Revision 51cf588fc030cbecb35ad67dc008e8cfef25bdc7 authored by Alec Jacobson on 06 June 2018, 23:00:33 UTC, committed by Alec Jacobson on 06 June 2018, 23:00:33 UTC
UT_SmallArray.h
/*
* Copyright (c) 2018 Side Effects Software Inc.
*
* Permission is hereby granted, free of charge, to any person obtaining a copy
* of this software and associated documentation files (the "Software"), to deal
* in the Software without restriction, including without limitation the rights
* to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
* copies of the Software, and to permit persons to whom the Software is
* furnished to do so, subject to the following conditions:
*
* The above copyright notice and this permission notice shall be included in all
* copies or substantial portions of the Software.
*
* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
* IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
* FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
* AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
* LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
* OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
* SOFTWARE.
*
* COMMENTS:
* Special case for arrays that are usually small,
* to avoid a heap allocation when the array really is small.
*/
#pragma once
#ifndef __UT_SMALLARRAY_H_INCLUDED__
#define __UT_SMALLARRAY_H_INCLUDED__
#include "UT_Array.h"
#include "SYS/SYS_Types.h"
#include <utility>
#include <stddef.h>
/// An array class with the small buffer optimization, making it ideal for
/// cases when you know it will only contain a few elements at the expense of
/// increasing the object size by MAX_BYTES (subject to alignment).
template <typename T, size_t MAX_BYTES = 64>
class UT_SmallArray : public UT_Array<T>
{
// As many elements that fit into MAX_BYTES with 1 item minimum
enum { MAX_ELEMS = MAX_BYTES/sizeof(T) < 1 ? 1 : MAX_BYTES/sizeof(T) };
public:
// gcc falsely warns about our use of offsetof() on non-POD types. We can't
// easily suppress this because it has to be done in the caller at
// instantiation time. Instead, punt to a runtime check instead.
#if defined(__clang__) || defined(_MSC_VER)
#define UT_SMALL_ARRAY_SIZE_ASSERT() \
using ThisT = UT_SmallArray<T,MAX_BYTES>; \
static_assert(offsetof(ThisT, myBuffer) == sizeof(UT_Array<T>), \
"In order for UT_Array's checks for whether it needs to free the buffer to work, " \
"the buffer must be exactly following the base class memory.")
#else
#define UT_SMALL_ARRAY_SIZE_ASSERT() \
UT_ASSERT_P(!UT_Array<T>::isHeapBuffer());
#endif
/// Default construction
UT_SmallArray()
: UT_Array<T>(/*capacity*/0)
{
UT_Array<T>::unsafeShareData((T*)myBuffer, 0, MAX_ELEMS);
UT_SMALL_ARRAY_SIZE_ASSERT();
}
/// Copy constructor
/// @{
explicit UT_SmallArray(const UT_Array<T> ©)
: UT_Array<T>(/*capacity*/0)
{
UT_Array<T>::unsafeShareData((T*)myBuffer, 0, MAX_ELEMS);
UT_SMALL_ARRAY_SIZE_ASSERT();
UT_Array<T>::operator=(copy);
}
explicit UT_SmallArray(const UT_SmallArray<T,MAX_BYTES> ©)
: UT_Array<T>(/*capacity*/0)
{
UT_Array<T>::unsafeShareData((T*)myBuffer, 0, MAX_ELEMS);
UT_SMALL_ARRAY_SIZE_ASSERT();
UT_Array<T>::operator=(copy);
}
/// @}
/// Move constructor
/// @{
UT_SmallArray(UT_Array<T> &&movable) noexcept
{
UT_Array<T>::unsafeShareData((T*)myBuffer, 0, MAX_ELEMS);
UT_SMALL_ARRAY_SIZE_ASSERT();
UT_Array<T>::operator=(std::move(movable));
}
UT_SmallArray(UT_SmallArray<T,MAX_BYTES> &&movable) noexcept
{
UT_Array<T>::unsafeShareData((T*)myBuffer, 0, MAX_ELEMS);
UT_SMALL_ARRAY_SIZE_ASSERT();
UT_Array<T>::operator=(std::move(movable));
}
/// @}
/// Initializer list constructor
explicit UT_SmallArray(std::initializer_list<T> init)
{
UT_Array<T>::unsafeShareData((T*)myBuffer, 0, MAX_ELEMS);
UT_SMALL_ARRAY_SIZE_ASSERT();
UT_Array<T>::operator=(init);
}
#undef UT_SMALL_ARRAY_SIZE_ASSERT
/// Assignment operator
/// @{
UT_SmallArray<T,MAX_BYTES> &
operator=(const UT_SmallArray<T,MAX_BYTES> ©)
{
UT_Array<T>::operator=(copy);
return *this;
}
UT_SmallArray<T,MAX_BYTES> &
operator=(const UT_Array<T> ©)
{
UT_Array<T>::operator=(copy);
return *this;
}
/// @}
/// Move operator
/// @{
UT_SmallArray<T,MAX_BYTES> &
operator=(UT_SmallArray<T,MAX_BYTES> &&movable)
{
UT_Array<T>::operator=(std::move(movable));
return *this;
}
UT_SmallArray<T,MAX_BYTES> &
operator=(UT_Array<T> &&movable)
{
UT_Array<T>::operator=(std::move(movable));
return *this;
}
/// @}
UT_SmallArray<T,MAX_BYTES> &
operator=(std::initializer_list<T> src)
{
UT_Array<T>::operator=(src);
return *this;
}
private:
alignas(T) char myBuffer[MAX_ELEMS*sizeof(T)];
};
#endif // __UT_SMALLARRAY_H_INCLUDED__
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