varint.hpp
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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.
*****************************************************************************/
#include <cstdint>
#include <protozero/exception.hpp>
namespace protozero {
const int8_t max_varint_length = sizeof(uint64_t) * 8 / 7 + 1;
// from https://github.com/facebook/folly/blob/master/folly/Varint.h
inline uint64_t decode_varint(const char** data, const char* end) {
const int8_t* begin = reinterpret_cast<const int8_t*>(*data);
const int8_t* 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;
b = *p++; val = uint64_t((b & 0x7f) ); if (b >= 0) break;
b = *p++; val |= uint64_t((b & 0x7f) << 7); if (b >= 0) break;
b = *p++; val |= uint64_t((b & 0x7f) << 14); if (b >= 0) break;
b = *p++; val |= uint64_t((b & 0x7f) << 21); if (b >= 0) break;
b = *p++; val |= uint64_t((b & 0x7f) << 28); if (b >= 0) break;
b = *p++; val |= uint64_t((b & 0x7f) << 35); if (b >= 0) break;
b = *p++; val |= uint64_t((b & 0x7f) << 42); if (b >= 0) break;
b = *p++; val |= uint64_t((b & 0x7f) << 49); if (b >= 0) break;
b = *p++; val |= uint64_t((b & 0x7f) << 56); if (b >= 0) break;
b = *p++; val |= uint64_t((b & 0x7f) << 63); if (b >= 0) break;
throw varint_too_long_exception();
} while (false);
} else {
int shift = 0;
while (p != iend && *p < 0) {
val |= uint64_t(*p++ & 0x7f) << shift;
shift += 7;
}
if (p == iend) {
throw end_of_buffer_exception();
}
val |= uint64_t(*p++) << shift;
}
*data = reinterpret_cast<const char*>(p);
return val;
}
template <typename OutputIterator>
inline int write_varint(OutputIterator data, uint64_t value) {
int n=1;
while (value >= 0x80) {
*data++ = char((value & 0x7f) | 0x80);
value >>= 7;
++n;
}
*data++ = char(value);
return n;
}
inline uint32_t encode_zigzag32(int32_t value) noexcept {
return (static_cast<uint32_t>(value) << 1) ^ (static_cast<uint32_t>(value >> 31));
}
inline uint64_t encode_zigzag64(int64_t value) noexcept {
return (static_cast<uint64_t>(value) << 1) ^ (static_cast<uint64_t>(value >> 63));
}
inline int32_t decode_zigzag32(uint32_t value) noexcept {
return int32_t(value >> 1) ^ -int32_t(value & 1);
}
inline int64_t decode_zigzag64(uint64_t value) noexcept {
return int64_t(value >> 1) ^ -int64_t(value & 1);
}
} // end namespace protozero
#endif // PROTOZERO_VARINT_HPP
protozero::encode_zigzag64
uint64_t encode_zigzag64(int64_t value) noexcept
Definition: varint.hpp:112
protozero::encode_zigzag32
uint32_t encode_zigzag32(int32_t value) noexcept
Definition: varint.hpp:105
protozero::max_varint_length
const int8_t max_varint_length
Definition: varint.hpp:28
exception.hpp
Contains the exceptions used in the protozero library.
protozero::write_varint
int write_varint(OutputIterator data, uint64_t value)
Definition: varint.hpp:89
protozero::varint_too_long_exception
Definition: exception.hpp:39
protozero::end_of_buffer_exception
Definition: exception.hpp:61
protozero::decode_varint
uint64_t decode_varint(const char **data, const char *end)
Definition: varint.hpp:48
protozero::decode_zigzag64
int64_t decode_zigzag64(uint64_t value) noexcept
Definition: varint.hpp:126
protozero
All parts of the protozero header-only library are in this namespace.
Definition: byteswap.hpp:24
protozero::decode_zigzag32
int32_t decode_zigzag32(uint32_t value) noexcept
Definition: varint.hpp:119