72 lines
2.2 KiB
C++
72 lines
2.2 KiB
C++
// Copyright (c) 2016 The WebM project authors. All Rights Reserved.
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//
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// Use of this source code is governed by a BSD-style license
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// that can be found in the LICENSE file in the root of the source
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// tree. An additional intellectual property rights grant can be found
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// in the file PATENTS. All contributing project authors may
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// be found in the AUTHORS file in the root of the source tree.
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#include "src/var_int_parser.h"
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#include <cassert>
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#include <cstdint>
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#include <limits>
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#include "src/bit_utils.h"
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#include "src/parser_utils.h"
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#include "webm/reader.h"
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#include "webm/status.h"
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namespace webm {
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// Spec references:
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// http://matroska.org/technical/specs/index.html#EBML_ex
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// https://github.com/Matroska-Org/ebml-specification/blob/master/specification.markdown#variable-size-integer
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Status VarIntParser::Feed(Callback* callback, Reader* reader,
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std::uint64_t* num_bytes_read) {
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assert(callback != nullptr);
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assert(reader != nullptr);
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assert(num_bytes_read != nullptr);
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assert(num_bytes_remaining_ != 0);
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*num_bytes_read = 0;
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if (num_bytes_remaining_ == -1) {
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std::uint8_t first_byte;
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const Status status = ReadByte(reader, &first_byte);
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if (!status.completed_ok()) {
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return status;
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}
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++*num_bytes_read;
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// The first byte must have a marker bit set to indicate how many octets are
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// used.
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if (first_byte == 0) {
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return Status(Status::kInvalidElementValue);
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}
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total_data_bytes_ = CountLeadingZeros(first_byte);
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num_bytes_remaining_ = total_data_bytes_;
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value_ = first_byte;
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}
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std::uint64_t local_num_bytes_read;
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const Status status = AccumulateIntegerBytes(num_bytes_remaining_, reader,
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&value_, &local_num_bytes_read);
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*num_bytes_read += local_num_bytes_read;
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num_bytes_remaining_ -= static_cast<int>(local_num_bytes_read);
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if (!status.completed_ok()) {
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return status;
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}
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// Clear the marker bit.
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constexpr std::uint64_t all_bits = std::numeric_limits<std::uint64_t>::max();
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const std::uint64_t data_bits = all_bits >> (57 - 7 * total_data_bytes_);
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value_ &= data_bits;
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return Status(Status::kOkCompleted);
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}
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} // namespace webm
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