struct Sample {
    pub v: Vec<u8>, pub c: usize,
}

fn main() {
    let mut v=Sample{v: vec![0; 16],c: 2};
    pixel(&mut v, 1)[0]=-1i16;
    pixel(&mut v, 3)[0]=1i16;
    pixel(&mut v, 3)[1]=-1i16;
    assert_eq!(v.v,vec![0,0,0,0,255,255,0,0,0,0,0,0,1,0,255,255])
}

fn pixel<'a>(buf: &'a mut Sample, pos: usize) -> &'a mut [i16] {
    let win=2*buf.c;
    let pos=pos*win;
    assert!(pos>=0 && pos+win<=buf.v.len());
    let sl: &mut [u8] = &mut buf.v[pos..pos+win];
    let slp=sl.as_mut_ptr() as *mut i16;
    unsafe {std::slice::from_raw_parts_mut(slp,buf.c)}
}