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129 lines
4.8 KiB
C++
129 lines
4.8 KiB
C++
// Copyright (c) 2014-2016, The Monero Project
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//
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// All rights reserved.
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//
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// Redistribution and use in source and binary forms, with or without modification, are
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// permitted provided that the following conditions are met:
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//
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// 1. Redistributions of source code must retain the above copyright notice, this list of
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// conditions and the following disclaimer.
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//
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// 2. Redistributions in binary form must reproduce the above copyright notice, this list
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// of conditions and the following disclaimer in the documentation and/or other
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// materials provided with the distribution.
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//
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// 3. Neither the name of the copyright holder nor the names of its contributors may be
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// used to endorse or promote products derived from this software without specific
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// prior written permission.
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//
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// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND ANY
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// EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF
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// MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL
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// THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
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// SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
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// PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
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// INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT,
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// STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF
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// THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
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//
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// Parts of this file are originally copyright (c) 2012-2013 The Cryptonote developers
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#pragma once
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#include <limits>
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#include <type_traits>
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#include <utility>
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#include <sstream>
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#include <string>
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/*! \file varint.h
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* \breif provides the implementation of varint's
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*
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* The representation of varints is rather odd. The first bit of each
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* octet is significant, it represents wheter there is another part
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* waiting to be read. For example 0x8002 would return 0x200, even
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* though 0x02 does not have its msb set. The actual way they are read
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* is as follows: Strip the msb of each byte, then from left to right,
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* read in what remains, placing it in reverse, into the buffer. Thus,
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* the following bit stream: 0xff02 would return 0x027f. 0xff turns
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* into 0x7f, is placed on the beggining of the buffer, then 0x02 is
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* unchanged, since its msb is not set, and placed at the end of the
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* buffer.
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*/
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namespace tools {
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/*! \brief Error codes for varint
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*/
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enum {
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/* \brief Represents the overflow error */
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EVARINT_OVERFLOW = -1,
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/* \brief Represents a non conical represnetation */
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EVARINT_REPRESENT = -2,
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};
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/*! \brief writes a varint to a stream.
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*/
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template<typename OutputIt, typename T>
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/* Requires T to be both an integral type and unsigned, should be a compile error if it is not */
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typename std::enable_if<std::is_integral<T>::value && std::is_unsigned<T>::value, void>::type
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write_varint(OutputIt &&dest, T i) {
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/* Make sure that there is one after this */
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while (i >= 0x80) {
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*dest = (static_cast<char>(i) & 0x7f) | 0x80;
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++dest;
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i >>= 7; /* I should be in multiples of 7, this should just get the next part */
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}
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/* writes the last one to dest */
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*dest = static_cast<char>(i);
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dest++; /* Seems kinda pointless... */
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}
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/*! \brief Returns the string that represents the varint
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*/
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template<typename T>
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std::string get_varint_data(const T& v)
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{
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std::stringstream ss;
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write_varint(std::ostreambuf_iterator<char>(ss), v);
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return ss.str();
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}
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/*! \brief reads in the varint that is pointed to by InputIt into write
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*/
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template<int bits, typename InputIt, typename T>
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typename std::enable_if<std::is_integral<T>::value && std::is_unsigned<T>::value && 0 <= bits && bits <= std::numeric_limits<T>::digits, int>::type
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read_varint(InputIt &&first, InputIt &&last, T &write) {
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int read = 0;
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write = 0;
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for (int shift = 0;; shift += 7) {
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if (first == last) {
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return read;
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}
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unsigned char byte = *first;
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++first;
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++read;
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if (shift + 7 >= bits && byte >= 1 << (bits - shift)) {
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return EVARINT_OVERFLOW;
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}
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if (byte == 0 && shift != 0) {
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return EVARINT_REPRESENT;
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}
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write |= static_cast<T>(byte & 0x7f) << shift; /* Does the actualy placing into write, stripping the first bit */
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/* If there is no next */
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if ((byte & 0x80) == 0) {
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break;
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}
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}
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return read;
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}
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/*! \brief Wrapper around the other read_varint,
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* Sets template parameters for you.
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*/
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template<typename InputIt, typename T>
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int read_varint(InputIt &&first, InputIt &&last, T &i) {
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return read_varint<std::numeric_limits<T>::digits, InputIt, T>(std::move(first), std::move(last), i);
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}
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}
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