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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 <cassert>
#include <cstring>
#include <memory>
#include <vector>
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 mBlockSize;
};
typedef std::vector<Block>::const_iterator const_iterator;
/**
* Create a BigBuffer with block allocation sizes
* of blockSize.
*/
BigBuffer(size_t blockSize);
BigBuffer(const BigBuffer&) = delete; // No copying.
BigBuffer(BigBuffer&& rhs);
/**
* 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);
/**
* 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();
const_iterator begin() const;
const_iterator end() const;
private:
/**
* Returns a pointer to a buffer of the requested size.
* The buffer is zero-initialized.
*/
void* nextBlockImpl(size_t size);
size_t mBlockSize;
size_t mSize;
std::vector<Block> mBlocks;
};
inline BigBuffer::BigBuffer(size_t blockSize) : mBlockSize(blockSize), mSize(0) {
}
inline BigBuffer::BigBuffer(BigBuffer&& rhs) :
mBlockSize(rhs.mBlockSize), mSize(rhs.mSize), mBlocks(std::move(rhs.mBlocks)) {
}
inline size_t BigBuffer::size() const {
return mSize;
}
template <typename T>
inline T* BigBuffer::nextBlock(size_t count) {
assert(count != 0);
return reinterpret_cast<T*>(nextBlockImpl(sizeof(T) * count));
}
inline void BigBuffer::appendBuffer(BigBuffer&& buffer) {
std::move(buffer.mBlocks.begin(), buffer.mBlocks.end(), std::back_inserter(mBlocks));
mSize += buffer.mSize;
buffer.mBlocks.clear();
buffer.mSize = 0;
}
inline void BigBuffer::pad(size_t bytes) {
nextBlock<char>(bytes);
}
inline void BigBuffer::align4() {
const size_t unaligned = mSize % 4;
if (unaligned != 0) {
pad(4 - unaligned);
}
}
inline BigBuffer::const_iterator BigBuffer::begin() const {
return mBlocks.begin();
}
inline BigBuffer::const_iterator BigBuffer::end() const {
return mBlocks.end();
}
} // namespace aapt
#endif // AAPT_BIG_BUFFER_H
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