1 // Copyright 2017 The Chromium 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.
4
5 #include "components/zucchini/buffer_source.h"
6
7 #include <algorithm>
8
9 #include "components/zucchini/algorithm.h"
10
11 namespace zucchini {
12
BufferSource(ConstBufferView buffer)13 BufferSource::BufferSource(ConstBufferView buffer) : ConstBufferView(buffer) {}
14
Skip(size_type n)15 BufferSource& BufferSource::Skip(size_type n) {
16 remove_prefix(std::min(n, Remaining()));
17 return *this;
18 }
19
CheckNextBytes(std::initializer_list<uint8_t> bytes) const20 bool BufferSource::CheckNextBytes(std::initializer_list<uint8_t> bytes) const {
21 if (Remaining() < bytes.size())
22 return false;
23 return std::mismatch(bytes.begin(), bytes.end(), begin()).first ==
24 bytes.end();
25 }
26
ConsumeBytes(std::initializer_list<uint8_t> bytes)27 bool BufferSource::ConsumeBytes(std::initializer_list<uint8_t> bytes) {
28 if (!CheckNextBytes(bytes))
29 return false;
30 remove_prefix(bytes.size());
31 return true;
32 }
33
GetRegion(size_type count,ConstBufferView * buffer)34 bool BufferSource::GetRegion(size_type count, ConstBufferView* buffer) {
35 DCHECK_NE(begin(), nullptr);
36 if (Remaining() < count)
37 return false;
38 *buffer = ConstBufferView(begin(), count);
39 remove_prefix(count);
40 return true;
41 }
42
43 // [0aaaaaaa] => 00000000'00000000'00000000'0aaaaaaa
44 // [1aaaaaaa 0bbbbbbb] => 00000000'00000000'00bbbbbb'baaaaaaa
45 // [1aaaaaaa 1bbbbbbb 0ccccccc] => 00000000'000ccccc'ccbbbbbb'baaaaaaa
46 // [1aaaaaaa 1bbbbbbb 1ccccccc 0ddddddd] => 0000dddd'dddccccc'ccbbbbbb'baaaaaaa
47 // [1aaaaaaa 1bbbbbbb 1ccccccc 1ddddddd 0???eeee]
48 // => eeeedddd'dddccccc'ccbbbbbb'baaaaaaa
49 // Note that "???" is discarded. Meanwhile, 1???eeee is invalid.
GetUleb128(uint32_t * ret)50 bool BufferSource::GetUleb128(uint32_t* ret) {
51 int shift_lim =
52 static_cast<int>(std::min<size_type>(kMaxLeb128Size, size())) * 7;
53 const_iterator cur = cbegin();
54 uint32_t value = 0U;
55 for (int shift = 0; shift < shift_lim; shift += 7, ++cur) {
56 uint32_t b = *cur;
57 // When |shift == 28|, |(b & 0x7F) << shift| discards the "???" bits.
58 value |= static_cast<uint32_t>(b & 0x7F) << shift;
59 if (!(b & 0x80)) {
60 *ret = value;
61 seek(cur + 1);
62 return true;
63 }
64 }
65 return false;
66 }
67
68 // [0Saaaaaa] => SSSSSSSS'SSSSSSSS'SSSSSSSS'SSaaaaaa
69 // [1aaaaaaa 0Sbbbbbb] => SSSSSSSS'SSSSSSSS'SSSbbbbb'baaaaaaa
70 // [1aaaaaaa 1bbbbbbb 0Scccccc] => SSSSSSSS'SSSScccc'ccbbbbbb'baaaaaaa
71 // [1aaaaaaa 1bbbbbbb 1ccccccc 0Sdddddd] => SSSSSddd'dddccccc'ccbbbbbb'baaaaaaa
72 // [1aaaaaaa 1bbbbbbb 1ccccccc 1ddddddd 0???Seee]
73 // => Seeedddd'dddccccc'ccbbbbbb'baaaaaaa
74 // Note that "???" is discarded. Meanwhile, 1???eeee is invalid.
GetSleb128(int32_t * ret)75 bool BufferSource::GetSleb128(int32_t* ret) {
76 int shift_lim =
77 static_cast<int>(std::min<size_type>(kMaxLeb128Size, size())) * 7;
78 const_iterator cur = cbegin();
79 int32_t value = 0;
80 for (int shift = 0; shift < shift_lim; shift += 7, ++cur) {
81 uint32_t b = *cur;
82 // When |shift == 28|, |(b & 0x7F) << shift| discards the "???" bits.
83 value |= static_cast<int32_t>(static_cast<uint32_t>(b & 0x7F) << shift);
84 if (!(b & 0x80)) {
85 *ret = (shift == 28) ? value : SignExtend(shift + 6, value);
86 seek(cur + 1);
87 return true;
88 }
89 }
90 return false;
91 }
92
SkipLeb128()93 bool BufferSource::SkipLeb128() {
94 int lim = static_cast<int>(std::min<size_type>(kMaxLeb128Size, size()));
95 const_iterator cur = cbegin();
96 for (int i = 0; i < lim; ++i, ++cur) {
97 if (!(*cur & 0x80)) {
98 seek(cur + 1);
99 return true;
100 }
101 }
102 return false;
103 }
104
105 } // namespace zucchini
106