code: private static final double getHllRawEstimate(final int lgConfigK, final double kxqSum) {
      final int configK = 1 << lgConfigK;
      final double correctionFactor;
      if (lgConfigK == 4) { correctionFactor = 0.673; }
      else if (lgConfigK == 5) { correctionFactor = 0.697; }
      else if (lgConfigK == 6) { correctionFactor = 0.709; }
      else { correctionFactor = 0.7213 / (1.0 + (1.079 / configK)); }
      final double hyperEst = (correctionFactor * configK * configK) / kxqSum;
      return hyperEst;
    }
docs: In C: again-two-registers.c hhb_get_raw_estimate L1167