rdkit/Code/GraphMol/FMCS/Composition2N.h

//
//  Copyright (C) 2014 Novartis Institutes for BioMedical Research
//
//   @@ All Rights Reserved @@
//  This file is part of the RDKit.
//  The contents are covered by the terms of the BSD license
//  which is included in the file license.txt, found at the root
//  of the RDKit source tree.
//
#include <RDGeneral/export.h>
#pragma once
namespace RDKit {
namespace FMCS {
typedef unsigned long long BitSet;
class Composition2N {  // generator of 2^N-1 possible bit combinations
  BitSet Bits, InverseBits;
  BitSet MaxValue, ValueMask;  // need for inverse bitset must be 2^N-1
 public:
  Composition2N(BitSet maxValue, BitSet valueMask)
      : Bits(0), InverseBits(0), MaxValue(maxValue), ValueMask(valueMask) {}

  static void compute2N(unsigned power, BitSet& value) {
    value = 1uLL << power;
  }

  BitSet getBitSet() const {
    return InverseBits;  // inverse to generate biggest seed first and then
                         // decrease number of external bonds
  }

  bool generateNext() {
    if ((++Bits) <= MaxValue) {
      InverseBits = (~Bits + 1) & ValueMask;
      return true;
    } else {
      return false;
    }
  }
  bool is2Power() const {  // one bit is set only
    BitSet bits = getBitSet();
    unsigned n = 0;
    while (0 == (bits & 1uLL) &&
           ++n < sizeof(bits) * 8) {      // find lowest bitwise 1
      bits >>= 1u;                        // shift all zero lower bits
    }
    if (0 != (bits & 1uLL)) {
      bits >>= 1u;  // shift first set bit too
    }
    return 0 == bits;                     // remained bits except lowest 1
  }
  // unused:        bool nonZero() {return 0!=getBitSet();}
  bool isSet(unsigned bit) const { return 0 != (getBitSet() & (1uLL << bit)); }
};
}  // namespace FMCS
}  // namespace RDKit