postgres.git / summary / log / commit / refs

commit    8f93bd8512466c9b6c4dbc1e5efd0f72b8e2be9a
Author:   Tom Lane <tgl@sss.pgh.pa.us>
Date:     Wed Feb 08 23:04:59 2017 +0000

    Fix roundoff problems in float8_timestamptz() and make_interval().
    
    When converting a float value to integer microseconds, we should be careful
    to round the value to the nearest integer, typically with rint(); simply
    assigning to an int64 variable will truncate, causing apparently off-by-one
    values in cases that should work.  Most places in the datetime code got
    this right, but not these two.
    
    float8_timestamptz() is new as of commit e511d878f (9.6).  Previous
    versions effectively depended on interval_mul() to do roundoff correctly,
    which it does, so this fixes an accuracy regression in 9.6.
    
    The problem in make_interval() dates to its introduction in 9.4.  Aside
    from being careful to round not truncate, let's incorporate the hours and
    minutes inputs into the result with exact integer arithmetic, rather than
    risk introducing roundoff error where there need not have been any.
    
    float8_timestamptz() problem reported by Erik Nordström, though this is
    not his proposed patch.  make_interval() problem found by me.
    
    Discussion: https://postgr.es/m/CAHuQZDS76jTYk3LydPbKpNfw9KbACmD=49dC4BrzHcfPv6yA1A@mail.gmail.com


 src/backend/utils/adt/timestamp.c | 12 +++++++-----
 1 file changed, 7 insertions(+), 5 deletions(-)

diff --git a/src/backend/utils/adt/timestamp.c b/src/backend/utils/adt/timestamp.c
index f2784da3605..81b76314de9 100644
--- a/src/backend/utils/adt/timestamp.c
+++ b/src/backend/utils/adt/timestamp.c
@@ -788,7 +788,7 @@ float8_timestamptz(PG_FUNCTION_ARGS)
 		seconds -= ((POSTGRES_EPOCH_JDATE - UNIX_EPOCH_JDATE) * SECS_PER_DAY);
 
 #ifdef HAVE_INT64_TIMESTAMP
-		result = seconds * USECS_PER_SEC;
+		result = rint(seconds * USECS_PER_SEC);
 #else
 		result = seconds;
 #endif
@@ -1623,12 +1623,14 @@ make_interval(PG_FUNCTION_ARGS)
 	result->month = years * MONTHS_PER_YEAR + months;
 	result->day = weeks * 7 + days;
 
-	secs += hours * (double) SECS_PER_HOUR + mins * (double) SECS_PER_MINUTE;
-
 #ifdef HAVE_INT64_TIMESTAMP
-	result->time = (int64) (secs * USECS_PER_SEC);
+	result->time = hours * ((int64) SECS_PER_HOUR * USECS_PER_SEC) +
+		mins * ((int64) SECS_PER_MINUTE * USECS_PER_SEC) +
+		(int64) rint(secs * USECS_PER_SEC);
 #else
-	result->time = secs;
+	result->time = hours * (double) SECS_PER_HOUR +
+		mins * (double) SECS_PER_MINUTE +
+		secs;
 #endif
 
 	PG_RETURN_INTERVAL_P(result);


[parent: a507b86900f6]