GSL/gsl/gsl_byte

///////////////////////////////////////////////////////////////////////////////
//
// Copyright (c) 2015 Microsoft Corporation. All rights reserved.
//
// This code is licensed under the MIT License (MIT).
//
// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
// THE SOFTWARE.
//
///////////////////////////////////////////////////////////////////////////////

#pragma once

#ifndef GSL_BYTE_H
#define GSL_BYTE_H

#ifdef _MSC_VER

// MSVC 2013 workarounds
#if _MSC_VER <= 1800

// constexpr is not understood
#pragma push_macro("constexpr")
#define constexpr /*constexpr*/

// noexcept is not understood
#pragma push_macro("noexcept")
#define noexcept /*noexcept*/

#endif // _MSC_VER <= 1800

#endif // _MSC_VER

namespace gsl
{
// This is a simple definition for now that allows
// use of byte within span<> to be standards-compliant
enum class byte : unsigned char
{
};

template <class IntegerType, class = std::enable_if_t<std::is_integral<IntegerType>::value>>
constexpr byte& operator<<=(byte& b, IntegerType shift) noexcept
{
    return b = byte(static_cast<unsigned char>(b) << shift);
}

template <class IntegerType, class = std::enable_if_t<std::is_integral<IntegerType>::value>>
constexpr byte operator<<(byte b, IntegerType shift) noexcept
{
    return byte(static_cast<unsigned char>(b) << shift);
}

template <class IntegerType, class = std::enable_if_t<std::is_integral<IntegerType>::value>>
constexpr byte& operator>>=(byte& b, IntegerType shift) noexcept
{
    return b = byte(static_cast<unsigned char>(b) >> shift);
}

template <class IntegerType, class = std::enable_if_t<std::is_integral<IntegerType>::value>>
constexpr byte operator>>(byte b, IntegerType shift) noexcept
{
    return byte(static_cast<unsigned char>(b) >> shift);
}

constexpr byte& operator|=(byte& l, byte r) noexcept
{
    return l = byte(static_cast<unsigned char>(l) | static_cast<unsigned char>(r));
}

constexpr byte operator|(byte l, byte r) noexcept
{
    return byte(static_cast<unsigned char>(l) + static_cast<unsigned char>(r));
}

constexpr byte& operator&=(byte& l, byte r) noexcept
{
    return l = byte(static_cast<unsigned char>(l) & static_cast<unsigned char>(r));
}

constexpr byte operator&(byte l, byte r) noexcept
{
    return byte(static_cast<unsigned char>(l) & static_cast<unsigned char>(r));
}

constexpr byte& operator^=(byte& l, byte r) noexcept
{
    return l = byte(static_cast<unsigned char>(l) ^ static_cast<unsigned char>(r));
}

constexpr byte operator^(byte l, byte r) noexcept
{
    return byte(static_cast<unsigned char>(l) ^ static_cast<unsigned char>(r));
}

constexpr byte operator~(byte b) noexcept { return byte(~static_cast<unsigned char>(b)); }

template <class IntegerType, class = std::enable_if_t<std::is_integral<IntegerType>::value>>
constexpr IntegerType to_integer(byte b) noexcept
{
    return {b};
}

template<bool, typename T>
constexpr byte to_byte_impl(T t) noexcept
{
    static_assert(
        false, 
        "gsl::to_byte(t) must be provided an unsigned char, otherwise data loss may occur. "
        "If you are calling to_byte with an integer contant use: gsl::to_byte<t>() version."
    )
}
template<>
constexpr byte to_byte_impl<true, unsigned char>(unsigned char t) noexcept
{
     return byte(t);
}

template<typename T>
constexpr byte to_byte(T t) noexcept
{
     return to_byte_impl<std::is_same<T, unsigned char>::value, T>(t);
}

template <int I>
constexpr byte to_byte() noexcept
{
    static_assert(I >= 0 && I <= 255, "gsl::byte only has 8 bits of storage, values must be in range 0-255");
    return static_cast<byte>(I);
}

} // namespace gsl

#ifdef _MSC_VER

#if _MSC_VER <= 1800

#undef constexpr
#pragma pop_macro("constexpr")

#undef noexcept
#pragma pop_macro("noexcept")

#endif // _MSC_VER <= 1800

#endif // _MSC_VER

#endif // GSL_BYTE_H