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 //
 // buffers_iterator.hpp
 // ~~~~~~~~~~~~~~~~~~~~
 //
 // Copyright (c) 2003-2025 Christopher M. Kohlhoff (chris at kohlhoff dot com)
 //
 // Distributed under the Boost Software License, Version 1.0. (See accompanying
 // file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
 //
 
 #ifndef BOOST_ASIO_BUFFERS_ITERATOR_HPP
 #define BOOST_ASIO_BUFFERS_ITERATOR_HPP
 
 #if defined(_MSC_VER) && (_MSC_VER >= 1200)
 # pragma once
 #endif // defined(_MSC_VER) && (_MSC_VER >= 1200)
 
 #include <boost/asio/detail/config.hpp>
 #include <cstddef>
 #include <iterator>
 #include <boost/asio/buffer.hpp>
 #include <boost/asio/detail/assert.hpp>
 #include <boost/asio/detail/type_traits.hpp>
 
 #include <boost/asio/detail/push_options.hpp>
 
 namespace boost {
 namespace asio {
 
 namespace detail
 {
   template <bool IsMutable>
   struct buffers_iterator_types_helper;
 
   template <>
   struct buffers_iterator_types_helper<false>
   {
     typedef const_buffer buffer_type;
     template <typename ByteType>
     struct byte_type
     {
       typedef add_const_t<ByteType> type;
     };
   };
 
   template <>
   struct buffers_iterator_types_helper<true>
   {
     typedef mutable_buffer buffer_type;
     template <typename ByteType>
     struct byte_type
     {
       typedef ByteType type;
     };
   };
 
   template <typename BufferSequence, typename ByteType>
   struct buffers_iterator_types
   {
     enum
     {
       is_mutable = is_convertible<
           typename BufferSequence::value_type,
           mutable_buffer>::value
     };
     typedef buffers_iterator_types_helper<is_mutable> helper;
     typedef typename helper::buffer_type buffer_type;
     typedef typename helper::template byte_type<ByteType>::type byte_type;
     typedef typename BufferSequence::const_iterator const_iterator;
   };
 
   template <typename ByteType>
   struct buffers_iterator_types<mutable_buffer, ByteType>
   {
     typedef mutable_buffer buffer_type;
     typedef ByteType byte_type;
     typedef const mutable_buffer* const_iterator;
   };
 
   template <typename ByteType>
   struct buffers_iterator_types<const_buffer, ByteType>
   {
     typedef const_buffer buffer_type;
     typedef add_const_t<ByteType> byte_type;
     typedef const const_buffer* const_iterator;
   };
 } // namespace detail
 
 /// A random access iterator over the bytes in a buffer sequence.
 template <typename BufferSequence, typename ByteType = char>
 class buffers_iterator
 {
 private:
   typedef typename detail::buffers_iterator_types<
       BufferSequence, ByteType>::buffer_type buffer_type;
 
   typedef typename detail::buffers_iterator_types<BufferSequence,
           ByteType>::const_iterator buffer_sequence_iterator_type;
 
 public:
   /// The type used for the distance between two iterators.
   typedef std::ptrdiff_t difference_type;
 
   /// The type of the value pointed to by the iterator.
   typedef ByteType value_type;
 
 #if defined(GENERATING_DOCUMENTATION)
   /// The type of the result of applying operator->() to the iterator.
   /**
    * If the buffer sequence stores buffer objects that are convertible to
    * mutable_buffer, this is a pointer to a non-const ByteType. Otherwise, a
    * pointer to a const ByteType.
    */
   typedef const_or_non_const_ByteType* pointer;
 #else // defined(GENERATING_DOCUMENTATION)
   typedef typename detail::buffers_iterator_types<
       BufferSequence, ByteType>::byte_type* pointer;
 #endif // defined(GENERATING_DOCUMENTATION)
 
 #if defined(GENERATING_DOCUMENTATION)
   /// The type of the result of applying operator*() to the iterator.
   /**
    * If the buffer sequence stores buffer objects that are convertible to
    * mutable_buffer, this is a reference to a non-const ByteType. Otherwise, a
    * reference to a const ByteType.
    */
   typedef const_or_non_const_ByteType& reference;
 #else // defined(GENERATING_DOCUMENTATION)
   typedef typename detail::buffers_iterator_types<
       BufferSequence, ByteType>::byte_type& reference;
 #endif // defined(GENERATING_DOCUMENTATION)
 
   /// The iterator category.
   typedef std::random_access_iterator_tag iterator_category;
 
   /// Default constructor. Creates an iterator in an undefined state.
   buffers_iterator()
     : current_buffer_(),
       current_buffer_position_(0),
       begin_(),
       current_(),
       end_(),
       position_(0)
   {
   }
 
