Inside Bitcoin

1// Copyright (c) 2011 The LevelDB Authors. All rights reserved.
2// Use of this source code is governed by a BSD-style license that can be
3// found in the LICENSE file. See the AUTHORS file for names of contributors.
4//
5// Endian-neutral encoding:
6// * Fixed-length numbers are encoded with least-significant byte first
7// * In addition we support variable length "varint" encoding
8// * Strings are encoded prefixed by their length in varint format
9
10#ifndef STORAGE_LEVELDB_UTIL_CODING_H_
11#define STORAGE_LEVELDB_UTIL_CODING_H_
12
13#include <cstdint>
14#include <cstring>
15#include <string>
16
17#include "leveldb/slice.h"
18#include "port/port.h"
19
20namespace leveldb {
21
22// Standard Put... routines append to a string
23void PutFixed32(std::string* dst, uint32_t value);
24void PutFixed64(std::string* dst, uint64_t value);
25void PutVarint32(std::string* dst, uint32_t value);
26void PutVarint64(std::string* dst, uint64_t value);
27void PutLengthPrefixedSlice(std::string* dst, const Slice& value);
28
29// Standard Get... routines parse a value from the beginning of a Slice
30// and advance the slice past the parsed value.
31bool GetVarint32(Slice* input, uint32_t* value);
32bool GetVarint64(Slice* input, uint64_t* value);
33bool GetLengthPrefixedSlice(Slice* input, Slice* result);
34
35// Pointer-based variants of GetVarint...  These either store a value
36// in *v and return a pointer just past the parsed value, or return
37// nullptr on error.  These routines only look at bytes in the range
38// [p..limit-1]
39const char* GetVarint32Ptr(const char* p, const char* limit, uint32_t* v);
40const char* GetVarint64Ptr(const char* p, const char* limit, uint64_t* v);
41
42// Returns the length of the varint32 or varint64 encoding of "v"
43int VarintLength(uint64_t v);
44
45// Lower-level versions of Put... that write directly into a character buffer
46// and return a pointer just past the last byte written.
47// REQUIRES: dst has enough space for the value being written
48char* EncodeVarint32(char* dst, uint32_t value);
49char* EncodeVarint64(char* dst, uint64_t value);
50
51// Lower-level versions of Put... that write directly into a character buffer
52// REQUIRES: dst has enough space for the value being written
53
54inline void EncodeFixed32(char* dst, uint32_t value) {
55  uint8_t* const buffer = reinterpret_cast<uint8_t*>(dst);
56
57  // Recent clang and gcc optimize this to a single mov / str instruction.
58  buffer[0] = static_cast<uint8_t>(value);
59  buffer[1] = static_cast<uint8_t>(value >> 8);
60  buffer[2] = static_cast<uint8_t>(value >> 16);
61  buffer[3] = static_cast<uint8_t>(value >> 24);
62}
63
64inline void EncodeFixed64(char* dst, uint64_t value) {
65  uint8_t* const buffer = reinterpret_cast<uint8_t*>(dst);
66
67  // Recent clang and gcc optimize this to a single mov / str instruction.
68  buffer[0] = static_cast<uint8_t>(value);
69  buffer[1] = static_cast<uint8_t>(value >> 8);
70  buffer[2] = static_cast<uint8_t>(value >> 16);
71  buffer[3] = static_cast<uint8_t>(value >> 24);
72  buffer[4] = static_cast<uint8_t>(value >> 32);
73  buffer[5] = static_cast<uint8_t>(value >> 40);
74  buffer[6] = static_cast<uint8_t>(value >> 48);
75  buffer[7] = static_cast<uint8_t>(value >> 56);
76}
77
78// Lower-level versions of Get... that read directly from a character buffer
79// without any bounds checking.
80
81inline uint32_t DecodeFixed32(const char* ptr) {
82  const uint8_t* const buffer = reinterpret_cast<const uint8_t*>(ptr);
83
84  // Recent clang and gcc optimize this to a single mov / ldr instruction.
85  return (static_cast<uint32_t>(buffer[0])) |
86         (static_cast<uint32_t>(buffer[1]) << 8) |
87         (static_cast<uint32_t>(buffer[2]) << 16) |
88         (static_cast<uint32_t>(buffer[3]) << 24);
89}
90
91inline uint64_t DecodeFixed64(const char* ptr) {
92  const uint8_t* const buffer = reinterpret_cast<const uint8_t*>(ptr);
93
94  // Recent clang and gcc optimize this to a single mov / ldr instruction.
95  return (static_cast<uint64_t>(buffer[0])) |
96         (static_cast<uint64_t>(buffer[1]) << 8) |
97         (static_cast<uint64_t>(buffer[2]) << 16) |
98         (static_cast<uint64_t>(buffer[3]) << 24) |
99         (static_cast<uint64_t>(buffer[4]) << 32) |
100         (static_cast<uint64_t>(buffer[5]) << 40) |
101         (static_cast<uint64_t>(buffer[6]) << 48) |
102         (static_cast<uint64_t>(buffer[7]) << 56);
103}
104
105// Internal routine for use by fallback path of GetVarint32Ptr
106const char* GetVarint32PtrFallback(const char* p, const char* limit,
107                                   uint32_t* value);
108inline const char* GetVarint32Ptr(const char* p, const char* limit,
109                                  uint32_t* value) {
110  if (p < limit) {
111    uint32_t result = *(reinterpret_cast<const uint8_t*>(p));
112    if ((result & 128) == 0) {
113      *value = result;
114      return p + 1;
115    }
116  }
117  return GetVarint32PtrFallback(p, limit, value);
118}
119
120}  // namespace leveldb
121
122#endif  // STORAGE_LEVELDB_UTIL_CODING_H_
123