sclass RegularPriceCells is PriceCells {
  // cell size
  settable double interval;
  
  // one of the cell limits
  settable double base;
  
  double remainder(double price) {
    ret mod(price-base, interval);
  }
  
  // TODO: not sure if this logic has rounding problems
  
  public bool isCellLimit(double price) {
    ret remainder(price) == 0;
  }
  
  public double nextCellLimit(double price) {
    double r = remainder(price);
    ret price+(1-r)*interval;
  }
  
  // next-lower cell limit or NaN if no more cells
  public double previousCellLimit(double price) {
    double r = remainder(price);
    ret price-(r == 0 ? 1 : r)*interval;
  }
}