static double[] linearlyShortenArray(double[] a, int newLength) {
  int l = l(a);
  if (newLength == l) ret a;
  double[] b = new[newLength];
  double x = 0, step = doubleRatio(newLength, l);
  for i to newLength: {
    b[i] = a[iround(x)];
    x += step;
  }
  ret b;
}

static short[] linearlyShortenArray(short[] a, int newLength) {
  int l = l(a);
  if (newLength == l) ret a;
  short[] b = new[newLength];
  double x = 0, step = doubleRatio(newLength, l);
  for i to newLength: {
    b[i] = a[iround(x)];
    x += step;
  }
  ret b;
}