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