protozero: include/protozero/varint.hpp Source File

protozero 1.7.1 Minimalistic protocol buffer decoder and encoder in C++.

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varint.hpp
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1#ifndef PROTOZERO_VARINT_HPP
2#define PROTOZERO_VARINT_HPP
3
4/*****************************************************************************
5
6protozero - Minimalistic protocol buffer decoder and encoder in C++.
7
8This file is from https://github.com/mapbox/protozero where you can find more
9documentation.
10
11*****************************************************************************/
12
19#include "buffer_tmpl.hpp"
20#include "exception.hpp"
21
22#include <cstdint>
23
24namespace protozero {
25
29 constexpr const int8_t max_varint_length = sizeof(uint64_t) * 8 / 7 + 1;
30
31namespace detail {
32
33 // from https://github.com/facebook/folly/blob/master/folly/Varint.h
34 inline uint64_t decode_varint_impl(const char** data, const char* end) {
35 const auto* begin = reinterpret_cast<const int8_t*>(*data);
36 const auto* iend = reinterpret_cast<const int8_t*>(end);
37 const int8_t* p = begin;
38 uint64_t val = 0;
39
40 if (iend - begin >= max_varint_length) { // fast path
41 do {
42 int64_t b = *p++;
43 val = ((uint64_t(b) & 0x7fU) ); if (b >= 0) { break; }
44 b = *p++; val |= ((uint64_t(b) & 0x7fU) << 7U); if (b >= 0) { break; }
45 b = *p++; val |= ((uint64_t(b) & 0x7fU) << 14U); if (b >= 0) { break; }
46 b = *p++; val |= ((uint64_t(b) & 0x7fU) << 21U); if (b >= 0) { break; }
47 b = *p++; val |= ((uint64_t(b) & 0x7fU) << 28U); if (b >= 0) { break; }
48 b = *p++; val |= ((uint64_t(b) & 0x7fU) << 35U); if (b >= 0) { break; }
49 b = *p++; val |= ((uint64_t(b) & 0x7fU) << 42U); if (b >= 0) { break; }
50 b = *p++; val |= ((uint64_t(b) & 0x7fU) << 49U); if (b >= 0) { break; }
51 b = *p++; val |= ((uint64_t(b) & 0x7fU) << 56U); if (b >= 0) { break; }
52 b = *p++; val |= ((uint64_t(b) & 0x01U) << 63U); if (b >= 0) { break; }
53 throw varint_too_long_exception{};
54 } while (false);
55 } else {
56 unsigned int shift = 0;
57 while (p != iend && *p < 0) {
58 val |= (uint64_t(*p++) & 0x7fU) << shift;
59 shift += 7;
60 }
61 if (p == iend) {
62 throw end_of_buffer_exception{};
63 }
64 val |= uint64_t(*p++) << shift;
65 }
66
67 *data = reinterpret_cast<const char*>(p);
68 return val;
69 }
70
71} // end namespace detail
72
90 inline uint64_t decode_varint(const char** data, const char* end) {
91 // If this is a one-byte varint, decode it here.
92 if (end != *data && ((static_cast<uint64_t>(**data) & 0x80U) == 0)) {
93 const auto val = static_cast<uint64_t>(**data);
94 ++(*data);
95 return val;
96 }
97 // If this varint is more than one byte, defer to complete implementation.
