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// Copyright 2017 The Chromium Authors
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
#ifdef UNSAFE_BUFFERS_BUILD
// TODO(crbug.com/40285824): Remove this and convert code to safer constructs.
#pragma allow_unsafe_buffers
#endif
#include "components/zucchini/buffer_source.h"
#include <algorithm>
#include "components/zucchini/algorithm.h"
namespace zucchini {
BufferSource::BufferSource(const ConstBufferView& buffer)
: ConstBufferView(buffer) {}
BufferSource::BufferSource(const ConstBufferView& buffer, size_type offset)
: ConstBufferView(buffer) {
Skip(offset);
}
bool BufferSource::Skip(size_type n) {
if (n > Remaining()) {
remove_prefix(Remaining());
return false;
}
remove_prefix(n);
return true;
}
bool BufferSource::CheckNextBytes(std::initializer_list<uint8_t> bytes) const {
if (Remaining() < bytes.size()) {
return false;
}
return std::ranges::mismatch(bytes, *this).in1 == bytes.end();
}
bool BufferSource::ConsumeBytes(std::initializer_list<uint8_t> bytes) {
if (!CheckNextBytes(bytes)) {
return false;
}
remove_prefix(bytes.size());
return true;
}
bool BufferSource::GetRegion(size_type count, ConstBufferView* buffer) {
DCHECK_NE(begin(), nullptr);
if (Remaining() < count) {
return false;
}
*buffer = ConstBufferView(begin(), count);
remove_prefix(count);
return true;
}
// [0aaaaaaa] => 00000000'00000000'00000000'0aaaaaaa
// [1aaaaaaa 0bbbbbbb] => 00000000'00000000'00bbbbbb'baaaaaaa
// [1aaaaaaa 1bbbbbbb 0ccccccc] => 00000000'000ccccc'ccbbbbbb'baaaaaaa
// [1aaaaaaa 1bbbbbbb 1ccccccc 0ddddddd] => 0000dddd'dddccccc'ccbbbbbb'baaaaaaa
// [1aaaaaaa 1bbbbbbb 1ccccccc 1ddddddd 0???eeee]
// => eeeedddd'dddccccc'ccbbbbbb'baaaaaaa
// Note that "???" is discarded. Meanwhile, 1???eeee is invalid.
bool BufferSource::GetUleb128(uint32_t* ret) {
int shift_lim =
static_cast<int>(std::min<size_type>(kMaxLeb128Size, size())) * 7;
const_iterator cur = cbegin();
uint32_t value = 0U;
for (int shift = 0; shift < shift_lim; shift += 7, ++cur) {
uint32_t b = *cur;
// When |shift == 28|, |(b & 0x7F) << shift| discards the "???" bits.
value |= static_cast<uint32_t>(b & 0x7F) << shift;
if (!(b & 0x80)) {
*ret = value;
seek(cur + 1);
return true;
}
}
return false;
}
// [0Saaaaaa] => SSSSSSSS'SSSSSSSS'SSSSSSSS'SSaaaaaa
// [1aaaaaaa 0Sbbbbbb] => SSSSSSSS'SSSSSSSS'SSSbbbbb'baaaaaaa
// [1aaaaaaa 1bbbbbbb 0Scccccc] => SSSSSSSS'SSSScccc'ccbbbbbb'baaaaaaa
// [1aaaaaaa 1bbbbbbb 1ccccccc 0Sdddddd] => SSSSSddd'dddccccc'ccbbbbbb'baaaaaaa
// [1aaaaaaa 1bbbbbbb 1ccccccc 1ddddddd 0???Seee]
// => Seeedddd'dddccccc'ccbbbbbb'baaaaaaa
// Note that "???" is discarded. Meanwhile, 1???eeee is invalid.
bool BufferSource::GetSleb128(int32_t* ret) {
int shift_lim =
static_cast<int>(std::min<size_type>(kMaxLeb128Size, size())) * 7;
const_iterator cur = cbegin();
int32_t value = 0;
for (int shift = 0; shift < shift_lim; shift += 7, ++cur) {
uint32_t b = *cur;
// When |shift == 28|, |(b & 0x7F) << shift| discards the "???" bits.
value |= static_cast<int32_t>(static_cast<uint32_t>(b & 0x7F) << shift);
if (!(b & 0x80)) {
*ret = (shift == 28) ? value : SignExtend(shift + 6, value);
seek(cur + 1);
return true;
}
}
return false;
}
bool BufferSource::SkipLeb128() {
int lim = static_cast<int>(std::min<size_type>(kMaxLeb128Size, size()));
const_iterator cur = cbegin();
for (int i = 0; i < lim; ++i, ++cur) {
if (!(*cur & 0x80)) {
seek(cur + 1);
return true;
}
}
return false;
}
} // namespace zucchini
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