0;      if (curtab->tp_diff_invalid)  ex_diffupdate(NULL);  // update after a big change      // search for a change that includes "lnum" in the list of diffblocks.     for (dp = curtab->tp_first_diff; dp != NULL; dp = dp->df_next)  if (lnum <= dp->df_lnum[idx] + dp->df_count[idx])      break;     