source: ThirdParty/mpqc_open/src/lib/chemistry/qc/cints/cartit.h

//
// cartit.h
//
// Copyright (C) 2001 Edward Valeev
//
// Author: Edward Valeev <edward.valeev@chemistry.gatech.edu>
// Maintainer: EV
//
// This file is part of the SC Toolkit.
//
// The SC Toolkit is free software; you can redistribute it and/or modify
// it under the terms of the GNU Library General Public License as published by
// the Free Software Foundation; either version 2, or (at your option)
// any later version.
//
// The SC Toolkit is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
// GNU Library General Public License for more details.
//
// You should have received a copy of the GNU Library General Public License
// along with the SC Toolkit; see the file COPYING.LIB.  If not, write to
// the Free Software Foundation, 675 Mass Ave, Cambridge, MA 02139, USA.
//
// The U.S. Government is granted a limited license as per AL 91-7.
//

#ifndef _chemistry_qc_cints_cartit_h
#define _chemistry_qc_cints_cartit_h

#include <chemistry/qc/basis/cartiter.h>

namespace sc {

class CartesianIterCints : public CartesianIter {
  int *avec, *bvec, *cvec;

  public:
    CartesianIterCints(int l) : CartesianIter(l) {}

    void start() {
      bfn_=b_=c_=0;
      a_=l_;
    }

    void next() {
      if (c_ < l_ - a_) {
        b_--;
        c_++;
      }
      else {
        a_--;
        c_ = 0;
        b_ = l_ - a_;
      }
      bfn_++;
    }
    
    operator int() {
      return (a_ >= 0);
    }
};

class RedundantCartesianIterCints : public RedundantCartesianIter {
  public:
    RedundantCartesianIterCints(int l) : RedundantCartesianIter(l) {}

    int bfn() {
      int i = a();
      int am = l();
      if (am == i)
        return 0;
      else {
        int j = b();
        int c = am - i;
        return ((((c+1)*c)>>1)+c-j);
      }
    }
};

class RedundantCartesianSubIterCints : public RedundantCartesianSubIter {
  public:
    RedundantCartesianSubIterCints(int l) : RedundantCartesianSubIter(l) {}

    int bfn() {
      int i = a();
      int am = l();
      if (am == i)
        return 0;
      else {
        int j = b();
        int c = am - i;
        return ((((c+1)*c)>>1)+c-j);
      }
    }
};

}

#endif

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