num_cast.h

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/** @file
 *  @author Bram de Greve (bram@cocamware.com)
 *  @author Tom De Muer (tom@cocamware.com)
 *
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 *  The contents of this file are subject to the Common Public Attribution License 
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 *  the License. You may obtain a copy of the License at 
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 *  Mozilla Public License Version 1.1 but Sections 14 and 15 have been added to cover 
 *  use of software over a computer network and provide for limited attribution for 
 *  the Original Developer. In addition, Exhibit A has been modified to be consistent 
 *  with Exhibit B.
 *  
 *  Software distributed under the License is distributed on an "AS IS" basis, WITHOUT 
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 *  
 *  The Original Code is LASS - Library of Assembled Shared Sources.
 *  
 *  The Initial Developer of the Original Code is Bram de Greve and Tom De Muer.
 *  The Original Developer is the Initial Developer.
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 */
 
#ifndef LASS_GUARDIAN_OF_INCLUSION_NUM_NUM_CAST_H
#define LASS_GUARDIAN_OF_INCLUSION_NUM_NUM_CAST_H
 
#include "num_common.h"
 
namespace lass
{
namespace num
{
 
class BadNumCast: public util::ExceptionMixin<BadNumCast>
{
public:
    BadNumCast(std::string msg, std::string loc): util::ExceptionMixin<BadNumCast>(std::move(msg), std::move(loc)) {}
    ~BadNumCast() noexcept {}
};
 
namespace impl
{
 
template <typename Out, typename In, bool signedOut, bool signedIn> struct NumCaster;
 
template <typename Out, typename In>
struct NumCaster<Out, In, true, true>
{
    // Out is signed, In is signed
 
    static Out cast(In in)
    {
        static_assert(num::NumTraits<In>::isSigned == true);
        static_assert(num::NumTraits<Out>::isSigned == true);
 
        using TCommon = std::common_type_t<In, Out, int>;
        static_assert(num::NumTraits<TCommon>::isSigned == true);
 
        constexpr TCommon min = num::NumTraits<Out>::min;
        constexpr TCommon max = num::NumTraits<Out>::max;
        if (static_cast<TCommon>(in) < min)
        {
            LASS_THROW_EX(BadNumCast, "not a " << num::NumTraits<Out>::name() 
                << ": underflow: " << static_cast<TCommon>(in) << " < " << min);
        }
        if (static_cast<TCommon>(in) > max)
        {
            LASS_THROW_EX(BadNumCast, "not a " << num::NumTraits<Out>::name() 
                << ": overflow: " << static_cast<TCommon>(in) << " > " << max);
        }
        return static_cast<Out>(in);
    }
};
 
template <typename Out, typename In>
struct NumCaster<Out, In, false, true>
{
    // Out is unsigned, In is signed
 
    static Out cast(In in)
    {
        static_assert(num::NumTraits<In>::isSigned == true);
        static_assert(num::NumTraits<Out>::isSigned == false);
        using TUnsignedIn = typename num::NumTraits<In>::unsignedType;
 
        using TCommon = std::common_type_t<TUnsignedIn, Out, unsigned>;
        static_assert(num::NumTraits<TCommon>::isSigned == false);
 
        constexpr TCommon max = num::NumTraits<Out>::max;
        if (in < 0)
        {
            using TSigned = std::common_type_t<In, int>;
            LASS_THROW_EX(BadNumCast, "not a " << num::NumTraits<Out>::name() 
                << ": negative: " << static_cast<TSigned>(in));
        }
        if (static_cast<TCommon>(in) > max)
        {
            LASS_THROW_EX(BadNumCast, "not a " << num::NumTraits<Out>::name() 
                << ": overflow: " << static_cast<TCommon>(in) << " > " << max);
        }
        return static_cast<Out>(in);
    }
};
 
template <typename Out, typename In, bool signedOut>
struct NumCaster<Out, In, signedOut, false>
{
    // In is unsigned, Out is signed or unsigned
 
    static Out cast(In in)
    {
        static_assert(num::NumTraits<In>::isSigned == false);
        using TUnsignedOut = typename num::NumTraits<Out>::unsignedType;
 
        using TCommon = std::common_type_t<In, TUnsignedOut, unsigned>;
        static_assert(num::NumTraits<TCommon>::isSigned == false);
 
        constexpr TCommon max = num::NumTraits<Out>::max;
        if (static_cast<TCommon>(in) > max)
        {
            LASS_THROW_EX(BadNumCast, "not a " << num::NumTraits<Out>::name() 
                << ": overflow: " << static_cast<TCommon>(in) << " > " << max);
        }
        return static_cast<Out>(in);
    }
};
 
template <typename Out>
struct NumCaster<Out, Out, true, true>
{
    static Out cast(Out in) { return in; }
};
 
template <typename Out>
struct NumCaster<Out, Out, false, false>
{
    static Out cast(Out in) { return in; }
};
 
}
 
template <typename Out, typename In>
Out numCast(In in)
{
    return impl::NumCaster<Out, In, NumTraits<Out>::isSigned, NumTraits<In>::isSigned>::cast(in);
}
 
}
}
 
#endif
 
// EOF