pub(crate) fn write_disp(&mut self, src: ISeqPos, dest: ISeqPos) {
        let num = (src - dest).to_i32() as u32;
        self[src.0 - 4] = num as u8;
        self[src.0 - 3] = (num >> 8) as u8;
        self[src.0 - 2] = (num >> 16) as u8;
        self[src.0 - 1] = (num >> 24) as u8;
    }
Write a 32-bit `disp`lacement of `dest` from `src` on `src` ISeqPos.
ruruby/src/vm/iseq.rs