Du kan inte välja fler än 25 ämnen
Ämnen måste starta med en bokstav eller siffra, kan innehålla bindestreck ('-') och vara max 35 tecken långa.
164 rader
6.2 KiB
164 rader
6.2 KiB
// Copyright (c) 2011 The LevelDB Authors. All rights reserved.
|
|
// Use of this source code is governed by a BSD-style license that can be
|
|
// found in the LICENSE file. See the AUTHORS file for names of contributors.
|
|
//
|
|
// Endian-neutral encoding:
|
|
// * Fixed-length numbers are encoded with least-significant byte first
|
|
// * In addition we support variable length "varint" encoding
|
|
// * Strings are encoded prefixed by their length in varint format
|
|
|
|
#ifndef STORAGE_LEVELDB_UTIL_CODING_H_
|
|
#define STORAGE_LEVELDB_UTIL_CODING_H_
|
|
|
|
#include <cstdint>
|
|
#include <cstring>
|
|
#include <string>
|
|
|
|
#include "leveldb/slice.h"
|
|
#include "port/port.h"
|
|
|
|
namespace leveldb {
|
|
|
|
// Standard Put... routines append to a string
|
|
void PutFixed32(std::string* dst, uint32_t value);
|
|
void PutFixed64(std::string* dst, uint64_t value);
|
|
void PutVarint32(std::string* dst, uint32_t value);
|
|
void PutVarint64(std::string* dst, uint64_t value);
|
|
void PutLengthPrefixedSlice(std::string* dst, const Slice& value);
|
|
|
|
// Standard Get... routines parse a value from the beginning of a Slice
|
|
// and advance the slice past the parsed value.
|
|
bool GetVarint32(Slice* input, uint32_t* value);
|
|
bool GetVarint64(Slice* input, uint64_t* value);
|
|
bool GetLengthPrefixedSlice(Slice* input, Slice* result);
|
|
|
|
// Pointer-based variants of GetVarint... These either store a value
|
|
// in *v and return a pointer just past the parsed value, or return
|
|
// nullptr on error. These routines only look at bytes in the range
|
|
// [p..limit-1]
|
|
const char* GetVarint32Ptr(const char* p, const char* limit, uint32_t* v);
|
|
const char* GetVarint64Ptr(const char* p, const char* limit, uint64_t* v);
|
|
|
|
// Returns the length of the varint32 or varint64 encoding of "v"
|
|
int VarintLength(uint64_t v);
|
|
|
|
// Lower-level versions of Put... that write directly into a character buffer
|
|
// and return a pointer just past the last byte written.
|
|
// REQUIRES: dst has enough space for the value being written
|
|
char* EncodeVarint32(char* dst, uint32_t value);
|
|
char* EncodeVarint64(char* dst, uint64_t value);
|
|
|
|
// TODO(costan): Remove port::kLittleEndian and the fast paths based on
|
|
// std::memcpy when clang learns to optimize the generic code, as
|
|
// described in https://bugs.llvm.org/show_bug.cgi?id=41761
|
|
//
|
|
// The platform-independent code in DecodeFixed{32,64}() gets optimized to mov
|
|
// on x86 and ldr on ARM64, by both clang and gcc. However, only gcc optimizes
|
|
// the platform-independent code in EncodeFixed{32,64}() to mov / str.
|
|
|
|
// Lower-level versions of Put... that write directly into a character buffer
|
|
// REQUIRES: dst has enough space for the value being written
|
|
|
|
inline void EncodeFixed32(char* dst, uint32_t value) {
|
|
uint8_t* const buffer = reinterpret_cast<uint8_t*>(dst);
|
|
|
|
if (port::kLittleEndian) {
|
|
// Fast path for little-endian CPUs. All major compilers optimize this to a
|
|
// single mov (x86_64) / str (ARM) instruction.
|
|
std::memcpy(buffer, &value, sizeof(uint32_t));
|
|
return;
|
|
}
|
|
|
|
// Platform-independent code.
|
|
// Currently, only gcc optimizes this to a single mov / str instruction.
