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#ifndef PROTOZERO_VARINT_HPP
#define PROTOZERO_VARINT_HPP
/*****************************************************************************
protozero - Minimalistic protocol buffer decoder and encoder in C++.
This file is from https://github.com/mapbox/protozero where you can find more
documentation.
*****************************************************************************/
/**
* @file varint.hpp
*
* @brief Contains low-level varint and zigzag encoding and decoding functions.
*/
#include "buffer_tmpl.hpp"
#include "exception.hpp"
#include <cstdint>
namespace protozero {
/**
* The maximum length of a 64 bit varint.
*/
constexpr const int8_t max_varint_length = sizeof(uint64_t) * 8 / 7 + 1;
namespace detail {
// from https://github.com/facebook/folly/blob/master/folly/Varint.h
inline uint64_t decode_varint_impl(const char** data, const char* end) {
const auto* begin = reinterpret_cast<const int8_t*>(*data);
const auto* iend = reinterpret_cast<const int8_t*>(end);
const int8_t* p = begin;
uint64_t val = 0;
if (iend - begin >= max_varint_length) { // fast path
do {
int64_t b = *p++;
val = ((uint64_t(b) & 0x7fU) ); if (b >= 0) { break; }
b = *p++; val |= ((uint64_t(b) & 0x7fU) << 7U); if (b >= 0) { break; }
b = *p++; val |= ((uint64_t(b) & 0x7fU) << 14U); if (b >= 0) { break; }
b = *p++; val |= ((uint64_t(b) & 0x7fU) << 21U); if (b >= 0) { break; }
b = *p++; val |= ((uint64_t(b) & 0x7fU) << 28U); if (b >= 0) { break; }
b = *p++; val |= ((uint64_t(b) & 0x7fU) << 35U); if (b >= 0) { break; }
b = *p++; val |= ((uint64_t(b) & 0x7fU) << 42U); if (b >= 0) { break; }
b = *p++; val |= ((uint64_t(b) & 0x7fU) << 49U); if (b >= 0) { break; }
b = *p++; val |= ((uint64_t(b) & 0x7fU) << 56U); if (b >= 0) { break; }
b = *p++; val |= ((uint64_t(b) & 0x01U) << 63U); if (b >= 0) { break; }
throw varint_too_long_exception{};
} while (false);
} else {
unsigned int shift = 0;
while (p != iend && *p < 0) {
val |= (uint64_t(*p++) & 0x7fU) << shift;
shift += 7;
}
if (p == iend) {
throw end_of_buffer_exception{};
}
val |= uint64_t(*p++) << shift;
}
*data = reinterpret_cast<const char*>(p);
return val;
}
} // end namespace detail
/**
* Decode a 64 bit varint.
*
* Strong exception guarantee: if there is an exception the data pointer will
* not be changed.
*
* @param[in,out] data Pointer to pointer to the input data. After the function
* returns this will point to the next data to be read.
* @param[in] end Pointer one past the end of the input data.
* @returns The decoded integer
* @throws varint_too_long_exception if the varint is longer then the maximum
* length that would fit in a 64 bit int. Usually this means your data
* is corrupted or you are trying to read something as a varint that
* isn't.
* @throws end_of_buffer_exception if the *end* of the buffer was reached
* before the end of the varint.
*/
inline uint64_t decode_varint(const char** data, const char* end) {
// If this is a one-byte varint, decode it here.
if (end != *data && ((static_cast<uint64_t>(**data) & 0x80U) == 0)) {
const auto val = static_cast<uint64_t>(**data);
++(*data);
return val;
}
// If this varint is more than one byte, defer to complete implementation.
return detail::decode_varint_impl(data, end);
}
/**
* Skip over a varint.
*
* Strong exception guarantee: if there is an exception the data pointer will
* not be changed.
*
* @param[in,out] data Pointer to pointer to the input data. After the function
* returns this will point to the next data to be read.
* @param[in] end Pointer one past the end of the input data.
