// 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, InputIt, T>(std::move(first), std::move(last), i);
}
}
