include/GaudiKernel/EventContextHash.h

0001 /***********************************************************************************\
0002 * (c) Copyright 1998-2019 CERN for the benefit of the LHCb and ATLAS collaborations *
0003 *                                                                                   *
0004 * This software is distributed under the terms of the Apache version 2 licence,     *
0005 * copied verbatim in the file "LICENSE".                                            *
0006 *                                                                                   *
0007 * In applying this licence, CERN does not waive the privileges and immunities       *
0008 * granted to it by virtue of its status as an Intergovernmental Organization        *
0009 * or submit itself to any jurisdiction.                                             *
0010 \***********************************************************************************/
0011 #ifndef __EVENT_CONTEXT_HASH_H
0012 #define __EVENT_CONTEXT_HASH_H
0013 #include "GaudiKernel/EventContext.h"
0014 /**
0015  * @class EventContextHash Create a hash from EventContext so
0016  * EvenContexts can be used as keys in unordered maps. Hash is crated
0017  * by combining event number and event slot using the algorithm from
0018  * boost::hash_combine()
0019  *
0020  * @author Sami Kama
0021  */
0022
0023 class EventContextHash {
0024 public:
0025   size_t hash( const EventContext& ctx ) const {
0026     size_t en = ctx.evt();
0027     size_t es = ctx.slot();
0028     return en ^ ( es + ( en << 6 ) + ( en >> 2 ) );
0029   }
0030   bool equal( const EventContext& a, const EventContext& b ) const { return hash( a ) == hash( b ); }
0031
0032   std::size_t operator()( const EventContext& ctx ) const { return hash( ctx ); }
0033   bool        operator()( const EventContext& ctx, const EventContext& ctxb ) const { return equal( ctx, ctxb ); }
0034 };
0035
0036 #endif