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Commit87de80e

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I think I've finally identified the cause of the off-by-one-second
issue in timestamp conversion that we hacked around for so long byignoring the seconds field from localtime(). It's simple: you haveto watch out for platform-specific roundoff error when reducing apossibly-fractional timestamp to integral time_t form. In particularwe 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.
1 parentd534b9e commit87de80e

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‎src/backend/utils/adt/timestamp.c

Lines changed: 17 additions & 13 deletions
Original file line numberDiff line numberDiff line change
@@ -8,7 +8,7 @@
88
*
99
*
1010
* IDENTIFICATION
11-
* $PostgreSQL: pgsql/src/backend/utils/adt/timestamp.c,v 1.106 2004/05/21 05:08:02 tgl Exp $
11+
* $PostgreSQL: pgsql/src/backend/utils/adt/timestamp.c,v 1.107 2004/05/31 18:31:51 tgl Exp $
1212
*
1313
*-------------------------------------------------------------------------
1414
*/
@@ -933,22 +933,18 @@ dt2time(Timestamp jd, int *hour, int *min, int *sec, fsec_t *fsec)
933933
*local time zone. If out of this range, leave as GMT. - tgl 97/05/27
934934
*/
935935
int
936-
timestamp2tm(Timestampdt,int*tzp,structpg_tm*tm,fsec_t*fsec,char**tzn)
936+
timestamp2tm(Timestampdt,int*tzp,structpg_tm*tm,fsec_t*fsec,char**tzn)
937937
{
938938
#ifdefHAVE_INT64_TIMESTAMP
939-
intdate,
940-
date0;
939+
intdate;
941940
int64time;
942941
#else
943-
doubledate,
944-
date0;
942+
doubledate;
945943
doubletime;
946944
#endif
947945
time_tutime;
948946
structpg_tm*tx;
949947

950-
date0=POSTGRES_EPOCH_JDATE;
951-
952948
/*
953949
* If HasCTZSet is true then we have a brute force time zone
954950
* specified. Go ahead and rotate to the local time zone since we will
@@ -983,11 +979,11 @@ timestamp2tm(Timestamp dt, int *tzp, struct pg_tm * tm, fsec_t *fsec, char **tzn
983979
#endif
984980

985981
/* Julian day routine does not work for negative Julian days */
986-
if (date<-date0)
982+
if (date<-POSTGRES_EPOCH_JDATE)
987983
return-1;
988984

989985
/* add offset to go from J2000 back to standard Julian date */
990-
date+=date0;
986+
date+=POSTGRES_EPOCH_JDATE;
991987

992988
j2date((int)date,&tm->tm_year,&tm->tm_mon,&tm->tm_mday);
993989
dt2time(time,&tm->tm_hour,&tm->tm_min,&tm->tm_sec,fsec);
@@ -1014,11 +1010,19 @@ timestamp2tm(Timestamp dt, int *tzp, struct pg_tm * tm, fsec_t *fsec, char **tzn
10141010
*/
10151011
elseif (IS_VALID_UTIME(tm->tm_year,tm->tm_mon,tm->tm_mday))
10161012
{
1013+
/*
1014+
* Convert to integer, avoiding platform-specific
1015+
* roundoff-in-wrong-direction errors, and adjust to
1016+
* Unix epoch. Note we have to do this in one step
1017+
* because the intermediate result before adjustment
1018+
* won't necessarily fit in an int32.
1019+
*/
10171020
#ifdefHAVE_INT64_TIMESTAMP
1018-
utime= ((dt /INT64CONST(1000000))
1019-
+ ((date0-UNIX_EPOCH_JDATE)*INT64CONST(86400)));
1021+
utime= (dt-*fsec)/INT64CONST(1000000)+
1022+
(POSTGRES_EPOCH_JDATE-UNIX_EPOCH_JDATE)*86400;
10201023
#else
1021-
utime= (dt+ ((date0-UNIX_EPOCH_JDATE)*86400));
1024+
utime=rint(dt-*fsec+
1025+
(POSTGRES_EPOCH_JDATE-UNIX_EPOCH_JDATE)*86400);
10221026
#endif
10231027

10241028
tx=pg_localtime(&utime);

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