Utilities - Hash combining helper

include/ebcl/Utilities.hh

@@ -466,6 +466,11 @@ struct T_HashFunction
 template< typename T >
 uint32_t ComputeHash( T const& item );
 
+// CombineHash( &hv , T ) - Helper that consolidates multiple hashes into a
+// single value.
+template< typename T >
+void CombineHash( uint32_t& hashValue , T const& item );
+
 // Helper macros to declare and define specialised hash functions.
 #define M_DECLARE_HASH( Type ) \
 	template< > \

include/ebcl/inline/Utilities.hh

@@ -315,6 +315,12 @@ inline uint32_t ComputeHash( T const& item )
 	return T_HashFunction< T >::hash( item );
 }
 
+template< typename T >
+inline void CombineHash( uint32_t& hashValue , T const& item )
+{
+	hashValue = ComputeHash( item ) + 0x9e3779b9 + ( hashValue << 6 ) + ( hashValue >> 2 );
+}
+
 /*----------------------------------------------------------------------------*/
 // Hash function specializations for data sizes 1, 2, 4 and 8.
 
@@ -358,6 +364,18 @@ struct T_HashFunction< T , 8 >
 	}
 };
 
+/*----------------------------------------------------------------------------*/
+// Hash functions for pairs and tuples
+
+template< typename T1 , typename T2 >
+inline uint32_t ComputeHash( std::pair< T1 , T2 > const& item )
+{
+	uint32_t hv{ 0 };
+	CombineHash( hv , item.first );
+	CombineHash( hv , item.second );
+	return hv;
+}
+
 
 /*= PRIVATE IMPLEMENTATION BASE ==============================================*/