
Chris@16: struct subtract { };
Chris@16: 
Chris@16: template<class T>
Chris@16: struct subtract<T, /* signed */ false>
Chris@16: {
Chris@16:   typedef T result_type;
Chris@16:   result_type operator()(T x, T y) { return x - y; }
Chris@16: };
Chris@16: 
Chris@16: template<class T>
Chris@16: struct subtract<T, /* signed */ true>
Chris@16: {
Chris@16:   typedef typename make_unsigned<T>::type result_type;
Chris@16:   result_type operator()(T x, T y)
Chris@16:   {
Chris@16:     if (y >= 0)   // because x >= y, it follows that x >= 0, too
Chris@16:       return result_type(x) - result_type(y);
Chris@16:     if (x >= 0)   // y < 0
Chris@16:       // avoid the nasty two's complement case for y == min()
Chris@16:       return result_type(x) + result_type(-(y+1)) + 1;
Chris@16:     // both x and y are negative: no signed overflow
Chris@16:     return result_type(x - y);
Chris@16:   }
Chris@16: };
Chris@16: 
Chris@16: /*
Chris@16:  * Compute x + y, x is unsigned, result fits in type of "y".
Chris@16:  */
Chris@16: 
Chris@16: template<class T1, class T2, bool sgn = std::numeric_limits<T2>::is_signed>
Chris@16: struct add { };
Chris@16: 
Chris@16: template<class T1, class T2>
Chris@16: struct add<T1, T2, /* signed */ false>
Chris@16: {
Chris@16:   typedef T2 result_type;
Chris@16:   result_type operator()(T1 x, T2 y) { return T2(x) + y; }
Chris@16: };
Chris@16: 
Chris@16: template<class T1, class T2>
Chris@16: struct add<T1, T2, /* signed */ true>
Chris@16: {
Chris@16:   typedef T2 result_type;
Chris@16:   result_type operator()(T1 x, T2 y)
Chris@16:   {
Chris@16:     if (y >= 0)
Chris@16:       return T2(x) + y;
Chris@16:     // y < 0
Chris@16:     if (x > T1(-(y+1)))  // result >= 0 after subtraction
Chris@16:       // avoid the nasty two's complement edge case for y == min()
Chris@16:       return T2(x - T1(-(y+1)) - 1);
Chris@16:     // abs(x) < abs(y), thus T2 able to represent x
Chris@16:     return T2(x) + y;
Chris@16:   }
Chris@16: };
Chris@16: 
Chris@16: } // namespace detail
Chris@16: } // namespace random
Chris@16: } // namespace boost
Chris@16: 
Chris@16: #endif // BOOST_RANDOM_DETAIL_SIGNED_UNSIGNED_TOOLS
Chris@16: