gammasgn_w.cc

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/*! \file
 *  \brief Compute gamma matrix multiplication table factors
 */
 
#include "chromabase.h"
#include "util/ferm/gammasgn_w.h"
 
namespace Chroma 
{
 
  //! Anonymous namespace
  /*! \ingroup ferm */
  namespace
  {
    multi2d<int> meson_eta2;
    bool initP = false;
 
 
    //! Init gamma matrix multiplication table factors
    /*!
     * \ingroup ferm
     *
     * Initialize signs needed for  Gamma(n)*Gamma(m)=sgn(n,m)*Gamma(n ^ m)
     */
    void gammaSgnInit()
    {
      START_CODE();
 
      if (Ns != 4)
      {
        QDPIO::cerr << __func__ << ": only supports Ns=4 currently" << std::endl;
        QDP_abort(1);
      }
 
      meson_eta2.resize(Ns*Ns,Ns*Ns);
 
      for(int n = 0; n < Ns*Ns; ++n)
      {
        int nn = n;
        int n1 = nn & 1;
        nn >>= 1;
        int n2 = nn & 1;
        nn >>= 1;
        int n3 = nn & 1;
        int n4 = nn >> 1;
 
//    int ssum = (n1 + n2 + n3 + n4) & 1;
 
        for(int m = 0; m < Ns*Ns; ++m)
        {
          int mm = m;
          int m1 = mm & 1;
          mm >>= 1;
          int m2 = mm & 1;
          mm >>= 1;
          int m3 = mm & 1;
          int m4 = mm >> 1;
 
          int ssum = ((n2+n3+n4)*m1 + (n3+n4)*m2 + n4*m3) & 1;
          meson_eta2(n,m) = (ssum == 0) ? 1 : -1;
        }
      }
  
      initP = true;
 
      END_CODE();
    }
  } // end namespace
 
  //! Return gamma matrix multiplication table factors
  /*!
   * \ingroup ferm
   *
   * Initialize signs needed for  Gamma(n)*Gamma(m)=sgn(n,m)*Gamma(n ^ m)
   */
  int gammaSgn(int n, int m)
  {
    if (! initP)
      gammaSgnInit();
 
    return meson_eta2(n,m);
  }
 
}  // end namespace Chroma