/*
* 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
