90 lines
2.6 KiB
Plaintext
90 lines
2.6 KiB
Plaintext
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/* boost random/detail/signed_unsigned_tools.hpp header file
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*
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* Copyright Jens Maurer 2006
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* Distributed under the Boost Software License, Version 1.0. (See
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* accompanying file LICENSE_1_0.txt or copy at
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* http://www.boost.org/LICENSE_1_0.txt)
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*
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* See http://www.boost.org for most recent version including documentation.
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*/
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#ifndef BOOST_RANDOM_DETAIL_SIGNED_UNSIGNED_TOOLS
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#define BOOST_RANDOM_DETAIL_SIGNED_UNSIGNED_TOOLS
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#include <boost/limits.hpp>
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#include <boost/config.hpp>
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#include <boost/random/traits.hpp>
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namespace boost {
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namespace random {
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namespace detail {
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/*
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* Compute x - y, we know that x >= y, return an unsigned value.
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*/
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template<class T, bool sgn = std::numeric_limits<T>::is_signed && std::numeric_limits<T>::is_bounded>
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struct subtract { };
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template<class T>
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struct subtract<T, /* signed */ false>
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{
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typedef T result_type;
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result_type operator()(T x, T y) { return x - y; }
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};
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template<class T>
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struct subtract<T, /* signed */ true>
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{
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typedef typename boost::random::traits::make_unsigned_or_unbounded<T>::type result_type;
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result_type operator()(T x, T y)
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{
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if (y >= 0) // because x >= y, it follows that x >= 0, too
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return result_type(x) - result_type(y);
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if (x >= 0) // y < 0
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// avoid the nasty two's complement case for y == min()
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return result_type(x) + result_type(-(y+1)) + 1;
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// both x and y are negative: no signed overflow
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return result_type(x - y);
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}
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};
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/*
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* Compute x + y, x is unsigned, result fits in type of "y".
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*/
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template<class T1, class T2, bool sgn = (std::numeric_limits<T2>::is_signed && (std::numeric_limits<T1>::digits >= std::numeric_limits<T2>::digits))>
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struct add { };
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template<class T1, class T2>
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struct add<T1, T2, /* signed or else T2 has more digits than T1 so the cast always works - needed when T2 is a multiprecision type and T1 is a native integer */ false>
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{
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typedef T2 result_type;
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result_type operator()(T1 x, T2 y) { return T2(x) + y; }
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};
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template<class T1, class T2>
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struct add<T1, T2, /* signed */ true>
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{
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typedef T2 result_type;
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result_type operator()(T1 x, T2 y)
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{
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if (y >= 0)
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return T2(x) + y;
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// y < 0
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if (x > T1(-(y+1))) // result >= 0 after subtraction
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// avoid the nasty two's complement edge case for y == min()
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return T2(x - T1(-(y+1)) - 1);
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// abs(x) < abs(y), thus T2 able to represent x
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return T2(x) + y;
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}
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};
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} // namespace detail
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} // namespace random
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} // namespace boost
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#endif // BOOST_RANDOM_DETAIL_SIGNED_UNSIGNED_TOOLS
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