Function compute_tuple_deltas 

fn compute_tuple_deltas(
    store: &MultiItemVariationStore<'_>,
    regions: &SparseVariationRegionList<'_>,
    var_idx: u32,
    coords: &[F2Dot14],
    tuple_len: usize,
    cache: &mut ScalarCache,
    out: &mut SmallVec<f32, 64>,
) -> Result<(), ReadError>