QuasiRandom.cpp

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/***********************************************************************************\
* (c) Copyright 1998-2019 CERN for the benefit of the LHCb and ATLAS collaborations *
*                                                                                   *
* This software is distributed under the terms of the Apache version 2 licence,     *
* copied verbatim in the file "LICENSE".                                            *
*                                                                                   *
* In applying this licence, CERN does not waive the privileges and immunities       *
* granted to it by virtue of its status as an Intergovernmental Organization        *
* or submit itself to any jurisdiction.                                             *
\***********************************************************************************/
// Include files
#include <string>
 
// local
#include "GaudiUtils/QuasiRandom.h"
 
namespace Gaudi {
  namespace Utils {
    namespace QuasiRandom {
 
      uint32_t mix( uint32_t state ) {
        state += ( state << 16 );
        state ^= ( state >> 13 );
        state += ( state << 4 );
        state ^= ( state >> 7 );
        state += ( state << 10 );
        state ^= ( state >> 5 );
        state += ( state << 8 );
        state ^= ( state >> 16 );
        return state;
      }
 
      uint32_t mix32( uint32_t state, uint32_t extra ) { return mix( state + extra ); }
 
      uint32_t mix64( uint32_t state, uint64_t extra ) {
        typedef boost::low_bits_mask_t<32> mask_t;
        state = mix32( state, uint32_t( extra & mask_t::sig_bits_fast ) );
        return mix32( state, uint32_t( ( extra >> 32 ) & mask_t::sig_bits_fast ) );
      }
 
      uint32_t mixString( uint32_t state, const std::string& extra ) {
        // prefix name with ' ' until the size is a multiple of 4.
        std::string s = std::string( ( 4 - extra.size() % 4 ) % 4, ' ' ) + extra;
        for ( size_t i = 0; i < s.size() / 4; ++i ) {
          // FIXME: this might do something different on big endian vs. small endian machines...
          uint32_t x = uint32_t( s[i * 4] ) | uint32_t( s[i * 4 + 1] ) << 8 | uint32_t( s[i * 4 + 2] ) << 16 |
                       uint32_t( s[i * 4 + 3] ) << 24;
          state = mix32( state, x );
        }
        return state;
      }
    } // namespace QuasiRandom
  }   // namespace Utils
} // namespace Gaudi