272 lines
10 KiB
C
272 lines
10 KiB
C
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// Tencent is pleased to support the open source community by making RapidJSON available.
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//
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// Copyright (C) 2015 THL A29 Limited, a Tencent company, and Milo Yip. All rights reserved.
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//
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// Licensed under the MIT License (the "License"); you may not use this file except
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// in compliance with the License. You may obtain a copy of the License at
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//
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// http://opensource.org/licenses/MIT
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//
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// Unless required by applicable law or agreed to in writing, software distributed
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// under the License is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR
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// CONDITIONS OF ANY KIND, either express or implied. See the License for the
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// specific language governing permissions and limitations under the License.
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#ifndef RAPIDJSON_ALLOCATORS_H_
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#define RAPIDJSON_ALLOCATORS_H_
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#include "rapidjson.h"
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RAPIDJSON_NAMESPACE_BEGIN
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///////////////////////////////////////////////////////////////////////////////
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// Allocator
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/*! \class rapidjson::Allocator
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\brief Concept for allocating, resizing and freeing memory block.
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Note that Malloc() and Realloc() are non-static but Free() is static.
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So if an allocator need to support Free(), it needs to put its pointer in
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the header of memory block.
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\code
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concept Allocator {
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static const bool kNeedFree; //!< Whether this allocator needs to call Free().
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// Allocate a memory block.
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// \param size of the memory block in bytes.
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// \returns pointer to the memory block.
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void* Malloc(size_t size);
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// Resize a memory block.
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// \param originalPtr The pointer to current memory block. Null pointer is permitted.
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// \param originalSize The current size in bytes. (Design issue: since some allocator may not book-keep this, explicitly pass to it can save memory.)
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// \param newSize the new size in bytes.
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void* Realloc(void* originalPtr, size_t originalSize, size_t newSize);
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// Free a memory block.
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// \param pointer to the memory block. Null pointer is permitted.
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static void Free(void *ptr);
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};
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\endcode
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*/
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///////////////////////////////////////////////////////////////////////////////
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// CrtAllocator
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//! C-runtime library allocator.
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/*! This class is just wrapper for standard C library memory routines.
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\note implements Allocator concept
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*/
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class CrtAllocator {
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public:
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static const bool kNeedFree = true;
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void* Malloc(size_t size) {
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if (size) // behavior of malloc(0) is implementation defined.
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return std::malloc(size);
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else
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return NULL; // standardize to returning NULL.
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}
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void* Realloc(void* originalPtr, size_t originalSize, size_t newSize) {
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(void)originalSize;
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if (newSize == 0) {
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std::free(originalPtr);
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return NULL;
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}
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return std::realloc(originalPtr, newSize);
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}
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static void Free(void *ptr) { std::free(ptr); }
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};
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///////////////////////////////////////////////////////////////////////////////
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// MemoryPoolAllocator
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//! Default memory allocator used by the parser and DOM.
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/*! This allocator allocate memory blocks from pre-allocated memory chunks.
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It does not free memory blocks. And Realloc() only allocate new memory.
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The memory chunks are allocated by BaseAllocator, which is CrtAllocator by default.
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User may also supply a buffer as the first chunk.
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If the user-buffer is full then additional chunks are allocated by BaseAllocator.
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The user-buffer is not deallocated by this allocator.
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\tparam BaseAllocator the allocator type for allocating memory chunks. Default is CrtAllocator.
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\note implements Allocator concept
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*/
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template <typename BaseAllocator = CrtAllocator>
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class MemoryPoolAllocator {
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public:
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static const bool kNeedFree = false; //!< Tell users that no need to call Free() with this allocator. (concept Allocator)
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//! Constructor with chunkSize.
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/*! \param chunkSize The size of memory chunk. The default is kDefaultChunkSize.
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\param baseAllocator The allocator for allocating memory chunks.
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*/
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MemoryPoolAllocator(size_t chunkSize = kDefaultChunkCapacity, BaseAllocator* baseAllocator = 0) :
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chunkHead_(0), chunk_capacity_(chunkSize), userBuffer_(0), baseAllocator_(baseAllocator), ownBaseAllocator_(0)
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{
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}
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//! Constructor with user-supplied buffer.
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/*! The user buffer will be used firstly. When it is full, memory pool allocates new chunk with chunk size.
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The user buffer will not be deallocated when this allocator is destructed.
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\param buffer User supplied buffer.
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\param size Size of the buffer in bytes. It must at least larger than sizeof(ChunkHeader).
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\param chunkSize The size of memory chunk. The default is kDefaultChunkSize.
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\param baseAllocator The allocator for allocating memory chunks.
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*/
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MemoryPoolAllocator(void *buffer, size_t size, size_t chunkSize = kDefaultChunkCapacity, BaseAllocator* baseAllocator = 0) :
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chunkHead_(0), chunk_capacity_(chunkSize), userBuffer_(buffer), baseAllocator_(baseAllocator), ownBaseAllocator_(0)
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{
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RAPIDJSON_ASSERT(buffer != 0);
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RAPIDJSON_ASSERT(size > sizeof(ChunkHeader));
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chunkHead_ = reinterpret_cast<ChunkHeader*>(buffer);
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chunkHead_->capacity = size - sizeof(ChunkHeader);
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chunkHead_->size = 0;
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chunkHead_->next = 0;
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}
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//! Destructor.
