text: // Copyright (c) 2014-2018, The Monero Project
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  // Parts of this file are originally copyright (c) 2012-2013 The Cryptonote developers
  
  #pragma once
  
  #include <limits>
  #include <type_traits>
  #include <utility>
  #include <sstream>
  #include <string>
  /*! \file varint.h
   * \brief provides the implementation of varint's
   * 
   * The representation of varints is rather odd. The first bit of each
   * octet is significant, it represents wheter there is another part
   * waiting to be read. For example 0x8002 would return 0x200, even
   * though 0x02 does not have its msb set. The actual way they are read
   * is as follows: Strip the msb of each byte, then from left to right,
   * read in what remains, placing it in reverse, into the buffer. Thus,
   * the following bit stream: 0xff02 would return 0x027f. 0xff turns
   * into 0x7f, is placed on the beginning of the buffer, then 0x02 is
   * unchanged, since its msb is not set, and placed at the end of the
   * buffer.
   */
  
  namespace tools {
  
    /*! \brief Error codes for varint
     */
    enum {
      /* \brief Represents the overflow error */
      EVARINT_OVERFLOW = -1,
      /* \brief Represents a non conical represnetation */
      EVARINT_REPRESENT = -2,
    };
  
    /*! \brief writes a varint to a stream.
     */
    template<typename OutputIt, typename T>
    /* Requires T to be both an integral type and unsigned, should be a compile error if it is not */
    typename std::enable_if<std::is_integral<T>::value && std::is_unsigned<T>::value, void>::type 
    write_varint(OutputIt &&dest, T i) {
      /* Make sure that there is one after this */
      while (i >= 0x80) {
        *dest = (static_cast<char>(i) & 0x7f) | 0x80; 
        ++dest;
        i >>= 7;			/* I should be in multiples of 7, this should just get the next part */
      }
      /* writes the last one to dest */
      *dest = static_cast<char>(i);
      dest++;			/* Seems kinda pointless... */
    }
  
    /*! \brief Returns the string that represents the varint
     */
    template<typename T>
      std::string get_varint_data(const T& v)
      {
        std::stringstream ss;
        write_varint(std::ostreambuf_iterator<char>(ss), v);
        return ss.str();
      }
    /*! \brief reads in the varint that is pointed to by InputIt into write
     */ 
    template<int bits, typename InputIt, typename T>
      typename std::enable_if<std::is_integral<T>::value && std::is_unsigned<T>::value && 0 <= bits && bits <= std::numeric_limits<T>::digits, int>::type
      read_varint(InputIt &&first, InputIt &&last, T &write) {
      int read = 0;
      write = 0;
      for (int shift = 0;; shift += 7) {
        if (first == last) {
  	return read; 
        }
        unsigned char byte = *first;
        ++first;
        ++read;
        if (shift + 7 >= bits && byte >= 1 << (bits - shift)) {
  	return EVARINT_OVERFLOW;
        }
        if (byte == 0 && shift != 0) {
  	return EVARINT_REPRESENT;
        }
  
        write |= static_cast<T>(byte & 0x7f) << shift; /* Does the actually placing into write, stripping the first bit */
  
        /* If there is no next */
        if ((byte & 0x80) == 0) {
  	break;
        }
      }
      return read;
    }
  
    /*! \brief Wrapper around the other read_varint,
     *  Sets template parameters for you.
     */
    template<typename InputIt, typename T>
      int read_varint(InputIt &&first, InputIt &&last, T &i) {
      return read_varint<std::numeric_limits<T>::digits>(std::forward<InputIt>(first), std::forward<InputIt>(last), i);
    }
  }
  