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