From fc51c9186a095581beb40d0a46ee13ffb1f99211 Mon Sep 17 00:00:00 2001
From: Bruce Momjian <bruce@momjian.us>
Date: Sun, 3 Sep 2006 03:34:04 +0000
Subject: [PATCH] Properly round months into days and into seconds for interval
multiplication/division queries like select '41 mon 10:00:00'::interval / 10
as "pos".
Report from Michael Glaesemann
---
src/backend/utils/adt/timestamp.c | 78 ++++++++++++++------------
src/test/regress/expected/interval.out | 2 +-
2 files changed, 44 insertions(+), 36 deletions(-)
diff --git a/src/backend/utils/adt/timestamp.c b/src/backend/utils/adt/timestamp.c
index 73f341a0355..35886fd200e 100644
--- a/src/backend/utils/adt/timestamp.c
+++ b/src/backend/utils/adt/timestamp.c
@@ -8,7 +8,7 @@
*
*
* IDENTIFICATION
- * $PostgreSQL: pgsql/src/backend/utils/adt/timestamp.c,v 1.165 2006/07/13 16:49:16 momjian Exp $
+ * $PostgreSQL: pgsql/src/backend/utils/adt/timestamp.c,v 1.166 2006/09/03 03:34:04 momjian Exp $
*
*-------------------------------------------------------------------------
*/
@@ -2492,19 +2492,14 @@ interval_mul(PG_FUNCTION_ARGS)
{
Interval *span = PG_GETARG_INTERVAL_P(0);
float8 factor = PG_GETARG_FLOAT8(1);
- double month_remainder,
- day_remainder,
- month_remainder_days;
+ double month_remainder_days, sec_remainder;
+ int32 orig_month = span->month, orig_day = span->day;
Interval *result;
result = (Interval *) palloc(sizeof(Interval));
- month_remainder = span->month * factor;
- day_remainder = span->day * factor;
- result->month = (int32) month_remainder;
- result->day = (int32) day_remainder;
- month_remainder -= result->month;
- day_remainder -= result->day;
+ result->month = (int32) (span->month * factor);
+ result->day = (int32) (span->day * factor);
/*
* The above correctly handles the whole-number part of the month and day
@@ -2516,16 +2511,31 @@ interval_mul(PG_FUNCTION_ARGS)
* using justify_hours and/or justify_days.
*/
- /* fractional months full days into days */
- month_remainder_days = month_remainder * DAYS_PER_MONTH;
- result->day += (int32) month_remainder_days;
- /* fractional months partial days into time */
- day_remainder += month_remainder_days - (int32) month_remainder_days;
+ /*
+ * Fractional months full days into days.
+ *
+ * The remainders suffer from float rounding, so instead of
+ * doing the computation using just the remainder, we calculate
+ * the total number of days and subtract. Specifically, we are
+ * multipling by DAYS_PER_MONTH before dividing by factor.
+ * This greatly reduces rounding errors.
+ */
+ month_remainder_days = (orig_month * (double)DAYS_PER_MONTH) * factor -
+ result->month * (double)DAYS_PER_MONTH;
+ sec_remainder = (orig_day * (double)SECS_PER_DAY) * factor -
+ result->day * (double)SECS_PER_DAY +
+ (month_remainder_days - (int32) month_remainder_days) * SECS_PER_DAY;
+ /* cascade units down */
+ result->day += (int32) month_remainder_days;
#ifdef HAVE_INT64_TIMESTAMP
- result->time = rint(span->time * factor + day_remainder * USECS_PER_DAY);
+ result->time = rint(span->time * factor + sec_remainder * USECS_PER_SEC);
#else
- result->time = span->time * factor + day_remainder * SECS_PER_DAY;
+ /*
+ * TSROUND() needed to prevent -146:23:60.00 output on PowerPC for
+ * SELECT interval '-41 mon -12 days -360:00' * 0.3;
+ */
+ result->time = span->time * factor + TSROUND(sec_remainder);
#endif
PG_RETURN_INTERVAL_P(result);
@@ -2546,11 +2556,10 @@ interval_div(PG_FUNCTION_ARGS)
{
Interval *span = PG_GETARG_INTERVAL_P(0);
float8 factor = PG_GETARG_FLOAT8(1);
- double month_remainder,
- day_remainder,
- month_remainder_days;
+ double month_remainder_days, sec_remainder;
+ int32 orig_month = span->month, orig_day = span->day;
Interval *result;
-
+
result = (Interval *) palloc(sizeof(Interval));
if (factor == 0.0)
@@ -2558,27 +2567,26 @@ interval_div(PG_FUNCTION_ARGS)
(errcode(ERRCODE_DIVISION_BY_ZERO),
errmsg("division by zero")));
- month_remainder = span->month / factor;
- day_remainder = span->day / factor;
- result->month = (int32) month_remainder;
- result->day = (int32) day_remainder;
- month_remainder -= result->month;
- day_remainder -= result->day;
+ result->month = (int32) (span->month / factor);
+ result->day = (int32) (span->day / factor);
/*
- * Handle any fractional parts the same way as in interval_mul.
+ * Fractional months full days into days. See comment in
+ * interval_mul().
*/
+ month_remainder_days = (orig_month * (double)DAYS_PER_MONTH) / factor -
+ result->month * (double)DAYS_PER_MONTH;
+ sec_remainder = (orig_day * (double)SECS_PER_DAY) / factor -
+ result->day * (double)SECS_PER_DAY +
+ (month_remainder_days - (int32) month_remainder_days) * SECS_PER_DAY;
- /* fractional months full days into days */
- month_remainder_days = month_remainder * DAYS_PER_MONTH;
+ /* cascade units down */
result->day += (int32) month_remainder_days;
- /* fractional months partial days into time */
- day_remainder += month_remainder_days - (int32) month_remainder_days;
-
#ifdef HAVE_INT64_TIMESTAMP
- result->time = rint(span->time / factor + day_remainder * USECS_PER_DAY);
+ result->time = rint(span->time / factor + sec_remainder * USECS_PER_SEC);
#else
- result->time = span->time / factor + day_remainder * SECS_PER_DAY;
+ /* See TSROUND comment in interval_mul(). */
+ result->time = span->time / factor + TSROUND(sec_remainder);
#endif
PG_RETURN_INTERVAL_P(result);
diff --git a/src/test/regress/expected/interval.out b/src/test/regress/expected/interval.out
index 7a43e90d5db..0adda4a981d 100644
--- a/src/test/regress/expected/interval.out
+++ b/src/test/regress/expected/interval.out
@@ -218,7 +218,7 @@ SELECT '' AS ten, * FROM INTERVAL_TBL;
select avg(f1) from interval_tbl;
avg
-------------------------------------------------
- @ 4 years 1 mon 9 days 28 hours 18 mins 23 secs
+ @ 4 years 1 mon 10 days 4 hours 18 mins 23 secs
(1 row)
-- test long interval input
--
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