|
|
buffer[0] = static_cast<uint8_t>(value);
|
|
buffer[1] = static_cast<uint8_t>(value >> 8);
|
|
buffer[2] = static_cast<uint8_t>(value >> 16);
|
|
buffer[3] = static_cast<uint8_t>(value >> 24);
|
|
}
|
|
|
|
inline void EncodeFixed64(char* dst, uint64_t value) {
|
|
uint8_t* const buffer = reinterpret_cast<uint8_t*>(dst);
|
|
|
|
if (port::kLittleEndian) {
|
|
// Fast path for little-endian CPUs. All major compilers optimize this to a
|
|
// single mov (x86_64) / str (ARM) instruction.
|
|
std::memcpy(buffer, &value, sizeof(uint64_t));
|
|
return;
|
|
}
|
|
|
|
// Platform-independent code.
|
|
// Currently, only gcc optimizes this to a single mov / str instruction.
|
|
buffer[0] = static_cast<uint8_t>(value);
|
|
buffer[1] = static_cast<uint8_t>(value >> 8);
|
|
buffer[2] = static_cast<uint8_t>(value >> 16);
|
|
buffer[3] = static_cast<uint8_t>(value >> 24);
|
|
buffer[4] = static_cast<uint8_t>(value >> 32);
|
|
buffer[5] = static_cast<uint8_t>(value >> 40);
|
|
buffer[6] = static_cast<uint8_t>(value >> 48);
|
|
buffer[7] = static_cast<uint8_t>(value >> 56);
|
|
}
|
|
|
|
// Lower-level versions of Get... that read directly from a character buffer
|
|
// without any bounds checking.
|
|
|
|
inline uint32_t DecodeFixed32(const char* ptr) {
|
|
const uint8_t* const buffer = reinterpret_cast<const uint8_t*>(ptr);
|
|
|
|
if (port::kLittleEndian) {
|
|
// Fast path for little-endian CPUs. All major compilers optimize this to a
|
|
// single mov (x86_64) / ldr (ARM) instruction.
|
|
uint32_t result;
|
|
std::memcpy(&result, buffer, sizeof(uint32_t));
|
|
return result;
|
|
}
|
|
|
|
// Platform-independent code.
|
|
// Clang and gcc optimize this to a single mov / ldr instruction.
|
|
return (static_cast<uint32_t>(buffer[0])) |
|
|
(static_cast<uint32_t>(buffer[1]) << 8) |
|
|
(static_cast<uint32_t>(buffer[2]) << 16) |
|
|
(static_cast<uint32_t>(buffer[3]) << 24);
|
|
}
|
|
|
|
inline uint64_t DecodeFixed64(const char* ptr) {
|
|
const uint8_t* const buffer = reinterpret_cast<const uint8_t*>(ptr);
|
|
|
|
if (port::kLittleEndian) {
|
|
// Fast path for little-endian CPUs. All major compilers optimize this to a
|
|
// single mov (x86_64) / ldr (ARM) instruction.
|
|
uint64_t result;
|
|
std::memcpy(&result, buffer, sizeof(uint64_t));
|
|
return result;
|
|
}
|
|
|
|
// Platform-independent code.
|
|
// Clang and gcc optimize this to a single mov / ldr instruction.
|
|
return (static_cast<uint64_t>(buffer[0])) |
|
|
(static_cast<uint64_t>(buffer[1]) << 8) |
|
|
(static_cast<uint64_t>(buffer[2]) << 16) |
|
|
(static_cast<uint64_t>(buffer[3]) << 24) |
|
|
(static_cast<uint64_t>(buffer[4]) << 32) |
|
|
(static_cast<uint64_t>(buffer[5]) << 40) |
|
|
(static_cast<uint64_t>(buffer[6]) << 48) |
|
|
(static_cast<uint64_t>(buffer[7]) << 56);
|
|
}
|
|
|
|
// Internal routine for use by fallback path of GetVarint32Ptr
|
|
const char* GetVarint32PtrFallback(const char* p, const char* limit,
|
|
uint32_t* value);
|
|
inline const char* GetVarint32Ptr(const char* p, const char* limit,
|
|
uint32_t* value) {
|
|
if (p < limit) {
|
|
uint32_t result = *(reinterpret_cast<const uint8_t*>(p));
|
|
if ((result & 128) == 0) {
|
|
*value = result;
|
|
return p + 1;
|
|
}
|
|
}
|
|
return GetVarint32PtrFallback(p, limit, value);
|
|
}
|
|
|
|
} // namespace leveldb
|
|
|
|
#endif // STORAGE_LEVELDB_UTIL_CODING_H_
|