PVS-Studio warning V636 for TPP

double RTCalculator::getUsedForGradientRate() {
  if (rts_.size() > 0)
    return used_count_ / rts_.size();
  return 0.;
}

This suspicious code was found in TPP project by PVS-Studio static code analyzer.
Warning message is:
V636 The 'used_count_ / rts_.size()' expression was implicitly casted from 'int' type to 'double' type. Consider utilizing an explicit type cast to avoid the loss of a fractional part. An example: double A = (double)(X) / Y;. rtcalculator.cxx 6406

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