122 lines
3.9 KiB
C++
122 lines
3.9 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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#ifndef SRC_INT_PARSER_H_
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#define SRC_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 <type_traits>
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#include "src/element_parser.h"
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#include "src/parser_utils.h"
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#include "webm/callback.h"
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#include "webm/element.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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// Parses an EBML signed/unsigned int from a byte stream.
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// Spec reference:
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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#element-data-size
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// https://github.com/Matroska-Org/ebml-specification/blob/master/specification.markdown#ebml-element-types
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template <typename T>
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class IntParser : public ElementParser {
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public:
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static_assert(
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std::is_same<T, std::int64_t>::value ||
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std::is_same<T, std::uint64_t>::value ||
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(std::is_enum<T>::value && sizeof(T) == 8),
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"T must be either std::int64_t, std::uint64_t, or a 64-bit enum");
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// Constructs a new parser which will use the given default_value as the
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// value for the element if its size is zero. Defaults to the value zero (as
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// the EBML spec indicates).
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explicit IntParser(T default_value = {}) : default_value_(default_value) {}
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IntParser(IntParser&&) = default;
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IntParser& operator=(IntParser&&) = default;
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IntParser(const IntParser&) = delete;
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IntParser& operator=(const IntParser&) = delete;
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Status Init(const ElementMetadata& metadata,
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std::uint64_t max_size) override {
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assert(metadata.size == kUnknownElementSize || metadata.size <= max_size);
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// Matroska requires integers to be 0-8 bytes in size.
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if (metadata.size > 8) {
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return Status(Status::kInvalidElementSize);
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}
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size_ = num_bytes_remaining_ = static_cast<int>(metadata.size);
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if (metadata.size == 0) {
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value_ = default_value_;
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} else {
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value_ = {};
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}
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return Status(Status::kOkCompleted);
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}
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Status Feed(Callback* callback, Reader* reader,
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std::uint64_t* num_bytes_read) override {
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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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const Status status = AccumulateIntegerBytes(num_bytes_remaining_, reader,
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&value_, num_bytes_read);
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num_bytes_remaining_ -= static_cast<int>(*num_bytes_read);
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// Sign extend the integer if it's a negative value. EBML allows for
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// negative integers to drop superfluous sign bytes (i.e. -1 can be encoded
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// as 0xFF instead of 0xFFFFFFFFFFFFFFFF).
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if (std::is_signed<T>::value && num_bytes_remaining_ == 0 && size_ > 0) {
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std::uint64_t sign_bits = std::numeric_limits<std::uint64_t>::max()
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<< (8 * size_ - 1);
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std::uint64_t unsigned_value = static_cast<std::uint64_t>(value_);
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if (unsigned_value & sign_bits) {
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value_ = static_cast<T>(unsigned_value | sign_bits);
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}
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}
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return status;
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}
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// Gets the parsed int. This must not be called until the parse had been
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// successfully completed.
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T value() const {
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assert(num_bytes_remaining_ == 0);
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return value_;
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}
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// Gets the parsed int. This must not be called until the parse had been
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// successfully completed.
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T* mutable_value() {
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assert(num_bytes_remaining_ == 0);
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return &value_;
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}
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private:
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T value_;
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T default_value_;
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int num_bytes_remaining_ = -1;
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int size_;
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};
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using SignedIntParser = IntParser<std::int64_t>;
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using UnsignedIntParser = IntParser<std::uint64_t>;
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} // namespace webm
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#endif // SRC_INT_PARSER_H_
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