   /// Construct an iterator representing the beginning of the buffers' data.
   static buffers_iterator begin(const BufferSequence& buffers)
 #if defined(__GNUC__) && (__GNUC__ == 4) && (__GNUC_MINOR__ == 3)
     __attribute__ ((__noinline__))
 #endif // defined(__GNUC__) && (__GNUC__ == 4) && (__GNUC_MINOR__ == 3)
   {
     buffers_iterator new_iter;
     new_iter.begin_ = boost::asio::buffer_sequence_begin(buffers);
     new_iter.current_ = boost::asio::buffer_sequence_begin(buffers);
     new_iter.end_ = boost::asio::buffer_sequence_end(buffers);
     while (new_iter.current_ != new_iter.end_)
     {
       new_iter.current_buffer_ = *new_iter.current_;
       if (new_iter.current_buffer_.size() > 0)
         break;
       ++new_iter.current_;
     }
     return new_iter;
   }
 
   /// Construct an iterator representing the end of the buffers' data.
   static buffers_iterator end(const BufferSequence& buffers)
 #if defined(__GNUC__) && (__GNUC__ == 4) && (__GNUC_MINOR__ == 3)
     __attribute__ ((__noinline__))
 #endif // defined(__GNUC__) && (__GNUC__ == 4) && (__GNUC_MINOR__ == 3)
   {
     buffers_iterator new_iter;
     new_iter.begin_ = boost::asio::buffer_sequence_begin(buffers);
     new_iter.current_ = boost::asio::buffer_sequence_begin(buffers);
     new_iter.end_ = boost::asio::buffer_sequence_end(buffers);
     while (new_iter.current_ != new_iter.end_)
     {
       buffer_type buffer = *new_iter.current_;
       new_iter.position_ += buffer.size();
       ++new_iter.current_;
     }
     return new_iter;
   }
 
   /// Dereference an iterator.
   reference operator*() const
   {
     return dereference();
   }
 
   /// Dereference an iterator.
   pointer operator->() const
   {
     return &dereference();
   }
 
   /// Access an individual element.
   reference operator[](std::ptrdiff_t difference) const
   {
     buffers_iterator tmp(*this);
     tmp.advance(difference);
     return *tmp;
   }
 
   /// Increment operator (prefix).
   buffers_iterator& operator++()
   {
     increment();
     return *this;
   }
 
   /// Increment operator (postfix).
   buffers_iterator operator++(int)
   {
     buffers_iterator tmp(*this);
     ++*this;
     return tmp;
   }
 
   /// Decrement operator (prefix).
   buffers_iterator& operator--()
   {
     decrement();
     return *this;
   }
 
   /// Decrement operator (postfix).
   buffers_iterator operator--(int)
   {
     buffers_iterator tmp(*this);
     --*this;
     return tmp;
   }
 
   /// Addition operator.
   buffers_iterator& operator+=(std::ptrdiff_t difference)
   {
     advance(difference);
     return *this;
   }
 
   /// Subtraction operator.
   buffers_iterator& operator-=(std::ptrdiff_t difference)
   {
     advance(-difference);
     return *this;
   }
 
   /// Addition operator.
   friend buffers_iterator operator+(const buffers_iterator& iter,
       std::ptrdiff_t difference)
   {
     buffers_iterator tmp(iter);
     tmp.advance(difference);
     return tmp;
   }
 
   /// Addition operator.
   friend buffers_iterator operator+(std::ptrdiff_t difference,
       const buffers_iterator& iter)
   {
     buffers_iterator tmp(iter);
     tmp.advance(difference);
     return tmp;
   }
 
   /// Subtraction operator.
   friend buffers_iterator operator-(const buffers_iterator& iter,
       std::ptrdiff_t difference)
   {
     buffers_iterator tmp(iter);
     tmp.advance(-difference);
     return tmp;
   }
 
   /// Subtraction operator.
   friend std::ptrdiff_t operator-(const buffers_iterator& a,
       const buffers_iterator& b)
   {
     return b.distance_to(a);
   }
 
   /// Test two iterators for equality.
   friend bool operator==(const buffers_iterator& a, const buffers_iterator& b)
   {
     return a.equal(b);
   }
 
   /// Test two iterators for inequality.
   friend bool operator!=(const buffers_iterator& a, const buffers_iterator& b)
   {
     return !a.equal(b);
   }
 
   /// Compare two iterators.
   friend bool operator<(const buffers_iterator& a, const buffers_iterator& b)
   {
     return a.distance_to(b) > 0;
   }
 
   /// Compare two iterators.
   friend bool operator<=(const buffers_iterator& a, const buffers_iterator& b)
   {
     return !(b < a);
   }
 
   /// Compare two iterators.
   friend bool operator>(const buffers_iterator& a, const buffers_iterator& b)
   {
     return b < a;
   }
 
   /// Compare two iterators.
   friend bool operator>=(const buffers_iterator& a, const buffers_iterator& b)
   {
     return !(a < b);
   }
 
 private:
   // Dereference the iterator.
   reference dereference() const
   {
     return static_cast<pointer>(
         current_buffer_.data())[current_buffer_position_];
   }
 
