359 lines
12 KiB
C
359 lines
12 KiB
C
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/*
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* Copyright 2004 The WebRTC 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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*/
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#ifndef WEBRTC_BASE_BUFFER_H_
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#define WEBRTC_BASE_BUFFER_H_
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#include <algorithm>
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#include <cstring>
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#include <memory>
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#include <type_traits>
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#include <utility>
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#include "webrtc/base/array_view.h"
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#include "webrtc/base/checks.h"
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namespace rtc {
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namespace internal {
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// (Internal; please don't use outside this file.) Determines if elements of
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// type U are compatible with a BufferT<T>. For most types, we just ignore
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// top-level const and forbid top-level volatile and require T and U to be
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// otherwise equal, but all byte-sized integers (notably char, int8_t, and
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// uint8_t) are compatible with each other. (Note: We aim to get rid of this
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// behavior, and treat all types the same.)
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template <typename T, typename U>
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struct BufferCompat {
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static constexpr bool value =
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!std::is_volatile<U>::value &&
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((std::is_integral<T>::value && sizeof(T) == 1)
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? (std::is_integral<U>::value && sizeof(U) == 1)
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: (std::is_same<T, typename std::remove_const<U>::type>::value));
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};
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} // namespace internal
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// Basic buffer class, can be grown and shrunk dynamically.
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// Unlike std::string/vector, does not initialize data when increasing size.
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template <typename T>
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class BufferT {
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// We want T's destructor and default constructor to be trivial, i.e. perform
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// no action, so that we don't have to touch the memory we allocate and
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// deallocate. And we want T to be trivially copyable, so that we can copy T
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// instances with std::memcpy. This is precisely the definition of a trivial
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// type.
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static_assert(std::is_trivial<T>::value, "T must be a trivial type.");
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// This class relies heavily on being able to mutate its data.
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static_assert(!std::is_const<T>::value, "T may not be const");
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public:
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// An empty BufferT.
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BufferT() : size_(0), capacity_(0), data_(nullptr) {
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RTC_DCHECK(IsConsistent());
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}
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// Disable copy construction and copy assignment, since copying a buffer is
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// expensive enough that we want to force the user to be explicit about it.
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BufferT(const BufferT&) = delete;
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BufferT& operator=(const BufferT&) = delete;
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BufferT(BufferT&& buf)
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: size_(buf.size()),
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capacity_(buf.capacity()),
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data_(std::move(buf.data_)) {
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RTC_DCHECK(IsConsistent());
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buf.OnMovedFrom();
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}
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// Construct a buffer with the specified number of uninitialized elements.
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explicit BufferT(size_t size) : BufferT(size, size) {}
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BufferT(size_t size, size_t capacity)
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: size_(size),
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capacity_(std::max(size, capacity)),
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data_(new T[capacity_]) {
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RTC_DCHECK(IsConsistent());
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}
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// Construct a buffer and copy the specified number of elements into it.
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template <typename U,
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typename std::enable_if<
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internal::BufferCompat<T, U>::value>::type* = nullptr>
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BufferT(const U* data, size_t size) : BufferT(data, size, size) {}
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template <typename U,
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typename std::enable_if<
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internal::BufferCompat<T, U>::value>::type* = nullptr>
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BufferT(U* data, size_t size, size_t capacity) : BufferT(size, capacity) {
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static_assert(sizeof(T) == sizeof(U), "");
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std::memcpy(data_.get(), data, size * sizeof(U));
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}
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// Construct a buffer from the contents of an array.
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template <typename U,
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size_t N,
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typename std::enable_if<
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internal::BufferCompat<T, U>::value>::type* = nullptr>
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BufferT(U (&array)[N]) : BufferT(array, N) {}
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// Get a pointer to the data. Just .data() will give you a (const) T*, but if
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// T is a byte-sized integer, you may also use .data<U>() for any other
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// byte-sized integer U.
