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/*
Copyright (c) 2003 - 2005, Arvid Norberg, Daniel Wallin
All rights reserved.

Redistribution and use in source and binary forms, with or without
modification, are permitted provided that the following conditions
are met:

    * Redistributions of source code must retain the above copyright
      notice, this list of conditions and the following disclaimer.
    * Redistributions in binary form must reproduce the above copyright
      notice, this list of conditions and the following disclaimer in
      the documentation and/or other materials provided with the distribution.
    * Neither the name of Rasterbar Software nor the names of its
      contributors may be used to endorse or promote products derived
      from this software without specific prior written permission.

THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE
LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
POSSIBILITY OF SUCH DAMAGE.

*/

#ifndef LIBTORRENT_BUFFER_HPP
#define LIBTORRENT_BUFFER_HPP

//#define TORRENT_BUFFER_DEBUG

#include "libtorrent/invariant_check.hpp"
#include <memory>

namespace libtorrent {

class buffer
{
public:
    struct interval
    {
       interval(char* begin, char* end)
          : begin(begin)
          , end(end)
        {}

        char operator[](int index) const
        {
            assert(begin + index < end);
            return begin[index];
        }
                  
        int left() const { assert(end >= begin); return end - begin; }

        char* begin;
        char* end;
    };

    struct const_interval
    {
       const_interval(char const* begin, char const* end)
          : begin(begin)
          , end(end)
        {}

        char operator[](int index) const
        {
            assert(begin + index < end);
            return begin[index];
        }

        int left() const { assert(end >= begin); return end - begin; }

        char const* begin;
        char const* end;
    };

    typedef std::pair<const_interval, const_interval> interval_type;

    buffer(std::size_t n = 0);
    ~buffer();

    interval allocate(std::size_t n);
    void insert(char const* first, char const* last);
    void erase(std::size_t n);
    std::size_t size() const;
    std::size_t capacity() const;
    void reserve(std::size_t n);
    interval_type data() const;
    bool empty() const;

    std::size_t space_left() const;

    char const* raw_data() const
    {
        return m_first;
    }

#ifndef NDEBUG
    void check_invariant() const;
#endif
         
private:
    char* m_first;
    char* m_last;
    char* m_write_cursor;
    char* m_read_cursor;
    char* m_read_end;
    bool m_empty;
#ifdef TORRENT_BUFFER_DEBUG
    mutable std::vector<char> m_debug;
    mutable int m_pending_copy;
#endif
};

inline buffer::buffer(std::size_t n)
        : m_first((char*)::operator new(n))
        , m_last(m_first + n)
        , m_write_cursor(m_first)
        , m_read_cursor(m_first)
        , m_read_end(m_last)
        , m_empty(true)
{
#ifdef TORRENT_BUFFER_DEBUG
        m_pending_copy = 0;
#endif
}

inline buffer::~buffer()
{
    ::operator delete (m_first);
}

inline buffer::interval buffer::allocate(std::size_t n)
{
        assert(m_read_cursor <= m_read_end || m_empty);

        INVARIANT_CHECK;
        
#ifdef TORRENT_BUFFER_DEBUG
        if (m_pending_copy)
        {
                std::copy(m_write_cursor - m_pending_copy, m_write_cursor
                        , m_debug.end() - m_pending_copy);
                m_pending_copy = 0;
        }
        m_debug.resize(m_debug.size() + n);
        m_pending_copy = n;
#endif
        if (m_read_cursor < m_write_cursor || m_empty)
        {
        // ..R***W..
                if (m_last - m_write_cursor >= (std::ptrdiff_t)n)
                {
                        interval ret(m_write_cursor, m_write_cursor + n);
                        m_write_cursor += n;
                        m_read_end = m_write_cursor;
                        assert(m_read_cursor <= m_read_end);
                        if (n) m_empty = false;
                        return ret;
                }

