160 lines
3.8 KiB
C++
160 lines
3.8 KiB
C++
/*
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* Copyright (C) 2015 The Android Open Source Project
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*
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* Licensed under the Apache License, Version 2.0 (the "License");
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* you may not use this file except in compliance with the License.
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* You may obtain a copy of the License at
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*
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* http://www.apache.org/licenses/LICENSE-2.0
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*
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* Unless required by applicable law or agreed to in writing, software
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* distributed under the License is distributed on an "AS IS" BASIS,
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* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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* See the License for the specific language governing permissions and
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* limitations under the License.
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*/
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#ifndef AAPT_BIG_BUFFER_H
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#define AAPT_BIG_BUFFER_H
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#include <cassert>
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#include <cstring>
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#include <memory>
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#include <vector>
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namespace aapt {
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/**
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* Inspired by protobuf's ZeroCopyOutputStream, offers blocks of memory
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* in which to write without knowing the full size of the entire payload.
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* This is essentially a list of memory blocks. As one fills up, another
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* block is allocated and appended to the end of the list.
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*/
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class BigBuffer {
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public:
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/**
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* A contiguous block of allocated memory.
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*/
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struct Block {
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/**
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* Pointer to the memory.
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*/
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std::unique_ptr<uint8_t[]> buffer;
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/**
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* Size of memory that is currently occupied. The actual
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* allocation may be larger.
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*/
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size_t size;
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private:
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friend class BigBuffer;
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/**
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* The size of the memory block allocation.
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*/
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size_t mBlockSize;
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};
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typedef std::vector<Block>::const_iterator const_iterator;
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/**
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* Create a BigBuffer with block allocation sizes
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* of blockSize.
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*/
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BigBuffer(size_t blockSize);
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BigBuffer(const BigBuffer&) = delete; // No copying.
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BigBuffer(BigBuffer&& rhs);
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/**
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* Number of occupied bytes in all the allocated blocks.
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*/
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size_t size() const;
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/**
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* Returns a pointer to an array of T, where T is
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* a POD type. The elements are zero-initialized.
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*/
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template <typename T>
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T* nextBlock(size_t count = 1);
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/**
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* Moves the specified BigBuffer into this one. When this method
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* returns, buffer is empty.
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*/
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void appendBuffer(BigBuffer&& buffer);
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/**
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* Pads the block with 'bytes' bytes of zero values.
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*/
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void pad(size_t bytes);
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/**
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* Pads the block so that it aligns on a 4 byte boundary.
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*/
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void align4();
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const_iterator begin() const;
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const_iterator end() const;
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private:
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/**
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* Returns a pointer to a buffer of the requested size.
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* The buffer is zero-initialized.
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*/
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void* nextBlockImpl(size_t size);
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size_t mBlockSize;
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size_t mSize;
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std::vector<Block> mBlocks;
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};
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inline BigBuffer::BigBuffer(size_t blockSize) : mBlockSize(blockSize), mSize(0) {
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}
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inline BigBuffer::BigBuffer(BigBuffer&& rhs) :
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mBlockSize(rhs.mBlockSize), mSize(rhs.mSize), mBlocks(std::move(rhs.mBlocks)) {
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}
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inline size_t BigBuffer::size() const {
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return mSize;
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}
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template <typename T>
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inline T* BigBuffer::nextBlock(size_t count) {
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assert(count != 0);
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return reinterpret_cast<T*>(nextBlockImpl(sizeof(T) * count));
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}
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inline void BigBuffer::appendBuffer(BigBuffer&& buffer) {
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std::move(buffer.mBlocks.begin(), buffer.mBlocks.end(), std::back_inserter(mBlocks));
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mSize += buffer.mSize;
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buffer.mBlocks.clear();
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buffer.mSize = 0;
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}
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inline void BigBuffer::pad(size_t bytes) {
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nextBlock<char>(bytes);
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}
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inline void BigBuffer::align4() {
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const size_t unaligned = mSize % 4;
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if (unaligned != 0) {
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pad(4 - unaligned);
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}
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}
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inline BigBuffer::const_iterator BigBuffer::begin() const {
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return mBlocks.begin();
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}
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inline BigBuffer::const_iterator BigBuffer::end() const {
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return mBlocks.end();
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}
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} // namespace aapt
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#endif // AAPT_BIG_BUFFER_H
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