set serveroutput on
declare
	num_rows constant integer := 3;
	endianess constant number := utl_raw.machine_endian;

/*	endian_format varchar2(8);
*/
	raw_line raw(12);
	raw_piece raw(4);
	time_unix date;
	scn_wrap number;
	scn_base number;
	scn_full number;
	opts_or_thread number;
begin
/*	select endian_format into endian_format
	from v$transportable_platform t, v$database d
	where d.platform_name = t.platform_name;
*/
	for r in (select * from (select * from sys.smon_scn_time order by scn desc
				)where rownum <= num_rows) loop
		for i in reverse 1..r.num_mappings loop
			raw_line := utl_raw.substr(r.tim_scn_map, (i-1)*12+1, 12);
			time_unix := date '1970-01-01' +
				utl_raw.cast_to_binary_integer(
						utl_raw.substr(raw_line, 1, 4), endianess
								)/24/60/60;
/*			scn_base := utl_raw.cast_to_binary_integer(
						utl_raw.substr(raw_line, 5, 4), endianess);
*/
/*			raw_piece := case when endian_format='Big'
					then utl_raw.substr(raw_line, 5, 4)
					else utl_raw.reverse(utl_raw.substr(raw_line, 5, 4))
					end;
			scn_base := to_number(rawtohex(raw_piece), 'XXXXXXXX');
*/
			scn_base := utl_raw.cast_to_binary_integer(
						utl_raw.substr(raw_line, 5, 4), endianess);
			scn_base := scn_base + case when scn_base < 0
						then power(2, 32)
						else 0
						end;
			scn_wrap := utl_raw.cast_to_binary_integer(
						utl_raw.substr(raw_line, 9, 2), endianess);
			scn_full := scn_wrap * power(2, 32) + scn_base;

/*			raw_piece := case when endian_format='Big'
					then utl_raw.substr(raw_line, 11, 2)
					else utl_raw.reverse(utl_raw.substr(raw_line, 11, 2))
					end;
			opts_or_thread := to_number(rawtohex(raw_piece), 'XXXX');
*/
			opts_or_thread := utl_raw.cast_to_binary_integer(
						utl_raw.substr(raw_line, 11, 2), endianess);
			opts_or_thread := opts_or_thread + case when opts_or_thread < 0
						then power(2, 16)
						else 0
						end;

			dbms_output.put_line('. '||to_char(i, '990')||rpad(' ...', 15)||
					to_char(time_unix, 'yyyy-mm-dd hh24:mi:ss')||'  scn: '||
					to_char(scn_wrap, 'FMXXXX')||'.'||
					to_char(scn_base, 'FM0XXXXXXX')||': '||
					to_char(scn_full, 'FM9999999999999990')||' opts_or_thread:'||
					to_char(opts_or_thread, '0XXX'));
		end loop;
		time_unix := date '1970-01-01' + r.time_mp/24/60/60;
		scn_wrap := r.scn_wrp;
		scn_base := r.scn_bas;
		scn_full := r.scn;
		dbms_output.put_line(to_char(time_unix, 'yyyy-mm-dd hh24:mi:ss')||' ('||
					to_char(r.time_dp, 'yyyy-mm-dd hh24:mi:ss')||') scn: '||
					to_char(scn_wrap, 'FMXXXX')||'.'||
					to_char(scn_base, 'FM0XXXXXXX')||': '||
					to_char(scn_full, 'FM9999999999999990'));
	end loop;
end;
/

asv> select * from v$version where rownum=1;

BANNER
----------------------------------------------------------------
Oracle Database 10g Enterprise Edition Release 10.2.0.4.0 - 64bi

asv> select distinct time_dp-(time_mp/24/60/60) from sys.smon_scn_time;

TIME_DP-(TIME_MP/24
-------------------
26-05-1987 00:00:00

asv> connect system@tst
Enter password: *******
Connected.
tst> select * from v$version where rownum=1;

BANNER
--------------------------------------------------------------------------------
Oracle Database 11g Enterprise Edition Release 11.2.0.3.0 - 64bit Production

tst> select distinct time_dp-(time_mp/24/60/60) from sys.smon_scn_time;

TIME_DP-(TIME_MP/24
-------------------
01-01-1970 00:00:00