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
|
// Copyright 2020 The Pigweed Authors
//
// Licensed under the Apache License, Version 2.0 (the "License"); you may not
// use this file except in compliance with the License. You may obtain a copy of
// the License at
//
// https://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
// WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
// License for the specific language governing permissions and limitations under
// the License.
#include "pw_varint/varint.h"
#include <algorithm>
#include <cstddef>
namespace pw {
namespace varint {
namespace {
inline bool ZeroTerminated(pw_varint_Format format) {
return (static_cast<unsigned>(format) & 0b10) == 0;
}
inline bool LeastSignificant(pw_varint_Format format) {
return (static_cast<unsigned>(format) & 0b01) == 0;
}
} // namespace
extern "C" size_t pw_varint_EncodeCustom(uint64_t integer,
void* output,
size_t output_size,
pw_varint_Format format) {
size_t written = 0;
std::byte* buffer = static_cast<std::byte*>(output);
int value_shift = LeastSignificant(format) ? 1 : 0;
int term_shift = value_shift == 1 ? 0 : 7;
std::byte cont, term;
if (ZeroTerminated(format)) {
cont = std::byte(0x01) << term_shift;
term = std::byte(0x00) << term_shift;
} else {
cont = std::byte(0x00) << term_shift;
term = std::byte(0x01) << term_shift;
}
do {
if (written >= output_size) {
return 0;
}
bool last_byte = (integer >> 7) == 0u;
// Grab 7 bits and set the eighth according to the continuation bit.
std::byte value = (static_cast<std::byte>(integer) & std::byte(0x7f))
<< value_shift;
if (last_byte) {
value |= term;
} else {
value |= cont;
}
buffer[written++] = value;
integer >>= 7;
} while (integer != 0u);
return written;
}
extern "C" size_t pw_varint_DecodeCustom(const void* input,
size_t input_size,
uint64_t* output,
pw_varint_Format format) {
uint64_t decoded_value = 0;
uint_fast8_t count = 0;
const std::byte* buffer = static_cast<const std::byte*>(input);
// The largest 64-bit ints require 10 B.
const size_t max_count = std::min(kMaxVarint64SizeBytes, input_size);
std::byte mask;
uint32_t shift;
if (LeastSignificant(format)) {
mask = std::byte(0xfe);
shift = 1;
} else {
mask = std::byte(0x7f);
shift = 0;
}
// Determines whether a byte is the last byte of a varint.
auto is_last_byte = [&](std::byte byte) {
if (ZeroTerminated(format)) {
return (byte & ~mask) == std::byte(0);
}
return (byte & ~mask) != std::byte(0);
};
while (true) {
if (count >= max_count) {
return 0;
}
// Add the bottom seven bits of the next byte to the result.
decoded_value |= static_cast<uint64_t>((buffer[count] & mask) >> shift)
<< (7 * count);
// Stop decoding if the end is reached.
if (is_last_byte(buffer[count++])) {
break;
}
}
*output = decoded_value;
return count;
}
// TODO(frolv): Remove this deprecated alias.
extern "C" size_t pw_VarintEncode(uint64_t integer,
void* output,
size_t output_size) {
return pw_varint_Encode(integer, output, output_size);
}
extern "C" size_t pw_varint_ZigZagEncode(int64_t integer,
void* output,
size_t output_size) {
return pw_varint_Encode(ZigZagEncode(integer), output, output_size);
}
// TODO(frolv): Remove this deprecated alias.
extern "C" size_t pw_VarintDecode(const void* input,
size_t input_size,
uint64_t* output) {
return pw_varint_Decode(input, input_size, output);
}
extern "C" size_t pw_varint_ZigZagDecode(const void* input,
size_t input_size,
int64_t* output) {
uint64_t value = 0;
size_t bytes = pw_varint_Decode(input, input_size, &value);
*output = ZigZagDecode(value);
return bytes;
}
extern "C" size_t pw_varint_EncodedSize(uint64_t integer) {
return EncodedSize(integer);
}
extern "C" size_t pw_varint_ZigZagEncodedSize(int64_t integer) {
return ZigZagEncodedSize(integer);
}
} // namespace varint
} // namespace pw
|
