BitField.h

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/*
  Copyright (C) 2002-2020 CERN for the benefit of the ATLAS collaboration
*/
 
#ifndef TRK_BITFIELD_H
#define TRK_BITFIELD_H
 
namespace Trk {

  template<class T>
  class BitField {
  public:
    BitField( unsigned int offset_,unsigned int bits_ );

    bool encode( unsigned int value, T& id ) const;

    unsigned int decode( T id ) const;
 
  private:
    unsigned int m_offset;    
    unsigned int m_bits;      
    unsigned int m_maxValue;  
    unsigned int m_mask;      
  };
  
  template< class T>
  bool BitField<T>::encode( unsigned int value, T& id ) const {
    // check that the value is in range
    if( value >= m_maxValue ) { return false;}
    
    // clear m_bits
    id &= ~m_mask;
    
    // set m_bits
    id |= (value<<m_offset);
    
    return true;
  }
 
  template< class T>
  unsigned int BitField<T>::decode( T id ) const {
    // apply m_mask and shift with m_offset
    return (id & m_mask) >> m_offset;
  }
 
  template< class T>
  BitField<T>::BitField( unsigned int offset_,unsigned int bits_ ) : m_offset(offset_),m_bits(bits_) {
    // calculate m_mask
    m_mask = 0;
    for( unsigned int bit = m_offset; bit < m_offset + m_bits; ++bit ) {
      m_mask |= (1<<bit);
    }
    // silly way of calculating 2^m_bits
    m_maxValue = 1;
    for( unsigned int i=0;i<m_bits;++i ) { m_maxValue *= 2;}
  }
}
 
#endif