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/*
* Copyright (C) 2015 The Android Open Source Project
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
#ifndef AAPT_BIG_BUFFER_H
#define AAPT_BIG_BUFFER_H
#include <cstring>
#include <memory>
#include <string>
#include <type_traits>
#include <vector>
#include "android-base/logging.h"
#include "android-base/macros.h"
namespace aapt {
/**
* Inspired by protobuf's ZeroCopyOutputStream, offers blocks of memory
* in which to write without knowing the full size of the entire payload.
* This is essentially a list of memory blocks. As one fills up, another
* block is allocated and appended to the end of the list.
*/
class BigBuffer {
public:
/**
* A contiguous block of allocated memory.
*/
struct Block {
/**
* Pointer to the memory.
*/
std::unique_ptr<uint8_t[]> buffer;
/**
* Size of memory that is currently occupied. The actual
* allocation may be larger.
*/
size_t size;
private:
friend class BigBuffer;
/**
* The size of the memory block allocation.
*/
size_t block_size_;
};
typedef std::vector<Block>::const_iterator const_iterator;
/**
* Create a BigBuffer with block allocation sizes
* of block_size.
*/
explicit BigBuffer(size_t block_size);
BigBuffer(BigBuffer&& rhs) noexcept;
/**
* Number of occupied bytes in all the allocated blocks.
*/
size_t size() const;
/**
* Returns a pointer to an array of T, where T is
* a POD type. The elements are zero-initialized.
*/
template <typename T>
T* NextBlock(size_t count = 1);
/**
* Returns the next block available and puts the size in out_count.
* This is useful for grabbing blocks where the size doesn't matter.
* Use BackUp() to give back any bytes that were not used.
*/
void* NextBlock(size_t* out_count);
/**
* Backs up count bytes. This must only be called after NextBlock()
* and can not be larger than sizeof(T) * count of the last NextBlock()
* call.
*/
void BackUp(size_t count);
/**
* Moves the specified BigBuffer into this one. When this method
* returns, buffer is empty.
*/
void AppendBuffer(BigBuffer&& buffer);
/**
* Pads the block with 'bytes' bytes of zero values.
*/
void Pad(size_t bytes);
/**
* Pads the block so that it aligns on a 4 byte boundary.
*/
void Align4();
size_t block_size() const;
const_iterator begin() const;
const_iterator end() const;
std::string to_string() const;
private:
DISALLOW_COPY_AND_ASSIGN(BigBuffer);
/**
* Returns a pointer to a buffer of the requested size.
* The buffer is zero-initialized.
*/
void* NextBlockImpl(size_t size);
size_t block_size_;
size_t size_;
std::vector<Block> blocks_;
};
inline BigBuffer::BigBuffer(size_t block_size)
: block_size_(block_size), size_(0) {}
inline BigBuffer::BigBuffer(BigBuffer&& rhs) noexcept
: block_size_(rhs.block_size_),
size_(rhs.size_),
blocks_(std::move(rhs.blocks_)) {}
inline size_t BigBuffer::size() const { return size_; }
inline size_t BigBuffer::block_size() const { return block_size_; }
template <typename T>
inline T* BigBuffer::NextBlock(size_t count) {
static_assert(std::is_standard_layout<T>::value,
"T must be standard_layout type");
CHECK(count != 0);
return reinterpret_cast<T*>(NextBlockImpl(sizeof(T) * count));
}
inline void BigBuffer::BackUp(size_t count) {
Block& block = blocks_.back();
block.size -= count;
size_ -= count;
}
inline void BigBuffer::AppendBuffer(BigBuffer&& buffer) {
std::move(buffer.blocks_.begin(), buffer.blocks_.end(),
std::back_inserter(blocks_));
size_ += buffer.size_;
buffer.blocks_.clear();
buffer.size_ = 0;
}
inline void BigBuffer::Pad(size_t bytes) { NextBlock<char>(bytes); }
inline void BigBuffer::Align4() {
const size_t unaligned = size_ % 4;
if (unaligned != 0) {
Pad(4 - unaligned);
}
}
inline BigBuffer::const_iterator BigBuffer::begin() const {
return blocks_.begin();
}
inline BigBuffer::const_iterator BigBuffer::end() const {
return blocks_.end();
}
} // namespace aapt
#endif // AAPT_BIG_BUFFER_H
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