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authorMax Kellermann <max@duempel.org>2014-03-15 17:30:08 +0100
committerMax Kellermann <max@duempel.org>2014-03-15 18:35:52 +0100
commitf660d30138e07afe81e6cbcedb1aab2a4fc36b41 (patch)
tree2513679ef9aa61a5d4c4fb53ef41aae575427b44 /src/util/CircularBuffer.hxx
parentb10276ff98ee11ebef112a5a04ee749c20902a97 (diff)
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util/CircularBuffer: new buffer class
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+/*
+ * Copyright (C) 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 CIRCULAR_BUFFER_HPP
+#define CIRCULAR_BUFFER_HPP
+
+#include "WritableBuffer.hxx"
+
+#include <assert.h>
+#include <stddef.h>
+
+/**
+ * A circular buffer.
+ *
+ * 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.
+ *
+ * Everything between #head and #tail is valid data (may wrap around).
+ * If both are equal, then the buffer is empty. Due to this
+ * implementation detail, the buffer is empty when #size-1 items are
+ * stored; the last buffer cell cannot be used.
+ */
+template<typename T>
+class CircularBuffer {
+public:
+ typedef WritableBuffer<T> Range;
+ typedef typename Range::pointer_type pointer_type;
+ typedef typename Range::size_type size_type;
+
+protected:
+ /**
+ * The next index to be read.
+ */
+ size_type head;
+
+ /**
+ * The next index to be written to.
+ */
+ size_type tail;
+
+ const size_type size;
+ const pointer_type data;
+
+public:
+ constexpr CircularBuffer(pointer_type _data, size_type _size)
+ :head(0), tail(0), size(_size), data(_data) {}
+
+ CircularBuffer(const CircularBuffer &other) = delete;
+
+protected:
+ constexpr size_type Next(size_type i) const {
+ return i + 1 == size
+ ? 0
+ : i + 1;
+ }
+
+public:
+ void Clear() {
+ head = tail = 0;
+ }
+
+ size_type GetSize() const {
+ return size;
+ }
+
+ constexpr bool IsEmpty() const {
+ return head == tail;
+ }
+
+ constexpr bool IsFull() const {
+ return Next(tail) == head;
+ }
+
+ /**
+ * Prepares writing. Returns a buffer range which may be written.
+ * When you are finished, call Append().
+ */
+ Range Write() {
+ assert(head < size);
+ assert(tail < size);
+
+ size_type end = tail < head
+ ? head - 1
+ /* the "head==0" is there so we don't write
+ the last cell, as this situation cannot be
+ represented by head/tail */
+ : size - (head == 0);
+
+ return Range(data + tail, end - tail);
+ }
+
+ /**
+ * Expands the tail of the buffer, after data has been written
+ * to the buffer returned by Write().
+ */
+ void Append(size_type n) {
+ assert(head < size);
+ assert(tail < size);
+ assert(n < size);
+ assert(tail + n <= size);
+ assert(head <= tail || tail + n < head);
+
+ tail += n;
+
+ if (tail == size) {
+ assert(head > 0);
+ tail = 0;
+ }
+ }
+
+ /**
+ * Return a buffer range which may be read. The buffer pointer is
+ * writable, to allow modifications while parsing.
+ */
+ Range Read() {
+ assert(head < size);
+ assert(tail < size);
+
+ return Range(data + head, (tail < head ? size : tail) - head);
+ }
+
+ /**
+ * Marks a chunk as consumed.
+ */
+ void Consume(size_type n) {
+ assert(head < size);
+ assert(tail < size);
+ assert(n < size);
+ assert(head + n <= size);
+ assert(tail < head || head + n <= tail);
+
+ head += n;
+ if (head == size)
+ head = 0;
+ }
+};
+
+#endif