promote_integral.hpp

// Boost.GIL (Generic Image Library)
//
// Copyright (c) 2015, Oracle and/or its affiliates.
// Contributed and/or modified by Menelaos Karavelas, on behalf of Oracle
// 
// Copyright (c) 2020, Debabrata Mandal <mandaldebabrata123@gmail.com>
//
// Licensed under the Boost Software License version 1.0.
// http://www.boost.org/users/license.html
//
// Source: Boost.Geometry (aka GGL, Generic Geometry Library)
// Modifications: adapted for Boost.GIL
//  - Rename namespace boost::geometry to boost::gil
//  - Rename include guards
//  - Remove support for boost::multiprecision types
//  - Remove support for 128-bit integer types
//  - Replace mpl meta functions with mp11 equivalents
//
#ifndef BOOST_GIL_PROMOTE_INTEGRAL_HPP
#define BOOST_GIL_PROMOTE_INTEGRAL_HPP

#include <boost/mp11/list.hpp>

#include <climits>
#include <cstddef>
#include <type_traits>

namespace boost { namespace gil
{

namespace detail { namespace promote_integral
{

// meta-function that returns the bit size of a type
template
<
    typename T,
    bool IsFundamental = std::is_fundamental<T>::value
>
struct bit_size {};

// for fundamental types, just return CHAR_BIT * sizeof(T)
template <typename T>
struct bit_size<T, true> : std::integral_constant<std::size_t, (CHAR_BIT * sizeof(T))> {};

template
<
    typename T,
    typename IntegralTypes,
    std::size_t MinSize
>
struct promote_to_larger
{
    using current_type = boost::mp11::mp_first<IntegralTypes>;
    using list_after_front = boost::mp11::mp_rest<IntegralTypes>;

    using type = typename std::conditional
        <
            (bit_size<current_type>::value >= MinSize),
            current_type,
            typename promote_to_larger
                <
                    T,
                    list_after_front,
                    MinSize
                >::type
        >::type;
};

// The following specialization is required to finish the loop over
// all list elements
template <typename T, std::size_t MinSize>
struct promote_to_larger<T, boost::mp11::mp_list<>, MinSize>
{
    // if promotion fails, keep the number T
    // (and cross fingers that overflow will not occur)
    using type = T;
};

}} // namespace detail::promote_integral

template
<
    typename T,
    bool PromoteUnsignedToUnsigned = false,
    bool UseCheckedInteger = false,
    bool IsIntegral = std::is_integral<T>::value
>
class promote_integral
{
private:
    static bool const is_unsigned = std::is_unsigned<T>::value;

    using bit_size_type = detail::promote_integral::bit_size<T>;

    // Define the minimum size (in bits) needed for the promoted type
    // If T is the input type and P the promoted type, then the
    // minimum number of bits for P are (below b stands for the number
    // of bits of T):
    // * if T is unsigned and P is unsigned: 2 * b
    // * if T is signed and P is signed: 2 * b - 1
    // * if T is unsigned and P is signed: 2 * b + 1
    using min_bit_size_type = typename std::conditional
        <
            (PromoteUnsignedToUnsigned && is_unsigned),
            std::integral_constant<std::size_t, (2 * bit_size_type::value)>,
            typename std::conditional
                <
                    is_unsigned,
                    std::integral_constant<std::size_t, (2 * bit_size_type::value + 1)>,
                    std::integral_constant<std::size_t, (2 * bit_size_type::value - 1)>
                >::type
        >::type;

    // Define the list of signed integral types we are going to use
    // for promotion
    using signed_integral_types = boost::mp11::mp_list
        <
            short, int, long
#if defined(BOOST_HAS_LONG_LONG)
            , boost::long_long_type
#endif
        >;

    // Define the list of unsigned integral types we are going to use
    // for promotion
    using unsigned_integral_types = boost::mp11::mp_list
        <
            unsigned short, unsigned int, unsigned long, std::size_t
#if defined(BOOST_HAS_LONG_LONG)
            , boost::ulong_long_type
#endif
        >;

    // Define the list of integral types that will be used for
    // promotion (depending in whether we was to promote unsigned to
    // unsigned or not)
    using integral_types = typename std::conditional
        <
            (is_unsigned && PromoteUnsignedToUnsigned),
            unsigned_integral_types,
            signed_integral_types
        >::type;

public:
    using type = typename detail::promote_integral::promote_to_larger
        <
            T,
            integral_types,
            min_bit_size_type::value
        >::type;
};


template <typename T, bool PromoteUnsignedToUnsigned, bool UseCheckedInteger>
class promote_integral
    <
        T, PromoteUnsignedToUnsigned, UseCheckedInteger, false
    >
{
public:
    using type = T;
};

}} // namespace boost::gil

#endif // BOOST_GIL_PROMOTE_INTEGRAL_HPP