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/*
* Copyright (C) 2014 Max Kellermann <max.kellermann@gmail.com>
*
* 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 capacity;
const pointer_type data;
public:
constexpr CircularBuffer(pointer_type _data, size_type _capacity)
:head(0), tail(0), capacity(_capacity), data(_data) {}
CircularBuffer(const CircularBuffer &other) = delete;
protected:
constexpr size_type Next(size_type i) const {
return i + 1 == capacity
? 0
: i + 1;
}
public:
void Clear() {
head = tail = 0;
}
constexpr size_type GetCapacity() const {
return capacity;
}
constexpr bool empty() const {
return head == tail;
}
constexpr bool IsFull() const {
return Next(tail) == head;
}
/**
* Returns the number of elements stored in this buffer.
*/
constexpr size_type GetSize() const {
return head <= tail
? tail - head
: capacity - head + tail;
}
/**
* Returns the number of elements that can be added to this
* buffer.
*/
constexpr size_type GetSpace() const {
/* space = capacity - size - 1 */
return (head <= tail
? capacity - tail + head
: head - tail)
- 1;
}
/**
* Prepares writing. Returns a buffer range which may be written.
* When you are finished, call Append().
*/
Range Write() {
assert(head < capacity);
assert(tail < capacity);
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 */
: capacity - (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 < capacity);
assert(tail < capacity);
assert(n < capacity);
assert(tail + n <= capacity);
assert(head <= tail || tail + n < head);
tail += n;
if (tail == capacity) {
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 < capacity);
assert(tail < capacity);
return Range(data + head, (tail < head ? capacity : tail) - head);
}
/**
* Marks a chunk as consumed.
*/
void Consume(size_type n) {
assert(head < capacity);
assert(tail < capacity);
assert(n < capacity);
assert(head + n <= capacity);
assert(tail < head || head + n <= tail);
head += n;
if (head == capacity)
head = 0;
}
};
#endif
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