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template <typename U = T,
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typename std::enable_if<
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internal::BufferCompat<T, U>::value>::type* = nullptr>
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const U* data() const {
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RTC_DCHECK(IsConsistent());
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return reinterpret_cast<U*>(data_.get());
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}
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template <typename U = T,
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typename std::enable_if<
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internal::BufferCompat<T, U>::value>::type* = nullptr>
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U* data() {
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RTC_DCHECK(IsConsistent());
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return reinterpret_cast<U*>(data_.get());
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}
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size_t size() const {
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RTC_DCHECK(IsConsistent());
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return size_;
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}
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size_t capacity() const {
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RTC_DCHECK(IsConsistent());
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return capacity_;
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}
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BufferT& operator=(BufferT&& buf) {
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RTC_DCHECK(IsConsistent());
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RTC_DCHECK(buf.IsConsistent());
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size_ = buf.size_;
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capacity_ = buf.capacity_;
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data_ = std::move(buf.data_);
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buf.OnMovedFrom();
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return *this;
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}
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bool operator==(const BufferT& buf) const {
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RTC_DCHECK(IsConsistent());
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if (size_ != buf.size_) {
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return false;
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}
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if (std::is_integral<T>::value) {
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// Optimization.
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return std::memcmp(data_.get(), buf.data_.get(), size_ * sizeof(T)) == 0;
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}
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for (size_t i = 0; i < size_; ++i) {
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if (data_[i] != buf.data_[i]) {
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return false;
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}
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}
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return true;
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}
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bool operator!=(const BufferT& buf) const { return !(*this == buf); }
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T& operator[](size_t index) {
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RTC_DCHECK_LT(index, size_);
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return data()[index];
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}
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T operator[](size_t index) const {
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RTC_DCHECK_LT(index, size_);
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return data()[index];
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}
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// The SetData functions replace the contents of the buffer. They accept the
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// same input types as the constructors.
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template <typename U,
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typename std::enable_if<
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internal::BufferCompat<T, U>::value>::type* = nullptr>
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void SetData(const U* data, size_t size) {
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RTC_DCHECK(IsConsistent());
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size_ = 0;
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AppendData(data, size);
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}
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template <typename U,
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size_t N,
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typename std::enable_if<
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internal::BufferCompat<T, U>::value>::type* = nullptr>
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void SetData(const U (&array)[N]) {
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SetData(array, N);
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}
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void SetData(const BufferT& buf) { SetData(buf.data(), buf.size()); }
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// Replace the data in the buffer with at most |max_elements| of data, using
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// the function |setter|, which should have the following signature:
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// size_t setter(ArrayView<U> view)
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// |setter| is given an appropriately typed ArrayView of the area in which to
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// write the data (i.e. starting at the beginning of the buffer) and should
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// return the number of elements actually written. This number must be <=
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// |max_elements|.
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template <typename U = T,
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typename F,
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typename std::enable_if<
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internal::BufferCompat<T, U>::value>::type* = nullptr>
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size_t SetData(size_t max_elements, F&& setter) {
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RTC_DCHECK(IsConsistent());
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size_ = 0;
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return AppendData<U>(max_elements, std::forward<F>(setter));
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}
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// The AppendData functions add data to the end of the buffer. They accept
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// the same input types as the constructors.
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template <typename U,
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typename std::enable_if<
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internal::BufferCompat<T, U>::value>::type* = nullptr>
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void AppendData(const U* data, size_t size) {
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RTC_DCHECK(IsConsistent());
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const size_t new_size = size_ + size;
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EnsureCapacityWithHeadroom(new_size, true);
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static_assert(sizeof(T) == sizeof(U), "");
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std::memcpy(data_.get() + size_, data, size * sizeof(U));
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size_ = new_size;
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RTC_DCHECK(IsConsistent());
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}
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template <typename U,
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size_t N,
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typename std::enable_if<
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internal::BufferCompat<T, U>::value>::type* = nullptr>
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void AppendData(const U (&array)[N]) {
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AppendData(array, N);
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}
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void AppendData(const BufferT& buf) { AppendData(buf.data(), buf.size()); }
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template <typename U,
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typename std::enable_if<
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internal::BufferCompat<T, U>::value>::type* = nullptr>
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void AppendData(const U& item) {
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AppendData(&item, 1);
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}
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// Append at most |max_elements| to the end of the buffer, using the function
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// |setter|, which should have the following signature:
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// size_t setter(ArrayView<U> view)
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// |setter| is given an appropriately typed ArrayView of the area in which to
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// write the data (i.e. starting at the former end of the buffer) and should
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// return the number of elements actually written. This number must be <=
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// |max_elements|.
