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/*
* Copyright 2021 Google Inc. All rights reserved.
*
* 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 FLATBUFFERS_ALLOCATOR_H_
#define FLATBUFFERS_ALLOCATOR_H_
#include "flatbuffers/base.h"
namespace flatbuffers {
// Allocator interface. This is flatbuffers-specific and meant only for
// `vector_downward` usage.
class Allocator {
public:
virtual ~Allocator() {}
// Allocate `size` bytes of memory.
virtual uint8_t *allocate(size_t size) = 0;
// Deallocate `size` bytes of memory at `p` allocated by this allocator.
virtual void deallocate(uint8_t *p, size_t size) = 0;
// Reallocate `new_size` bytes of memory, replacing the old region of size
// `old_size` at `p`. In contrast to a normal realloc, this grows downwards,
// and is intended specifcally for `vector_downward` use.
// `in_use_back` and `in_use_front` indicate how much of `old_size` is
// actually in use at each end, and needs to be copied.
virtual uint8_t *reallocate_downward(uint8_t *old_p, size_t old_size,
size_t new_size, size_t in_use_back,
size_t in_use_front) {
FLATBUFFERS_ASSERT(new_size > old_size); // vector_downward only grows
uint8_t *new_p = allocate(new_size);
memcpy_downward(old_p, old_size, new_p, new_size, in_use_back,
in_use_front);
deallocate(old_p, old_size);
return new_p;
}
protected:
// Called by `reallocate_downward` to copy memory from `old_p` of `old_size`
// to `new_p` of `new_size`. Only memory of size `in_use_front` and
// `in_use_back` will be copied from the front and back of the old memory
// allocation.
void memcpy_downward(uint8_t *old_p, size_t old_size, uint8_t *new_p,
size_t new_size, size_t in_use_back,
size_t in_use_front) {
memcpy(new_p + new_size - in_use_back, old_p + old_size - in_use_back,
in_use_back);
memcpy(new_p, old_p, in_use_front);
}
};
} // namespace flatbuffers
#endif // FLATBUFFERS_ALLOCATOR_H_