98 return detail::decode_varint_impl(data, end);
99}
100
113 inline void skip_varint(const char** data, const char* end) {
114 const auto* begin = reinterpret_cast<const int8_t*>(*data);
115 const auto* iend = reinterpret_cast<const int8_t*>(end);
116 const int8_t* p = begin;
117
118 while (p != iend && *p < 0) {
119 ++p;
120 }
121
122 if (p - begin >= max_varint_length) {
123 throw varint_too_long_exception{};
124 }
125
126 if (p == iend) {
127 throw end_of_buffer_exception{};
128 }
129
130 ++p;
131
132 *data = reinterpret_cast<const char*>(p);
133}
134
146template <typename T>
147 inline int write_varint(T data, uint64_t value) {
148 int n = 1;
149
150 while (value >= 0x80U) {
151 *data++ = char((value & 0x7fU) | 0x80U);
152 value >>= 7U;
153 ++n;
154 }
155 *data = char(value);
156
157 return n;
158}
159
169template <typename TBuffer>
170 inline void add_varint_to_buffer(TBuffer* buffer, uint64_t value) {
171 while (value >= 0x80U) {
172 buffer_customization<TBuffer>::push_back(buffer, char((value & 0x7fU) | 0x80U));
173 value >>= 7U;
174 }
175 buffer_customization<TBuffer>::push_back(buffer, char(value));
176}
177
185 inline int add_varint_to_buffer(char* data, uint64_t value) noexcept {
186 int n = 1;
187
188 while (value >= 0x80U) {
189 *data++ = char((value & 0x7fU) | 0x80U);
190 value >>= 7U;
191 ++n;
192 }
193 *data = char(value);
194
195 return n;
196}
197
204 inline int length_of_varint(uint64_t value) noexcept {
205 int n = 1;
206
207 while (value >= 0x80U) {
208 value >>= 7U;
209 ++n;
210 }
211
212 return n;
213}
214
218 inline constexpr uint32_t encode_zigzag32(int32_t value) noexcept {
219 return (static_cast<uint32_t>(value) << 1U) ^ static_cast<uint32_t>(-static_cast<int32_t>(static_cast<uint32_t>(value) >> 31U));
220}
221
225 inline constexpr uint64_t encode_zigzag64(int64_t value) noexcept {
226 return (static_cast<uint64_t>(value) << 1U) ^ static_cast<uint64_t>(-static_cast<int64_t>(static_cast<uint64_t>(value) >> 63U));
227}
228
232 inline constexpr int32_t decode_zigzag32(uint32_t value) noexcept {
233 return static_cast<int32_t>((value >> 1U) ^ static_cast<uint32_t>(-static_cast<int32_t>(value & 1U)));
234}
235
239 inline constexpr int64_t decode_zigzag64(uint64_t value) noexcept {
240 return static_cast<int64_t>((value >> 1U) ^ static_cast<uint64_t>(-static_cast<int64_t>(value & 1U)));
241}
242
243} // end namespace protozero
244
245#endif // PROTOZERO_VARINT_HPP
buffer_tmpl.hpp
Contains the customization points for buffer implementations.
exception.hpp
Contains the exceptions used in the protozero library.
protozero
All parts of the protozero header-only library are in this namespace.
Definition basic_pbf_builder.hpp:24
protozero::decode_zigzag32
constexpr int32_t decode_zigzag32(uint32_t value) noexcept
Definition varint.hpp:232
protozero::add_varint_to_buffer
void add_varint_to_buffer(TBuffer *buffer, uint64_t value)
Definition varint.hpp:170
protozero::length_of_varint
int length_of_varint(uint64_t value) noexcept
Definition varint.hpp:204
protozero::encode_zigzag32
constexpr uint32_t encode_zigzag32(int32_t value) noexcept
Definition varint.hpp:218
protozero::decode_zigzag64
constexpr int64_t decode_zigzag64(uint64_t value) noexcept
Definition varint.hpp:239
protozero::encode_zigzag64
constexpr uint64_t encode_zigzag64(int64_t value) noexcept
Definition varint.hpp:225
protozero::max_varint_length
constexpr const int8_t max_varint_length
Definition varint.hpp:29
protozero::skip_varint
void skip_varint(const char **data, const char *end)
Definition varint.hpp:113
protozero::decode_varint
uint64_t decode_varint(const char **data, const char *end)
Definition varint.hpp:90
protozero::write_varint
int write_varint(T data, uint64_t value)
Definition varint.hpp:147
protozero::end_of_buffer_exception
Definition exception.hpp:67
protozero::varint_too_long_exception
Definition exception.hpp:41