FixedBitLength.h

//
// Copyright 2015 - 2026 (C). Alex Robenko. All rights reserved.
//
// SPDX-License-Identifier: MPL-2.0
//
// This Source Code Form is subject to the terms of the Mozilla Public
// License, v. 2.0. If a copy of the MPL was not distributed with this
// file, You can obtain one at http://mozilla.org/MPL/2.0/.
 
#pragma once
 
#include "comms/Assert.h"
#include "comms/details/tag.h"
#include "comms/ErrorStatus.h"
#include "comms/util/SizeToType.h"
#include "comms/util/BitSizeToByteSize.h"
#include "comms/util/type_traits.h"
 
#include <cstddef>
#include <limits>
 
namespace comms
{
 
namespace field
{
 
namespace adapter
{
 
template <std::size_t TLen, bool TSignExtend, typename TBase>
class FixedBitLength : public TBase
{
    using BaseImpl = TBase;
    using BaseSerialisedType = typename BaseImpl::SerialisedType;
    using BaseUnsignedSerialisedType = typename std::make_unsigned<BaseSerialisedType>::type;
 
    static const std::size_t BitLength = TLen;
    static const std::size_t Length =
        comms::util::BitSizeToByteSize<BitLength>::Value;
 
    static_assert(0 < BitLength, "Bit length is expected to be greater than 0");
    static_assert(Length <= sizeof(BaseSerialisedType),
        "The provided length limit is too big");
 
public:
 
    using ValueType = typename BaseImpl::ValueType;
 
    using SerialisedType =
        typename comms::util::Conditional<
            (Length < sizeof(BaseSerialisedType))
        >::template Type<
            typename comms::util::SizeToType<Length, std::is_signed<BaseSerialisedType>::value>::Type,
            BaseSerialisedType
        >;
 
    using Endian = typename BaseImpl::Endian;
 
    FixedBitLength() = default;
 
    explicit FixedBitLength(const ValueType& val)
      : BaseImpl(val)
    {
    }
 
    FixedBitLength(const FixedBitLength&) = default;
    FixedBitLength(FixedBitLength&&) = default;
    FixedBitLength& operator=(const FixedBitLength&) = default;
    FixedBitLength& operator=(FixedBitLength&&) = default;
 
    static constexpr std::size_t length()
    {
        return Length;
    }
 
    static constexpr std::size_t minLength()
    {
        return length();
    }
 
    static constexpr std::size_t maxLength()
    {
        return length();
    }
 
    static constexpr SerialisedType toSerialised(ValueType val)
    {
        return adjustToSerialised(BaseImpl::toSerialised(val), HasSignTag<>());
    }
 
    static constexpr ValueType fromSerialised(SerialisedType val)
    {
        return BaseImpl::fromSerialised(adjustFromSerialised(val, HasSignTag<>()));
    }
 
    template <typename TIter>
    comms::ErrorStatus read(TIter& iter, std::size_t size)
    {
        if (size < length()) {
            return comms::ErrorStatus::NotEnoughData;
        }
 
        readNoStatus(iter);
        return comms::ErrorStatus::Success;
    }
 
    template <typename TIter>
    void readNoStatus(TIter& iter)
    {
        auto serialisedValue =
            comms::util::readData<SerialisedType, Length>(iter, Endian());
        BaseImpl::setValue(fromSerialised(serialisedValue));
    }
 
    template <typename TIter>
    comms::ErrorStatus write(TIter& iter, std::size_t size) const
    {
        if (size < length()) {
            return comms::ErrorStatus::BufferOverflow;
        }
 
        writeNoStatus(iter);
        return comms::ErrorStatus::Success;
    }
 
    template <typename TIter>
    void writeNoStatus(TIter& iter) const
    {
        BaseImpl::template writeData<Length>(toSerialised(BaseImpl::getValue()), iter);
    }
 
private:
    template <typename... TParams>
    using UnsignedTag = comms::details::tag::Tag1<>;
 
    template <typename... TParams>
    using SignedTag = comms::details::tag::Tag2<>;
 
    template <typename... TParams>
    using NoSignExtTag = comms::details::tag::Tag3<>;
 
    template <typename... TParams>
    using MustSignExtTag = comms::details::tag::Tag4<>;
 
    template <typename...>
    using HasSignTag =
        typename comms::util::LazyShallowConditional<
            TSignExtend && std::is_signed<SerialisedType>::value
        >::template Type<
            SignedTag,
            UnsignedTag
        >;
 
    using UnsignedSerialisedType = typename std::make_unsigned<SerialisedType>::type;
 
    template <typename... TParams>
    static SerialisedType adjustToSerialised(BaseSerialisedType val, UnsignedTag<TParams...>)
    {
        return static_cast<SerialisedType>(static_cast<BaseUnsignedSerialisedType>(val) & UnsignedValueMask);
    }
 
    template <typename... TParams>
    static SerialisedType adjustToSerialised(BaseSerialisedType val, SignedTag<TParams...>)
    {
        auto valueTmp =
            static_cast<UnsignedSerialisedType>(
                static_cast<BaseUnsignedSerialisedType>(val) & UnsignedValueMask);
 
        return signExtUnsignedSerialised(valueTmp);
    }
 
    template <typename... TParams>
    static BaseSerialisedType adjustFromSerialised(SerialisedType val, UnsignedTag<TParams...>)
    {
        return static_cast<BaseSerialisedType>(static_cast<UnsignedSerialisedType>(val) & UnsignedValueMask);
    }
 
    template <typename... TParams>
    static BaseSerialisedType adjustFromSerialised(SerialisedType val, SignedTag<TParams...>)
    {
        auto valueTmp =
            static_cast<UnsignedSerialisedType>(
                static_cast<UnsignedSerialisedType>(val) & UnsignedValueMask);
        return
            static_cast<BaseSerialisedType>(
                signExtUnsignedSerialised(valueTmp));
    }
 
    static SerialisedType signExtUnsignedSerialised(UnsignedSerialisedType val)
    {
        using SignExtTag =
            typename comms::util::LazyShallowConditional<
                BitLength < static_cast<std::size_t>(std::numeric_limits<UnsignedSerialisedType>::digits)
            >::template Type<
                MustSignExtTag,
                NoSignExtTag
            >;
        return signExtUnsignedSerialisedInternal(val, SignExtTag());
    }
 
    template <typename... TParams>
    static SerialisedType signExtUnsignedSerialisedInternal(UnsignedSerialisedType val, MustSignExtTag<TParams...>)
    {
        static_assert(
            BitLength < std::numeric_limits<UnsignedSerialisedType>::digits,
            "BitLength is expected to be less than number of bits in the value type");
 
        static const auto SignExtMask =
            static_cast<UnsignedSerialisedType>(
                ~((static_cast<UnsignedSerialisedType>(1U) << BitLength) - 1));
 
        static const auto SignMask =
            static_cast<UnsignedSerialisedType>(
                static_cast<UnsignedSerialisedType>(1U) << (BitLength - 1));
 
        if ((val & SignMask) != 0) {
            val |= SignExtMask;
        }
        return static_cast<SerialisedType>(val);
    }
 
    template <typename... TParams>
    static SerialisedType signExtUnsignedSerialisedInternal(UnsignedSerialisedType val, NoSignExtTag<TParams...>)
    {
        return static_cast<SerialisedType>(val);
    }
 
private:
    static const UnsignedSerialisedType UnsignedValueMask =
        (static_cast<UnsignedSerialisedType>(1U) << BitLength) - 1;
};
 
}  // namespace adapter
 
}  // namespace field
 
}  // namespace comms