   // Compare two iterators for equality.
   bool equal(const buffers_iterator& other) const
   {
     return position_ == other.position_;
   }
 
   // Increment the iterator.
   void increment()
   {
     BOOST_ASIO_ASSERT(current_ != end_ && "iterator out of bounds");
     ++position_;
 
     // Check if the increment can be satisfied by the current buffer.
     ++current_buffer_position_;
     if (current_buffer_position_ != current_buffer_.size())
       return;
 
     // Find the next non-empty buffer.
     ++current_;
     current_buffer_position_ = 0;
     while (current_ != end_)
     {
       current_buffer_ = *current_;
       if (current_buffer_.size() > 0)
         return;
       ++current_;
     }
   }
 
   // Decrement the iterator.
   void decrement()
   {
     BOOST_ASIO_ASSERT(position_ > 0 && "iterator out of bounds");
     --position_;
 
     // Check if the decrement can be satisfied by the current buffer.
     if (current_buffer_position_ != 0)
     {
       --current_buffer_position_;
       return;
     }
 
     // Find the previous non-empty buffer.
     buffer_sequence_iterator_type iter = current_;
     while (iter != begin_)
     {
       --iter;
       buffer_type buffer = *iter;
       std::size_t buffer_size = buffer.size();
       if (buffer_size > 0)
       {
         current_ = iter;
         current_buffer_ = buffer;
         current_buffer_position_ = buffer_size - 1;
         return;
       }
     }
   }
 
   // Advance the iterator by the specified distance.
   void advance(std::ptrdiff_t n)
   {
     if (n > 0)
     {
       BOOST_ASIO_ASSERT(current_ != end_ && "iterator out of bounds");
       for (;;)
       {
         std::ptrdiff_t current_buffer_balance
           = current_buffer_.size() - current_buffer_position_;
 
         // Check if the advance can be satisfied by the current buffer.
         if (current_buffer_balance > n)
         {
           position_ += n;
           current_buffer_position_ += n;
           return;
         }
 
         // Update position.
         n -= current_buffer_balance;
         position_ += current_buffer_balance;
 
         // Move to next buffer. If it is empty then it will be skipped on the
         // next iteration of this loop.
         if (++current_ == end_)
         {
           BOOST_ASIO_ASSERT(n == 0 && "iterator out of bounds");
           current_buffer_ = buffer_type();
           current_buffer_position_ = 0;
           return;
         }
         current_buffer_ = *current_;
         current_buffer_position_ = 0;
       }
     }
     else if (n < 0)
     {
       std::size_t abs_n = -n;
       BOOST_ASIO_ASSERT(position_ >= abs_n && "iterator out of bounds");
       for (;;)
       {
         // Check if the advance can be satisfied by the current buffer.
         if (current_buffer_position_ >= abs_n)
         {
           position_ -= abs_n;
           current_buffer_position_ -= abs_n;
           return;
         }
 
         // Update position.
         abs_n -= current_buffer_position_;
         position_ -= current_buffer_position_;
 
         // Check if we've reached the beginning of the buffers.
         if (current_ == begin_)
         {
           BOOST_ASIO_ASSERT(abs_n == 0 && "iterator out of bounds");
           current_buffer_position_ = 0;
           return;
         }
 
         // Find the previous non-empty buffer.
         buffer_sequence_iterator_type iter = current_;
         while (iter != begin_)
         {
           --iter;
           buffer_type buffer = *iter;
           std::size_t buffer_size = buffer.size();
           if (buffer_size > 0)
           {
             current_ = iter;
             current_buffer_ = buffer;
             current_buffer_position_ = buffer_size;
             break;
           }
         }
       }
     }
   }
 
   // Determine the distance between two iterators.
   std::ptrdiff_t distance_to(const buffers_iterator& other) const
   {
     return other.position_ - position_;
   }
 
   buffer_type current_buffer_;
   std::size_t current_buffer_position_;
   buffer_sequence_iterator_type begin_;
   buffer_sequence_iterator_type current_;
   buffer_sequence_iterator_type end_;
   std::size_t position_;
 };
 
 /// Construct an iterator representing the beginning of the buffers' data.
 template <typename BufferSequence>
 inline buffers_iterator<BufferSequence> buffers_begin(
     const BufferSequence& buffers)
 {
   return buffers_iterator<BufferSequence>::begin(buffers);
 }
 
 /// Construct an iterator representing the end of the buffers' data.
 template <typename BufferSequence>
 inline buffers_iterator<BufferSequence> buffers_end(
     const BufferSequence& buffers)
 {
   return buffers_iterator<BufferSequence>::end(buffers);
 }
 
 } // namespace asio
 } // namespace boost
 
 #include <boost/asio/detail/pop_options.hpp>
 
 #endif // BOOST_ASIO_BUFFERS_ITERATOR_HPP

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