diff_copy_entry(
    diff_T	*dprev,
    diff_T	*dp,
    int		idx_orig,
    int		idx_new)
{
    long	off;

    if (dprev == NULL)
	off = 0;
    else
	off = (dprev->df_lnum[idx_orig] + dprev->df_count[idx_orig])
	    - (dprev->df_lnum[idx_new] + dprev->df_count[idx_new]);
    dp->df_lnum[idx_new] = dp->df_lnum[idx_orig] - off;
    dp->df_count[idx_new] = dp->df_count[idx_orig];
}
diff_copy_entry(
    diff_T	*dprev,
    diff_T	*dp,
    int		idx_orig,
    int		idx_new)
{
    long	off;

    if (dprev == NULL)
	off = 0;
    else
	off = (dprev->df_lnum[idx_orig] + dprev->df_count[idx_orig])
	    - (dprev->df_lnum[idx_new] + dprev->df_count[idx_new]);
    dp->df_lnum[idx_new] = dp->df_lnum[idx_orig] - off;
    dp->df_count[idx_new] = dp->df_count[idx_orig];
}