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+/*
+ * Copyright (C) 2003-2014 Max Kellermann <max@duempel.org>
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ *
+ * - Redistributions of source code must retain the above copyright
+ * notice, this list of conditions and the following disclaimer.
+ *
+ * - Redistributions in binary form must reproduce the above copyright
+ * notice, this list of conditions and the following disclaimer in the
+ * documentation and/or other materials provided with the
+ * distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+ * ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+ * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
+ * FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
+ * FOUNDATION OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
+ * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
+ * (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
+ * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
+ * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT,
+ * STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
+ * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED
+ * OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+#ifndef FOREIGN_FIFO_BUFFER_HXX
+#define FOREIGN_FIFO_BUFFER_HXX
+
+#include "WritableBuffer.hxx"
+
+#include <utility>
+#include <algorithm>
+
+#include <cstddef>
+
+#include <assert.h>
+
+/**
+ * A first-in-first-out buffer: you can append data at the end, and
+ * read data from the beginning. This class automatically shifts the
+ * buffer as needed. It is not thread safe.
+ *
+ * This class does not manage buffer memory. It will not allocate or
+ * free any memory, it only manages the contents of an existing buffer
+ * given to the constructor.
+ */
+template<typename T>
+class ForeignFifoBuffer {
+public:
+ typedef size_t size_type;
+ typedef WritableBuffer<T> Range;
+ typedef typename Range::pointer_type pointer_type;
+ typedef typename Range::const_pointer_type const_pointer_type;
+
+protected:
+ size_type head, tail, capacity;
+ T *data;
+
+public:
+ explicit constexpr ForeignFifoBuffer(std::nullptr_t n)
+ :head(0), tail(0), capacity(0), data(n) {}
+
+ constexpr ForeignFifoBuffer(T *_data, size_type _capacity)
+ :head(0), tail(0), capacity(_capacity), data(_data) {}
+
+ ForeignFifoBuffer(ForeignFifoBuffer &&src)
+ :head(src.head), tail(src.tail),
+ capacity(src.capacity), data(src.data) {
+ src.SetNull();
+ }
+
+ ForeignFifoBuffer &operator=(ForeignFifoBuffer &&src) {
+ head = src.head;
+ tail = src.tail;
+ capacity = src.capacity;
+ data = src.data;
+ src.SetNull();
+ return *this;
+ }
+
+ void Swap(ForeignFifoBuffer<T> &other) {
+ std::swap(head, other.head);
+ std::swap(tail, other.tail);
+ std::swap(capacity, other.capacity);
+ std::swap(data, other.data);
+ }
+
+ constexpr bool IsNull() const {
+ return data == nullptr;
+ }
+
+ constexpr bool IsDefined() const {
+ return !IsNull();
+ }
+
+ T *GetBuffer() {
+ return data;
+ }
+
+ constexpr size_type GetCapacity() const {
+ return capacity;
+ }
+
+ void SetNull() {
+ head = tail = 0;
+ capacity = 0;
+ data = nullptr;
+ }
+
+ void SetBuffer(T *_data, size_type _capacity) {
+ assert(_data != nullptr);
+ assert(_capacity > 0);
+
+ head = tail = 0;
+ capacity = _capacity;
+ data = _data;
+ }
+
+ void MoveBuffer(T *new_data, size_type new_capacity) {
+ assert(new_capacity >= tail - head);
+
+ std::move(data + head, data + tail, new_data);
+ data = new_data;
+ capacity = new_capacity;
+ tail -= head;
+ head = 0;
+ }
+
+ void Clear() {
+ head = tail = 0;
+ }
+
+ constexpr bool IsEmpty() const {
+ return head == tail;
+ }
+
+ constexpr bool IsFull() const {
+ return head == 0 && tail == capacity;
+ }
+
+ /**
+ * Prepares writing. Returns a buffer range which may be written.
+ * When you are finished, call append().
+ */
+ Range Write() {
+ if (IsEmpty())
+ Clear();
+ else if (tail == capacity)
+ Shift();
+
+ return Range(data + tail, capacity - tail);
+ }
+
+ bool WantWrite(size_type n) {
+ if (tail + n <= capacity)
+ /* enough space after the tail */
+ return true;
+
+ const size_type in_use = tail - head;
+ const size_type required_capacity = in_use + n;
+ if (required_capacity > capacity)
+ return false;
+
+ Shift();
+ assert(tail + n <= capacity);
+ return true;
+ }
+
+ /**
+ * Expands the tail of the buffer, after data has been written to
+ * the buffer returned by write().
+ */
+ void Append(size_type n) {
+ assert(tail <= capacity);
+ assert(n <= capacity);
+ assert(tail + n <= capacity);
+
+ tail += n;
+ }
+
+ constexpr size_type GetAvailable() const {
+ return tail - head;
+ }
+
+ /**
+ * Return a buffer range which may be read. The buffer pointer is
+ * writable, to allow modifications while parsing.
+ */
+ constexpr Range Read() const {
+ return Range(data + head, tail - head);
+ }
+
+ /**
+ * Marks a chunk as consumed.
+ */
+ void Consume(size_type n) {
+ assert(tail <= capacity);
+ assert(head <= tail);
+ assert(n <= tail);
+ assert(head + n <= tail);
+
+ head += n;
+ }
+
+ size_type Read(pointer_type p, size_type n) {
+ auto range = Read();
+ if (n > range.size)
+ n = range.size;
+ std::copy_n(range.data, n, p);
+ Consume(n);
+ return n;
+ }
+
+ /**
+ * Move as much data as possible from the specified buffer.
+ *
+ * @return the number of items moved
+ */
+ size_type MoveFrom(ForeignFifoBuffer<T> &src) {
+ auto r = src.Read();
+ auto w = Write();
+ size_t n = std::min(r.size, w.size);
+
+ std::move(r.data, r.data + n, w.data);
+ Append(n);
+ src.Consume(n);
+ return n;
+ }
+
+protected:
+ void Shift() {
+ if (head == 0)
+ return;
+
+ assert(head <= capacity);
+ assert(tail <= capacity);
+ assert(tail >= head);
+
+ std::move(data + head, data + tail, data);
+
+ tail -= head;
+ head = 0;
+ }
+};
+
+#endif