                if (m_read_cursor - m_first >= (std::ptrdiff_t)n)
                {
                        m_read_end = m_write_cursor;
                        interval ret(m_first, m_first + n);
                        m_write_cursor = m_first + n;
                        assert(m_read_cursor <= m_read_end);
                        if (n) m_empty = false;
                        return ret;
                }

                reserve(capacity() + n - (m_last - m_write_cursor));
                assert(m_last - m_write_cursor >= (std::ptrdiff_t)n);
                interval ret(m_write_cursor, m_write_cursor + n);
                m_write_cursor += n;
                m_read_end = m_write_cursor;
                if (n) m_empty = false;
                assert(m_read_cursor <= m_read_end);
                return ret;

        }
        //**W...R**
        if (m_read_cursor - m_write_cursor >= (std::ptrdiff_t)n)
        {
                interval ret(m_write_cursor, m_write_cursor + n);
                m_write_cursor += n;
                if (n) m_empty = false;
                return ret;
        }
        reserve(capacity() + n - (m_read_cursor - m_write_cursor));
        assert(m_read_cursor - m_write_cursor >= (std::ptrdiff_t)n);
        interval ret(m_write_cursor, m_write_cursor + n);
        m_write_cursor += n;
        if (n) m_empty = false;
        return ret;
}

inline void buffer::insert(char const* first, char const* last)
{
    INVARIANT_CHECK;

    std::size_t n = last - first;

#ifdef TORRENT_BUFFER_DEBUG
        if (m_pending_copy)
        {
                std::copy(m_write_cursor - m_pending_copy, m_write_cursor
                        , m_debug.end() - m_pending_copy);
                m_pending_copy = 0;
        }
        m_debug.insert(m_debug.end(), first, last);
#endif

    if (space_left() < n)
    {
        reserve(capacity() + n);
    }

    m_empty = false;

    char const* end = (m_last - m_write_cursor) < (std::ptrdiff_t)n ? 
        m_last : m_write_cursor + n;

    std::size_t copied = end - m_write_cursor;
    std::memcpy(m_write_cursor, first, copied);

    m_write_cursor += copied;
         if (m_write_cursor > m_read_end) m_read_end = m_write_cursor;
    first += copied;
    n -= copied;

    if (n == 0) return;

         assert(m_write_cursor == m_last);
    m_write_cursor = m_first;

    memcpy(m_write_cursor, first, n);
    m_write_cursor += n;
}

inline void buffer::erase(std::size_t n)
{
        INVARIANT_CHECK;

        if (n == 0) return;
        assert(!m_empty);
         
#ifndef NDEBUG
        int prev_size = size();
#endif
        assert(m_read_cursor <= m_read_end);
        m_read_cursor += n;
        if (m_read_cursor > m_read_end)
        {
                m_read_cursor = m_first + (m_read_cursor - m_read_end);
                assert(m_read_cursor <= m_write_cursor);
        }

        m_empty = m_read_cursor == m_write_cursor;

        assert(prev_size - n == size());

#ifdef TORRENT_BUFFER_DEBUG
        m_debug.erase(m_debug.begin(), m_debug.begin() + n);
#endif
}

inline std::size_t buffer::size() const
{
    // ...R***W.
    if (m_read_cursor < m_write_cursor)
    {
        return m_write_cursor - m_read_cursor;
    }
    // ***W..R*
    else
    {
        if (m_empty) return 0;
        return (m_write_cursor - m_first) + (m_read_end - m_read_cursor);
    }
}

inline std::size_t buffer::capacity() const
{
    return m_last - m_first;
}

inline void buffer::reserve(std::size_t size)
{
    std::size_t n = (std::size_t)(capacity() * 1.f);
    if (n < size) n = size;

    char* buf = (char*)::operator new(n);
    char* old = m_first;