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/*! This deallocates all memory chunks, excluding the user-supplied buffer.
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*/
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~MemoryPoolAllocator() {
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Clear();
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RAPIDJSON_DELETE(ownBaseAllocator_);
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}
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//! Deallocates all memory chunks, excluding the user-supplied buffer.
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void Clear() {
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while (chunkHead_ && chunkHead_ != userBuffer_) {
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ChunkHeader* next = chunkHead_->next;
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baseAllocator_->Free(chunkHead_);
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chunkHead_ = next;
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}
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if (chunkHead_ && chunkHead_ == userBuffer_)
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chunkHead_->size = 0; // Clear user buffer
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}
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//! Computes the total capacity of allocated memory chunks.
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/*! \return total capacity in bytes.
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*/
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size_t Capacity() const {
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size_t capacity = 0;
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for (ChunkHeader* c = chunkHead_; c != 0; c = c->next)
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capacity += c->capacity;
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return capacity;
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}
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//! Computes the memory blocks allocated.
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/*! \return total used bytes.
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*/
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size_t Size() const {
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size_t size = 0;
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for (ChunkHeader* c = chunkHead_; c != 0; c = c->next)
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size += c->size;
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return size;
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}
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//! Allocates a memory block. (concept Allocator)
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void* Malloc(size_t size) {
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if (!size)
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return NULL;
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size = RAPIDJSON_ALIGN(size);
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if (chunkHead_ == 0 || chunkHead_->size + size > chunkHead_->capacity)
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if (!AddChunk(chunk_capacity_ > size ? chunk_capacity_ : size))
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return NULL;
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void *buffer = reinterpret_cast<char *>(chunkHead_) + RAPIDJSON_ALIGN(sizeof(ChunkHeader)) + chunkHead_->size;
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chunkHead_->size += size;
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return buffer;
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}
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//! Resizes a memory block (concept Allocator)
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void* Realloc(void* originalPtr, size_t originalSize, size_t newSize) {
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if (originalPtr == 0)
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return Malloc(newSize);
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if (newSize == 0)
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return NULL;
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originalSize = RAPIDJSON_ALIGN(originalSize);
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newSize = RAPIDJSON_ALIGN(newSize);
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// Do not shrink if new size is smaller than original
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if (originalSize >= newSize)
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return originalPtr;
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// Simply expand it if it is the last allocation and there is sufficient space
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if (originalPtr == reinterpret_cast<char *>(chunkHead_) + RAPIDJSON_ALIGN(sizeof(ChunkHeader)) + chunkHead_->size - originalSize) {
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size_t increment = static_cast<size_t>(newSize - originalSize);
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if (chunkHead_->size + increment <= chunkHead_->capacity) {
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chunkHead_->size += increment;
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return originalPtr;
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}
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}
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// Realloc process: allocate and copy memory, do not free original buffer.
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if (void* newBuffer = Malloc(newSize)) {
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if (originalSize)
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std::memcpy(newBuffer, originalPtr, originalSize);
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return newBuffer;
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}
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else
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return NULL;
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}
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//! Frees a memory block (concept Allocator)
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static void Free(void *ptr) { (void)ptr; } // Do nothing
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private:
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//! Copy constructor is not permitted.
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MemoryPoolAllocator(const MemoryPoolAllocator& rhs) /* = delete */;
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//! Copy assignment operator is not permitted.
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MemoryPoolAllocator& operator=(const MemoryPoolAllocator& rhs) /* = delete */;
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//! Creates a new chunk.
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/*! \param capacity Capacity of the chunk in bytes.
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\return true if success.
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*/
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bool AddChunk(size_t capacity) {
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if (!baseAllocator_)
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ownBaseAllocator_ = baseAllocator_ = RAPIDJSON_NEW(BaseAllocator());
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if (ChunkHeader* chunk = reinterpret_cast<ChunkHeader*>(baseAllocator_->Malloc(RAPIDJSON_ALIGN(sizeof(ChunkHeader)) + capacity))) {
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chunk->capacity = capacity;
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chunk->size = 0;
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chunk->next = chunkHead_;
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chunkHead_ = chunk;
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return true;
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}
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else
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return false;
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}
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static const int kDefaultChunkCapacity = 64 * 1024; //!< Default chunk capacity.
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//! Chunk header for perpending to each chunk.
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/*! Chunks are stored as a singly linked list.
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*/
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struct ChunkHeader {
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size_t capacity; //!< Capacity of the chunk in bytes (excluding the header itself).
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size_t size; //!< Current size of allocated memory in bytes.
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ChunkHeader *next; //!< Next chunk in the linked list.
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};
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ChunkHeader *chunkHead_; //!< Head of the chunk linked-list. Only the head chunk serves allocation.
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size_t chunk_capacity_; //!< The minimum capacity of chunk when they are allocated.
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void *userBuffer_; //!< User supplied buffer.
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BaseAllocator* baseAllocator_; //!< base allocator for allocating memory chunks.
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BaseAllocator* ownBaseAllocator_; //!< base allocator created by this object.
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};
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RAPIDJSON_NAMESPACE_END
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#endif // RAPIDJSON_ENCODINGS_H_
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