1 /*=========================================================================
2  *
3  *  Copyright Insight Software Consortium
4  *
5  *  Licensed under the Apache License, Version 2.0 (the "License");
6  *  you may not use this file except in compliance with the License.
7  *  You may obtain a copy of the License at
8  *
9  *         http://www.apache.org/licenses/LICENSE-2.0.txt
10  *
11  *  Unless required by applicable law or agreed to in writing, software
12  *  distributed under the License is distributed on an "AS IS" BASIS,
13  *  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
14  *  See the License for the specific language governing permissions and
15  *  limitations under the License.
16  *
17  *=========================================================================*/
18 #ifndef itkStructHashFunction_h
19 #define itkStructHashFunction_h
20 
21 #include "itkIntTypes.h"
22 #include "itkMacro.h"
23 
24 namespace itk
25 {
26 /** \class StructHashFunction
27  *
28  *  \brief Generic hash function for an arbitrary struct (or class).
29  *
30  *  This regards the input key as a string of bytes, and applies a
31  *  hash function similar to one that has been used in perl.  If the
32  *  data in the input key has pointers to other classes, then the
33  *  function will be hashing on the value of the pointer itself, not
34  *  on the data it points to.  It is imagined that this function will
35  *  be used more for structs (with fully exposed data) than for
36  *  general classes.
37  * \ingroup ITKCommon
38  */
39 template< typename TInput >
40 class StructHashFunction
41 {
42 public:
43 
44   /** Standard class type aliases. */
45   using Self = StructHashFunction;
46 
47   /** Input type */
48   using InputType = TInput;
49 
50   IdentifierType operator()(const InputType & key) const;
51 };
52 
53 template< typename TInput >
54 inline IdentifierType
55 StructHashFunction< TInput >
operator()56 ::operator()(const InputType & key) const
57 {
58   auto len = static_cast< IdentifierType >( sizeof( InputType ) );
59   const auto * p = reinterpret_cast< const char * >( &key );
60   IdentifierType hash = 0UL;
61   while ( len-- )
62     {
63     hash = hash * 65UL + static_cast<IdentifierType>(*p++);
64     }
65   hash += ( hash >> 5 );
66   return hash;
67 }
68 }
69 
70 #endif  // ndef itkStructHashFunction_h
71