Function fullpel_diamond_search 

fn fullpel_diamond_search<T: Pixel>(
    fi: &FrameInvariants<T>,
    po: PlaneOffset,
    org_region: &PlaneRegion<'_, T>,
    p_ref: &Plane<T>,
    current: &mut MotionSearchResult,
    bit_depth: usize,
    pmv: [MotionVector; 2],
    lambda: u32,
    mvx_min: isize,
    mvx_max: isize,
    mvy_min: isize,
    mvy_max: isize,
    w: usize,
    h: usize,
)

Run a full pixel diamond search. The search is run on multiple step sizes.

For each step size, candidate motion vectors are examined for improvement to the current search location. The search location is moved to the best candidate (if any). This is repeated until the search location stops moving.