Subject: lib/18170: caltontp() function in NTP subsystem ignores "seconds" field of input argument
To: None <firstname.lastname@example.org>
From: None <email@example.com>
Date: 09/04/2002 13:12:57
>Synopsis: caltontp() function in NTP subsystem ignores "seconds" field of input argument
>Arrival-Date: Wed Sep 04 13:13:00 PDT 2002
>Originator: Rob Lester
An embedded system which implements NTP support.
The function caltontp() is used to convert a date/time timestamp to
an NTP compliant "number of seconds since 1/1/1900" timestamp. From
a review of the sources, it is clear that the seconds field
"second" of the input argument "struct calendar *jt" is not used by
Note however that the function which does conversions in the other
direction - caljulian() - does create the seconds field in the output
calendar structure when necessary.
This means that if you take a calendar structure, convert it to NTP
with caltontp(), and then reverse the conversion with caljulian(),
the resulting calendar structure has a zero in the seconds field
regardless of the seconds field in the input calendar structure.
The result is that up to a 1 minute precision error can occur when
restoring a saved NTP timestamp to calendar format.
1. Instantiate a "struct calendar" variable named jt and an unsigned
long named ntp.
2. Initialize the fields in the variable jt to anything, except that
the field "second" must be non-zero.
3. Convert to an NTP timestamp: ntp = caltontp(&jt)
4. Convert back to calendar format: caljulian(ntp, &jt);
Now, jt.second is not the same as when you originally started. A loss
in precision of up to 1 minute has occurred due to the ignored
seconds field when caltontp() was called.
In caltontp(), change:
ntp_days*SECSPERDAY+SECSPERMIN*(MINSPERHR*jt->hour + jt->minute);
ntp_days*SECSPERDAY+SECSPERMIN*(MINSPERHR*jt->hour + jt->minute)