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/* 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
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