blob: c6490fb2364f4915724e233116266ff941415eab (
plain)
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
|
// Copyright 2016 The Chromium Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
#include "components/base32/base32.h"
#include <stddef.h>
#include <algorithm>
#include <limits>
#include "base/logging.h"
namespace base32 {
namespace {
constexpr char kEncoding[] = "ABCDEFGHIJKLMNOPQRSTUVWXYZ234567";
} // namespace
std::string Base32Encode(base::StringPiece input, Base32EncodePolicy policy) {
if (input.empty())
return std::string();
if (input.size() > std::numeric_limits<size_t>::max() / 8) {
NOTREACHED()
<< "Input is too large and would overflow encoded size computation.";
return std::string();
}
// Per RFC4648, the output is formed of 8 characters per 40 bits of input and
// another 8 characters for the last group of [1,39] bits in the input.
// That is: ceil(input.size() * 8.0 / 40.0) * 8 ==
// ceil(input.size() / 5.0) * 8 ==
// ((input.size() + 4) / 5) * 8.
const size_t padded_length = ((input.size() + 4) / 5) * 8;
// When no padding is used, the output is exactly 1 character per 5 bits of
// input and one more for the last [1,4] bits.
// That is: ceil(input.size() * 8.0 / 5.0) ==
// (input.size() * 8 + 4) / 5.
const size_t unpadded_length = (input.size() * 8 + 4) / 5;
std::string output;
const size_t encoded_length = policy == Base32EncodePolicy::INCLUDE_PADDING
? padded_length
: unpadded_length;
output.reserve(encoded_length);
// A bit stream which will be read from the left and appended to from the
// right as it's emptied.
uint16_t bit_stream = (static_cast<uint8_t>(input[0]) << 8);
size_t next_byte_index = 1;
int free_bits = 8;
while (free_bits < 16) {
// Extract the 5 leftmost bits in the stream
output.push_back(kEncoding[(bit_stream & 0xf800) >> 11]);
bit_stream <<= 5;
free_bits += 5;
// If there is enough room in the bit stream, inject another byte (if there
// are any left...).
if (free_bits >= 8 && next_byte_index < input.size()) {
free_bits -= 8;
bit_stream += static_cast<uint8_t>(input[next_byte_index++]) << free_bits;
}
}
if (policy == Base32EncodePolicy::INCLUDE_PADDING) {
output.append(padded_length - unpadded_length, '=');
}
DCHECK_EQ(encoded_length, output.size());
return output;
}
} // namespace base32
|
