1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
|
// 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_
|
