code: private static double interpolateUsingXArrAndYStride(final double[] xArr, final double yStride,
        final int offset, final double x) {
      return cubicInterpolate(
          xArr[offset + 0], yStride * (offset + 0),
          xArr[offset + 1], yStride * (offset + 1),
          xArr[offset + 2], yStride * (offset + 2),
          xArr[offset + 3], yStride * (offset + 3),
          x);
    }
docs: In C: again-two-registers cubic_interpolate_with_x_arr_and_y_stride_aux L1402