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I think I've finally identified the cause of the off-by-one-second

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issue in timestamp conversion that we hacked around for so long by
ignoring the seconds field from localtime().  It's simple: you have
to watch out for platform-specific roundoff error when reducing a
possibly-fractional timestamp to integral time_t form.  In particular
we should subtract off the already-determined fractional fsec field.
This should be enough to get an exact answer with int64 timestamps;
with float timestamps, throw in a rint() call just to be sure.
This commit is contained in:
Tom Lane 2004-05-31 18:32:23 +00:00
parent 54427e9a1b
commit a757fd70e5
1 changed files with 17 additions and 13 deletions
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28
src/backend/utils/adt/timestamp.c
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@ -8,7 +8,7 @@
*
*
* IDENTIFICATION
* $Header: /cvsroot/pgsql/src/backend/utils/adt/timestamp.c,v 1.96 2003/09/29 00:05:25 petere Exp $
* $Header: /cvsroot/pgsql/src/backend/utils/adt/timestamp.c,v 1.96.2.1 2004/05/31 18:32:23 tgl Exp $
*
*-------------------------------------------------------------------------
*/
@ -938,13 +938,11 @@ int
timestamp2tm(Timestamp dt, int *tzp, struct tm *tm, fsec_t *fsec, char **tzn)
{
#ifdef HAVE_INT64_TIMESTAMP
int date,
date0;
int date;
int64 time;
#else
double date,
date0;
double date;
double time;
#endif
time_t utime;
@ -953,8 +951,6 @@ timestamp2tm(Timestamp dt, int *tzp, struct tm * tm, fsec_t *fsec, char **tzn)
struct tm *tx;
#endif
date0 = POSTGRES_EPOCH_JDATE;
/*
* If HasCTZSet is true then we have a brute force time zone
* specified. Go ahead and rotate to the local time zone since we will
@ -989,11 +985,11 @@ timestamp2tm(Timestamp dt, int *tzp, struct tm * tm, fsec_t *fsec, char **tzn)
#endif
/* Julian day routine does not work for negative Julian days */
if (date < -date0)
if (date < -POSTGRES_EPOCH_JDATE)
return -1;
/* add offset to go from J2000 back to standard Julian date */
date += date0;
date += POSTGRES_EPOCH_JDATE;
j2date((int) date, &tm->tm_year, &tm->tm_mon, &tm->tm_mday);
dt2time(time, &tm->tm_hour, &tm->tm_min, &tm->tm_sec, fsec);
@ -1022,11 +1018,19 @@ timestamp2tm(Timestamp dt, int *tzp, struct tm * tm, fsec_t *fsec, char **tzn)
*/
else if (IS_VALID_UTIME(tm->tm_year, tm->tm_mon, tm->tm_mday))
{
/*
* Convert to integer, avoiding platform-specific
* roundoff-in-wrong-direction errors, and adjust to
* Unix epoch. Note we have to do this in one step
* because the intermediate result before adjustment
* won't necessarily fit in an int32.
*/
#ifdef HAVE_INT64_TIMESTAMP
utime = ((dt / INT64CONST(1000000))
+ ((date0 - UNIX_EPOCH_JDATE) * INT64CONST(86400)));
utime = (dt - *fsec) / INT64CONST(1000000) +
(POSTGRES_EPOCH_JDATE - UNIX_EPOCH_JDATE) * 86400;
#else
utime = (dt + ((date0 - UNIX_EPOCH_JDATE) * 86400));
utime = rint(dt - *fsec +
(POSTGRES_EPOCH_JDATE - UNIX_EPOCH_JDATE) * 86400);
#endif
#if defined(HAVE_TM_ZONE) || defined(HAVE_INT_TIMEZONE)