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/*=========================================================================
*
* Copyright NumFOCUS
*
* 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
*
* https://www.apache.org/licenses/LICENSE-2.0.txt
*
* 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 itkStructHashFunction_h
#define itkStructHashFunction_h
#include "itkIntTypes.h"
#include "itkMacro.h"
namespace itk
{
/** \class StructHashFunction
*
* \brief Generic hash function for an arbitrary struct (or class).
*
* This regards the input key as a string of bytes, and applies a
* hash function similar to one that has been used in perl. If the
* data in the input key has pointers to other classes, then the
* function will be hashing on the value of the pointer itself, not
* on the data it points to. It is imagined that this function will
* be used more for structs (with fully exposed data) than for
* general classes.
* \ingroup ITKCommon
*/
template <typename TInput>
class StructHashFunction
{
public:
/** Standard class type aliases. */
using Self = StructHashFunction;
/** Input type */
using InputType = TInput;
IdentifierType
operator()(const InputType & key) const;
};
template <typename TInput>
inline IdentifierType
StructHashFunction<TInput>::operator()(const InputType & key) const
{
auto len = static_cast<IdentifierType>(sizeof(InputType));
const auto * p = reinterpret_cast<const char *>(&key);
IdentifierType hash = 0UL;
while (len--)
{
hash = hash * 65UL + static_cast<IdentifierType>(*p++);
}
hash += (hash >> 5);
return hash;
}
} // namespace itk
#endif // ndef itkStructHashFunction_h
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