static double[] subFloatArrayAsDoubleArray(float[] b, int start, int end default l(b)) {
  start = max(start, 0); end = min(end, l(b));
  if (start >= end) ret new double[0];
  double[] x = new[end-start];
  for (int i = start; i < end; i++)
    x[i-start] = b[i];
  ret x;
}