Function decode_v4_rows 

pub fn decode_v4_rows(
    s: &BlockedStream<'_>,
    width: usize,
    height: usize,
    first_row: usize,
    out: &mut [u16],
    parallel: bool,
) -> Result<()>

Decode rows first_row..first_row + out.len() / width of a format-4 image whose width is a multiple of 14 (rows are independent).