    if (m_read_cursor < m_write_cursor)
    {
    // ...R***W.<>.
        std::memcpy(
            buf + (m_read_cursor - m_first)
          , m_read_cursor
          , m_write_cursor - m_read_cursor
        );

        m_write_cursor = buf + (m_write_cursor - m_first);
        m_read_cursor = buf + (m_read_cursor - m_first);
                  m_read_end = m_write_cursor;
        m_first = buf;
        m_last = buf + n;
    }
    else
    {
    // **W..<>.R**
        std::size_t skip = n - (m_last - m_first);

        std::memcpy(buf, m_first, m_write_cursor - m_first);
        std::memcpy(
            buf + (m_read_cursor - m_first) + skip
          , m_read_cursor
          , m_last - m_read_cursor
        );

        m_write_cursor = buf + (m_write_cursor - m_first);

        if (!m_empty)
                  {
            m_read_cursor = buf + (m_read_cursor - m_first) + skip;
            m_read_end = buf + (m_read_end - m_first) + skip;
                  }
        else
                  {
            m_read_cursor = m_write_cursor;
                                m_read_end = m_write_cursor;
                  }

        m_first = buf;
        m_last = buf + n;
    }

    ::operator delete (old);
}

#ifndef NDEBUG
inline void buffer::check_invariant() const
{
        assert(m_read_end >= m_read_cursor);
        assert(m_last >= m_read_cursor);
        assert(m_last >= m_write_cursor);
        assert(m_last >= m_first);
        assert(m_first <= m_read_cursor);
        assert(m_first <= m_write_cursor);
#ifdef TORRENT_BUFFER_DEBUG
        int a = m_debug.size();
        int b = size();
        (void)a;
        (void)b;
        assert(m_debug.size() == size());
#endif
}
#endif

inline buffer::interval_type buffer::data() const
{
        INVARIANT_CHECK;

#ifdef TORRENT_BUFFER_DEBUG
        if (m_pending_copy)
        {
                std::copy(m_write_cursor - m_pending_copy, m_write_cursor
                        , m_debug.end() - m_pending_copy);
                m_pending_copy = 0;
        }
#endif

    // ...R***W.
    if (m_read_cursor < m_write_cursor)
    {
#ifdef TORRENT_BUFFER_DEBUG
        assert(m_debug.size() == size());
        assert(std::equal(m_debug.begin(), m_debug.end(), m_read_cursor));
#endif
        return interval_type(
            const_interval(m_read_cursor, m_write_cursor)
          , const_interval(m_last, m_last)
        );
    }
    // **W...R**
    else
    {
        if (m_read_cursor == m_read_end)
                  {
#ifdef TORRENT_BUFFER_DEBUG
                assert(m_debug.size() == size());
                assert(std::equal(m_debug.begin(), m_debug.end(), m_first));
#endif

            return interval_type(
                const_interval(m_first, m_write_cursor)
                , const_interval(m_last, m_last));
                  }
#ifdef TORRENT_BUFFER_DEBUG
        assert(m_debug.size() == size());
        assert(std::equal(m_debug.begin(), m_debug.begin() + (m_read_end
            - m_read_cursor), m_read_cursor));
        assert(std::equal(m_debug.begin() + (m_read_end - m_read_cursor), m_debug.end()
            , m_first));
#endif

        assert(m_read_cursor <= m_read_end || m_empty);
        return interval_type(
            const_interval(m_read_cursor, m_read_end)
          , const_interval(m_first, m_write_cursor)
        );
    }
}

inline bool buffer::empty() const
{
    return m_empty;
}

inline std::size_t buffer::space_left() const
{
    if (m_empty) return m_last - m_first;

    // ...R***W.
    if (m_read_cursor < m_write_cursor)
    {
        return (m_last - m_write_cursor) + (m_read_cursor - m_first);
    }
    // ***W..R*
    else
    {
        return m_read_cursor - m_write_cursor;
    }
}

}

#endif // LIBTORRENT_BUFFER_HPP

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