Function ff_simple_idct84_add 

pub fn ff_simple_idct84_add(
    dest: &mut [u8],
    dest_off: usize,
    line_size: usize,
    block: &mut [i16; 64],
)

WMV2 ABT: add an 8x4 IDCT block (top or bottom half). Equivalent to upstream ff_simple_idct84_add.