bitsery/include/BufferReader.h

//MIT License
//
//Copyright (c) 2017 Mindaugas Vinkelis
//
//Permission is hereby granted, free of charge, to any person obtaining a copy
//of this software and associated documentation files (the "Software"), to deal
//in the Software without restriction, including without limitation the rights
//to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
//copies of the Software, and to permit persons to whom the Software is
//furnished to do so, subject to the following conditions:
//
//The above copyright notice and this permission notice shall be included in all
//copies or substantial portions of the Software.
//
//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.



#ifndef BITSERY_BUFFER_READER_H
#define BITSERY_BUFFER_READER_H

#include "Common.h"

#include <cassert>
#include <algorithm>

namespace bitsery {

    struct BufferReader {

        using value_type = uint8_t;

        BufferReader(const std::vector<uint8_t> &buf)
                : _pos{buf.data()},
                  _end{buf.data() + buf.size()} {

        }

        BufferReader(const uint8_t* data, size_t size)
                : _pos{data},
                  _end{data + size}
        {
        }
        template <size_t N>
        BufferReader(const uint8_t (&data)[N])
                : _pos{data},
                  _end{data + N}
        {
        }


        template<size_t SIZE, typename T>
        bool readBytes(T &v) {
            static_assert(std::is_integral<T>(), "");
            static_assert(sizeof(T) == SIZE, "");
            using UT = typename std::make_unsigned<T>::type;
            return !m_scratch
                   ? directRead(&v, 1)
                   : readBits(reinterpret_cast<UT &>(v), BITS_SIZE<T>);
        }

        template<size_t SIZE, typename T>
        bool readBuffer(T *buf, size_t count) {
            static_assert(std::is_integral<T>(), "");
            static_assert(sizeof(T) == SIZE, "");

            if (!m_scratchBits) {
                return directRead(buf, count);
            } else {
                using UT = typename std::make_unsigned<T>::type;
                //todo improve implementation
                const auto end = buf + count;
                for (auto it = buf; it != end; ++it) {
                    if (!readBits(reinterpret_cast<UT &>(*it), BITS_SIZE<T>))
                        return false;
                }
            }
            return true;
        }


        template<typename T>
        bool readBits(T &v, size_t bitsCount) {
            static_assert(std::is_integral<T>() && std::is_unsigned<T>(), "");
            assert(bitsCount <= BITS_SIZE<T>);

            const auto bytesRequired = bitsCount > m_scratchBits
                                       ? ((bitsCount - 1 - m_scratchBits) >> 3) + 1u
                                       : 0u;
            if (static_cast<size_t>(std::distance(_pos, _end)) < bytesRequired)
                return false;
            readBitsInternal(v, bitsCount);
            return true;
        }

        bool align() {
            if (m_scratchBits) {
                SCRATCH_TYPE tmp{};
                readBitsInternal(tmp, BITS_SIZE<value_type> - m_scratchBits);
                return tmp == 0;
            }
            return true;
        }

        bool isCompleted() const {
            return _pos == _end;
        }

    private:
        const value_type* _pos;
        const value_type* _end;

        template<typename T>
        bool directRead(T *v, size_t count) {
            static_assert(!std::is_const<T>::value, "");
            const auto bytesCount = sizeof(T) * count;
            if (static_cast<size_t>(std::distance(_pos, _end)) < bytesCount)
                return false;
            std::copy_n(_pos, bytesCount, reinterpret_cast<value_type *>(v));
            std::advance(_pos, bytesCount);
            return true;
        }

        template<typename T>
        void readBitsInternal(T &v, size_t size) {
            auto bitsLeft = size;
            T res{};
            while (bitsLeft > 0) {
                auto bits = std::min(bitsLeft, BITS_SIZE<value_type>);
                if (m_scratchBits < bits) {
                    value_type tmp;

                    std::copy_n(_pos, 1, reinterpret_cast<value_type *>(&tmp));
                    std::advance(_pos, 1);

                    m_scratch |= static_cast<SCRATCH_TYPE>(tmp) << m_scratchBits;
                    m_scratchBits += BITS_SIZE<value_type>;
                }
                auto shiftedRes =
                        static_cast<T>(m_scratch & ((static_cast<SCRATCH_TYPE>(1) << bits) - 1)) << (size - bitsLeft);
                res |= shiftedRes;
                m_scratch >>= bits;
                m_scratchBits -= bits;
                bitsLeft -= bits;
            }
            v = res;
        }

        using SCRATCH_TYPE = typename BIGGER_TYPE<value_type>::type;

        SCRATCH_TYPE m_scratch{};
        size_t m_scratchBits{};                                    ///< Number of bits currently in the scratch buffer. If the user wants to read more bits than this, we have to go fetch another dword from memory.

    };

}

#endif //BITSERY_BUFFER_READER_H