findIndexDS = (dis, clock) => {
  let left = 0;
  let right = dis.length - 1;

  while (left <= right) {
    const midindex = math.floor((left + right) / 2);
    const mid = dis[midindex];
    const midclock = mid.clock;

    if (midclock <= clock) {
      if (clock < midclock + mid.len) {
        return midindex;
      }

      left = midindex + 1;
    } else {
      right = midindex - 1;
    }
  }

  return null;
}
@param {Array<DeleteItem>} dis
@param {number} clock
@return {number|null}

@private
@function