database/postgres
database/postgres
1
0
Fork 0
mirror of https://github.com/postgres/postgres.git synced 2025-04-27 22:56:53 +03:00
Code

Fix roundoff problems in float8_timestamptz() and make_interval().

Browse Source 
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
This commit is contained in:
Tom Lane 2017-02-08 18:04:59 -05:00
parent a507b86900
commit 8f93bd8512
1 changed files with 7 additions and 5 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

12
src/backend/utils/adt/timestamp.c
View File

@ -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);