subf32array(a, start, end)
subf64array(a, start, end)
Return a new f32/f64array with the elements of the f32/f64 array a
from index start
(inclusive) to end
(exclusive).
subf64array(#f64[1., 2., 3., 4., 5.], 2, 4)
// #[3., 4.]