Initial release

thirdparty/libwebm/webm_parser/include/webm/element.h

@@ -0,0 +1,208 @@
+// Copyright (c) 2016 The WebM project authors. All Rights Reserved.
+//
+// Use of this source code is governed by a BSD-style license
+// that can be found in the LICENSE file in the root of the source
+// tree. An additional intellectual property rights grant can be found
+// in the file PATENTS.  All contributing project authors may
+// be found in the AUTHORS file in the root of the source tree.
+#ifndef INCLUDE_WEBM_ELEMENT_H_
+#define INCLUDE_WEBM_ELEMENT_H_
+
+#include <cstdint>
+#include <limits>
+#include <utility>
+
+#include "./id.h"
+
+/**
+ \file
+ A wrapper around an object that represents a WebM element, including its parsed
+ metadata.
+ */
+
+namespace webm {
+
+/**
+ \addtogroup PUBLIC_API
+ @{
+ */
+
+/**
+ A wrapper around an object that represents a WebM element.
+
+ Since some elements may be absent, this wrapper is used to indicate the
+ presence (or lack thereof) of an element in a WebM document. If the element is
+ encoded in the file and it has been parsed, `is_present()` will return true.
+ Otherwise it will return false since the element was ommitted or skipped when
+ parsing.
+ */
+template <typename T>
+class Element {
+ public:
+  /**
+   Value-initializes the element's value and makes `is_present()` false.
+   */
+  constexpr Element() = default;
+
+  /**
+   Creates an element with the given value and makes `is_present()` false.
+
+   \param value The value of the element.
+   */
+  explicit constexpr Element(const T& value) : value_(value) {}
+
+  /**
+   Creates an element with the given value and makes `is_present()` false.
+
+   \param value The value of the element.
+   */
+  explicit constexpr Element(T&& value) : value_(std::move(value)) {}
+
+  /**
+   Creates an element with the given value and presence state.
+
+   \param value The value of the element.
+   \param is_present True if the element is present, false if it is absent.
+   */
+  constexpr Element(const T& value, bool is_present)
+      : value_(value), is_present_(is_present) {}
+
+  /**
+   Creates an element with the given value and presence state.
+
+   \param value The value of the element.
+   \param is_present True if the element is present, false if it is absent.
+   */
+  constexpr Element(T&& value, bool is_present)
+      : value_(std::move(value)), is_present_(is_present) {}
+
+  constexpr Element(const Element<T>& other) = default;
+  constexpr Element(Element<T>&& other) = default;
+
+  ~Element() = default;
+
+  Element<T>& operator=(const Element<T>& other) = default;
+  Element<T>& operator=(Element<T>&& other) = default;
+
+  /**
+   Sets the element's value and state.
+
+   \param value The new value for the element.
+   \param is_present The new presence state for the element.
+   */
+  void Set(const T& value, bool is_present) {
+    value_ = value;
+    is_present_ = is_present;
+  }
+
+  /**
+   Sets the element's value and state.
+
+   \param value The new value for the element.
+   \param is_present The new presence state for the element.
+   */
+  void Set(T&& value, bool is_present) {
+    value_ = std::move(value);
+    is_present_ = is_present;
+  }
+
+  /**
+   Gets the element's value.
+   */
+  constexpr const T& value() const { return value_; }
+
+  /**
+   Gets a mutuable pointer to the element's value (will never be null).
+   */
+  T* mutable_value() { return &value_; }
+
+  /**
+   Returns true if the element is present, false otherwise.
+   */
+  constexpr bool is_present() const { return is_present_; }
+
+  bool operator==(const Element<T>& other) const {
+    return is_present_ == other.is_present_ && value_ == other.value_;
+  }
+
+ private:
+  T value_{};
+  bool is_present_ = false;
+};
+
+/**
+ Metadata for WebM elements that are encountered when parsing.
+ */
+struct ElementMetadata {
+  /**
+   The EBML ID of the element.
+   */
+  Id id;
+
+  /**
+   The number of bytes that were used to encode the EBML ID and element size.
+
+   If the size of the header is unknown (which is only the case if a seek was
+   performed to the middle of an element, so its header was not parsed), this
+   will be the value `kUnknownHeaderSize`.
+   */
+  std::uint32_t header_size;
+
+  /**
+   The size of the element.
+
+   This is number of bytes in the element's body, which excludes the header
+   bytes.
+
+   If the size of the element's body is unknown, this will be the value
+   `kUnknownElementSize`.
+   */
+  std::uint64_t size;
+
+  /**
+   The absolute byte position of the element, starting at the first byte of the
+   element's header.
+
+   If the position of the element is unknown (which is only the case if a seek
+   was performed to the middle of an element), this will be the value
+   `kUnknownElementPosition`.
+   */
+  std::uint64_t position;
+
+  /**
+   Returns true if every member within the two objects are equal.
+   */
+  bool operator==(const ElementMetadata& other) const {
+    return id == other.id && header_size == other.header_size &&
+           size == other.size && position == other.position;
+  }
+};
+
+/**
+ A special value for `ElementMetadata::header_size` indicating the header size
+ is not known.
+ */
+constexpr std::uint64_t kUnknownHeaderSize =
+    std::numeric_limits<std::uint32_t>::max();
+
+/**
+ A special value for `ElementMetadata::size` indicating the element's size is
+ not known.
+ */
+constexpr std::uint64_t kUnknownElementSize =
+    std::numeric_limits<std::uint64_t>::max();
+
+/**
+ A special value for `ElementMetadata::position` indicating the element's
+ position is not known.
+ */
+constexpr std::uint64_t kUnknownElementPosition =
+    std::numeric_limits<std::uint64_t>::max();
+
+/**
+ @}
+ */
+
+}  // namespace webm
+
+#endif  // INCLUDE_WEBM_ELEMENT_H_