58 lines
1.6 KiB
C++
58 lines
1.6 KiB
C++
/*
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* This file is open source software, licensed to you under the terms
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* of the Apache License, Version 2.0 (the "License"). See the NOTICE file
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* distributed with this work for additional information regarding copyright
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* ownership. You may not use this file except in compliance with the License.
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*
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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,
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* software distributed under the License is distributed on an
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* "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
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* KIND, either express or implied. See the License for the
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* specific language governing permissions and limitations
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* under the License.
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*/
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/*
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* Copyright (C) 2014 Cloudius Systems, Ltd.
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*/
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#ifndef VLA_HH_
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#define VLA_HH_
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#include <memory>
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#include <new>
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#include <assert.h>
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#include <type_traits>
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// Some C APIs have a structure with a variable length array at the end.
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// This is a helper function to help allocate it.
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//
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// for a structure
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//
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// struct xx { int a; float b[0]; };
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//
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// use
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//
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// make_struct_with_vla(&xx::b, number_of_bs);
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//
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// to allocate it.
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//
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template <class S, typename E>
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inline
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std::unique_ptr<S>
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make_struct_with_vla(E S::*last, size_t nr) {
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auto fake = reinterpret_cast<S*>(0);
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size_t offset = reinterpret_cast<uintptr_t>(&(fake->*last));
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size_t element_size = sizeof((fake->*last)[0]);
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assert(offset == sizeof(S));
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auto p = ::operator new(offset + element_size * nr);
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return std::unique_ptr<S>(new (p) S());
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}
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#endif /* VLA_HH_ */
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