* @throws end_of_buffer_exception if the *end* of the buffer was reached
* before the end of the varint.
*/
inline void skip_varint(const char** data, const char* end) {
const auto* begin = reinterpret_cast<const int8_t*>(*data);
const auto* iend = reinterpret_cast<const int8_t*>(end);
const int8_t* p = begin;
while (p != iend && *p < 0) {
++p;
}
if (p - begin >= max_varint_length) {
throw varint_too_long_exception{};
}
if (p == iend) {
throw end_of_buffer_exception{};
}
++p;
*data = reinterpret_cast<const char*>(p);
}
/**
* Varint encode a 64 bit integer.
*
* @tparam T An output iterator type.
* @param data Output iterator the varint encoded value will be written to
* byte by byte.
* @param value The integer that will be encoded.
* @returns the number of bytes written
* @throws Any exception thrown by increment or dereference operator on data.
* @deprecated Use add_varint_to_buffer() instead.
*/
template <typename T>
inline int write_varint(T data, uint64_t value) {
int n = 1;
while (value >= 0x80U) {
*data++ = char((value & 0x7fU) | 0x80U);
value >>= 7U;
++n;
}
*data = char(value);
return n;
}
/**
* Varint encode a 64 bit integer.
*
* @tparam TBuffer A buffer type.
* @param buffer Output buffer the varint will be written to.
* @param value The integer that will be encoded.
* @returns the number of bytes written
* @throws Any exception thrown by calling the buffer_push_back() function.
*/
template <typename TBuffer>
inline void add_varint_to_buffer(TBuffer* buffer, uint64_t value) {
while (value >= 0x80U) {
buffer_customization<TBuffer>::push_back(buffer, char((value & 0x7fU) | 0x80U));
value >>= 7U;
}
buffer_customization<TBuffer>::push_back(buffer, char(value));
}
/**
* Varint encode a 64 bit integer.
*
* @param data Where to add the varint. There must be enough space available!
* @param value The integer that will be encoded.
* @returns the number of bytes written
*/
inline int add_varint_to_buffer(char* data, uint64_t value) noexcept {
int n = 1;
while (value >= 0x80U) {
*data++ = char((value & 0x7fU) | 0x80U);
value >>= 7U;
++n;
}
*data = char(value);
return n;
}
/**
* Get the length of the varint the specified value would produce.
*
* @param value The integer to be encoded.
* @returns the number of bytes the varint would have if we created it.
*/
inline int length_of_varint(uint64_t value) noexcept {
int n = 1;
while (value >= 0x80U) {
value >>= 7U;
++n;
}
return n;
}
/**
* ZigZag encodes a 32 bit integer.
*/
inline constexpr uint32_t encode_zigzag32(int32_t value) noexcept {
return (static_cast<uint32_t>(value) << 1U) ^ static_cast<uint32_t>(-static_cast<int32_t>(static_cast<uint32_t>(value) >> 31U));
}
/**
* ZigZag encodes a 64 bit integer.
*/
inline constexpr uint64_t encode_zigzag64(int64_t value) noexcept {
return (static_cast<uint64_t>(value) << 1U) ^ static_cast<uint64_t>(-static_cast<int64_t>(static_cast<uint64_t>(value) >> 63U));
}
/**
* Decodes a 32 bit ZigZag-encoded integer.
*/
inline constexpr int32_t decode_zigzag32(uint32_t value) noexcept {
return static_cast<int32_t>((value >> 1U) ^ static_cast<uint32_t>(-static_cast<int32_t>(value & 1U)));
}
/**
* Decodes a 64 bit ZigZag-encoded integer.
*/
inline constexpr int64_t decode_zigzag64(uint64_t value) noexcept {
return static_cast<int64_t>((value >> 1U) ^ static_cast<uint64_t>(-static_cast<int64_t>(value & 1U)));
}
} // end namespace protozero
#endif // PROTOZERO_VARINT_HPP
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