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template <typename U = T,
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typename F,
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typename std::enable_if<
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internal::BufferCompat<T, U>::value>::type* = nullptr>
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size_t AppendData(size_t max_elements, F&& setter) {
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RTC_DCHECK(IsConsistent());
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const size_t old_size = size_;
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SetSize(old_size + max_elements);
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U* base_ptr = data<U>() + old_size;
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size_t written_elements = setter(rtc::ArrayView<U>(base_ptr, max_elements));
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RTC_CHECK_LE(written_elements, max_elements);
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size_ = old_size + written_elements;
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RTC_DCHECK(IsConsistent());
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return written_elements;
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}
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// Sets the size of the buffer. If the new size is smaller than the old, the
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// buffer contents will be kept but truncated; if the new size is greater,
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// the existing contents will be kept and the new space will be
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// uninitialized.
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void SetSize(size_t size) {
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EnsureCapacityWithHeadroom(size, true);
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size_ = size;
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}
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// Ensure that the buffer size can be increased to at least capacity without
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// further reallocation. (Of course, this operation might need to reallocate
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// the buffer.)
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void EnsureCapacity(size_t capacity) {
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// Don't allocate extra headroom, since the user is asking for a specific
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// capacity.
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EnsureCapacityWithHeadroom(capacity, false);
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}
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// Resets the buffer to zero size without altering capacity. Works even if the
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// buffer has been moved from.
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void Clear() {
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size_ = 0;
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RTC_DCHECK(IsConsistent());
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}
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// Swaps two buffers. Also works for buffers that have been moved from.
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friend void swap(BufferT& a, BufferT& b) {
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using std::swap;
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swap(a.size_, b.size_);
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swap(a.capacity_, b.capacity_);
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swap(a.data_, b.data_);
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}
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private:
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void EnsureCapacityWithHeadroom(size_t capacity, bool extra_headroom) {
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RTC_DCHECK(IsConsistent());
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if (capacity <= capacity_)
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return;
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// If the caller asks for extra headroom, ensure that the new capacity is
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// >= 1.5 times the old capacity. Any constant > 1 is sufficient to prevent
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// quadratic behavior; as to why we pick 1.5 in particular, see
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// https://github.com/facebook/folly/blob/master/folly/docs/FBVector.md and
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// http://www.gahcep.com/cpp-internals-stl-vector-part-1/.
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const size_t new_capacity =
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extra_headroom ? std::max(capacity, capacity_ + capacity_ / 2)
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: capacity;
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std::unique_ptr<T[]> new_data(new T[new_capacity]);
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std::memcpy(new_data.get(), data_.get(), size_ * sizeof(T));
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data_ = std::move(new_data);
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capacity_ = new_capacity;
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RTC_DCHECK(IsConsistent());
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}
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// Precondition for all methods except Clear and the destructor.
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// Postcondition for all methods except move construction and move
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// assignment, which leave the moved-from object in a possibly inconsistent
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// state.
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bool IsConsistent() const {
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return (data_ || capacity_ == 0) && capacity_ >= size_;
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}
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// Called when *this has been moved from. Conceptually it's a no-op, but we
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// can mutate the state slightly to help subsequent sanity checks catch bugs.
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void OnMovedFrom() {
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#ifdef NDEBUG
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// Make *this consistent and empty. Shouldn't be necessary, but better safe
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// than sorry.
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size_ = 0;
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capacity_ = 0;
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#else
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// Ensure that *this is always inconsistent, to provoke bugs.
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size_ = 1;
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capacity_ = 0;
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#endif
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}
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size_t size_;
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size_t capacity_;
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std::unique_ptr<T[]> data_;
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};
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// By far the most common sort of buffer.
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using Buffer = BufferT<uint8_t>;
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} // namespace rtc
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#endif // WEBRTC_BASE_BUFFER_H_
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