[erlang-questions] NTP timestamp

[József Bérces]

Hi,

I would like to convert NTP timestamps (seconds elapsed since 00:00:00 January 1st, 1900) to Erlang date/time tuples (UTC). I did not find any such functions in the OTP libraries. It seems that there is no function for converting now() to UTC date and time, either.

Any help would be welcome.

Thanks,
Jozsef

[Håkan Stenholm]

something like this should work, to convert
NTP timestamps (in UTC) to {date(), time()} in UTC:

%% returns: {date(), time()}
NTPtimestamps_to_datetime(NTPSeconds) ->
%% 1900:01:01 00:00:00 in gregorian seconds
NTPBase = calendar:datetime_to_gregorian_seconds({1900,1,1}, {0,0,0}),
GregorianSec = NTPBase + NTPSeconds,
calendar:gregorian_seconds_to_datetime(Seconds).

the calendar module has the following functions for converting now() to
UTC {date(), time()}:

now_to_universal_time(Now) -> {Date, Time}
now_to_datetime(Now) -> {Date, Time}

> Thanks,
> Jozsef
>
>
>
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[Serge Aleynikov]

Here's a snippet that deals with time conversion from/to SNTP
timestamps. In the first function Sec and USec are integers in NTP format.

sntp_time_to_now(Sec, USec) ->
case Sec band 16#80000000 of
0 -> Time = Sec + 2085978496; % use base: 7-Feb-2036 @ 06:28:16 UTC
_ -> Time = Sec - 2208988800 % use base: 1-Jan-1900 @ 01:00:00 UTC
end,
{Time div 1000000, Time rem 1000000, round((USec * 1000000) / (1
bsl 32))}.

now_to_sntp_time({_,_,USec} = Now) ->
SecsSinceJan1900 = 16#80000000 bor

(calendar:datetime_to_gregorian_seconds(calendar:now_to_universal_time(Now))
- 59958230400),
{SecsSinceJan1900, round(USec * (1 bsl 32) / 1000000)}.

Serge

[Torben Hoffmann]

Try looking at http://www.trapexit.org/Todays_Date and you can use now_to_universal_time/1 as well - you have to read the manual for calendar ( http://www.erlang.org/doc/man/calendar.html) for the details.

Cheers,
Torben