Boost C++ Libraries

boost/dll/detail/aggressive_ptr_cast.hpp

// Copyright 2014 Renato Tegon Forti, Antony Polukhin.
// Copyright 2015-2016 Antony Polukhin.
//
// 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)

#ifndef BOOST_DLL_DETAIL_AGGRESSIVE_PTR_CAST_HPP
#define BOOST_DLL_DETAIL_AGGRESSIVE_PTR_CAST_HPP

#include <boost/config.hpp>
#ifdef BOOST_HAS_PRAGMA_ONCE
#   pragma once
#endif

#include <boost/static_assert.hpp>
#include <boost/type_traits/is_pointer.hpp>
#include <boost/type_traits/is_member_pointer.hpp>
#include <boost/type_traits/is_void.hpp>
#include <boost/type_traits/is_reference.hpp>
#include <boost/type_traits/remove_pointer.hpp>
#include <boost/type_traits/remove_reference.hpp>
#include <boost/utility/enable_if.hpp>
#include <boost/cstdint.hpp>    // boost::uintptr_t
#include <cstring>              // std::memcpy

namespace boost { namespace dll { namespace detail {

// GCC warns when reinterpret_cast between function pointer and object pointer occur.
// This method suppress the warnings and ensures that such casts are safe.
template <class To, class From>
BOOST_FORCEINLINE typename boost::disable_if_c<boost::is_member_pointer<To>::value || boost::is_reference<To>::value || boost::is_member_pointer<From>::value, To>::type
    aggressive_ptr_cast(From v) BOOST_NOEXCEPT
{
    BOOST_STATIC_ASSERT_MSG(
        boost::is_pointer<To>::value && boost::is_pointer<From>::value,
        "`agressive_ptr_cast` function must be used only for pointer casting."
    );

    BOOST_STATIC_ASSERT_MSG(
        boost::is_void< typename boost::remove_pointer<To>::type >::value
        || boost::is_void< typename boost::remove_pointer<From>::type >::value,
        "`agressive_ptr_cast` function must be used only for casting to or from void pointers."
    );

    BOOST_STATIC_ASSERT_MSG(
        sizeof(v) == sizeof(To),
        "Pointer to function and pointer to object differ in size on your platform."
    );

    return reinterpret_cast<To>(
        reinterpret_cast<boost::uintptr_t>(v)
    );
}

template <class To, class From>
BOOST_FORCEINLINE typename boost::disable_if_c<!boost::is_reference<To>::value || boost::is_member_pointer<From>::value, To>::type
    aggressive_ptr_cast(From v) BOOST_NOEXCEPT
{
    BOOST_STATIC_ASSERT_MSG(
        boost::is_pointer<From>::value,
        "`agressive_ptr_cast` function must be used only for pointer casting."
    );

    BOOST_STATIC_ASSERT_MSG(
        boost::is_void< typename boost::remove_pointer<From>::type >::value,
        "`agressive_ptr_cast` function must be used only for casting to or from void pointers."
    );

    BOOST_STATIC_ASSERT_MSG(
        sizeof(v) == sizeof(typename boost::remove_reference<To>::type*),
        "Pointer to function and pointer to object differ in size on your platform."
    );

    return static_cast<To>(
        *reinterpret_cast<typename boost::remove_reference<To>::type*>(
            *reinterpret_cast<boost::uintptr_t*>(
                reinterpret_cast<unsigned char*>(
                    v
                )
            )
        )
    );
}

template <class To, class From>
BOOST_FORCEINLINE typename boost::disable_if_c<!boost::is_member_pointer<To>::value || boost::is_member_pointer<From>::value, To>::type
    aggressive_ptr_cast(From v) BOOST_NOEXCEPT
{
    BOOST_STATIC_ASSERT_MSG(
        boost::is_pointer<From>::value,
        "`agressive_ptr_cast` function must be used only for pointer casting."
    );

    BOOST_STATIC_ASSERT_MSG(
        boost::is_void< typename boost::remove_pointer<From>::type >::value,
        "`agressive_ptr_cast` function must be used only for casting to or from void pointers."
    );

    To res = 0;
    std::memcpy(&res, &v, sizeof(To));
    return res;
}

template <class To, class From>
BOOST_FORCEINLINE typename boost::disable_if_c<boost::is_member_pointer<To>::value || !boost::is_member_pointer<From>::value, To>::type
    aggressive_ptr_cast(From /* v */) BOOST_NOEXCEPT
{
    BOOST_STATIC_ASSERT_MSG(
        boost::is_pointer<To>::value,
        "`agressive_ptr_cast` function must be used only for pointer casting."
    );

    BOOST_STATIC_ASSERT_MSG(
        boost::is_void< typename boost::remove_pointer<To>::type >::value,
        "`agressive_ptr_cast` function must be used only for casting to or from void pointers."
    );

    BOOST_STATIC_ASSERT_MSG(
        !sizeof(From),
        "Casting from member pointers to void pointer is not implemnted in `agressive_ptr_cast`."
    );

    return 0;
}

}}} // boost::dll::detail

#endif // BOOST_DLL_DETAIL_AGGRESSIVE_PTR_CAST_HPP