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Fix imprecision from interval rounding of multiplication/division.

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Bruce, Michael Glaesemann
This commit is contained in:
Bruce Momjian
2006-09-05 01:13:40 +00:00
parent 548e2c0a01
commit 786c3c0355
2 changed files with 40 additions and 26 deletions
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55
src/backend/utils/adt/timestamp.c
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@ -8,7 +8,7 @@
*
*
* IDENTIFICATION
* $PostgreSQL: pgsql/src/backend/utils/adt/timestamp.c,v 1.166 2006/09/03 03:34:04 momjian Exp $
* $PostgreSQL: pgsql/src/backend/utils/adt/timestamp.c,v 1.167 2006/09/05 01:13:39 momjian Exp $
*
*-------------------------------------------------------------------------
*/
@ -2514,28 +2514,34 @@ interval_mul(PG_FUNCTION_ARGS)
/*
* 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.
* Floating point calculation are inherently inprecise, so these
* calculations are crafted to produce the most reliable result
* possible. TSROUND() is needed to more accurately produce whole
* numbers where appropriate.
*/
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;
month_remainder_days = (orig_month * factor - result->month) * DAYS_PER_MONTH;
month_remainder_days = TSROUND(month_remainder_days);
sec_remainder = (orig_day * factor - result->day +
month_remainder_days - (int)month_remainder_days) * SECS_PER_DAY;
sec_remainder = TSROUND(sec_remainder);
/*
* Might have 24:00:00 hours due to rounding, or >24 hours because of
* time cascade from months and days. It might still be >24 if the
* combination of cascade and the seconds factor operation itself.
*/
if (Abs(sec_remainder) >= SECS_PER_DAY)
{
result->day += (int)(sec_remainder / SECS_PER_DAY);
sec_remainder -= (int)(sec_remainder / SECS_PER_DAY) * SECS_PER_DAY;
}
/* cascade units down */
result->day += (int32) month_remainder_days;
#ifdef HAVE_INT64_TIMESTAMP
result->time = rint(span->time * factor + sec_remainder * USECS_PER_SEC);
#else
/*
* 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);
result->time = span->time * factor + sec_remainder;
#endif
PG_RETURN_INTERVAL_P(result);
@ -2574,11 +2580,16 @@ interval_div(PG_FUNCTION_ARGS)
* 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;
month_remainder_days = (orig_month / factor - result->month) * DAYS_PER_MONTH;
month_remainder_days = TSROUND(month_remainder_days);
sec_remainder = (orig_day / factor - result->day +
month_remainder_days - (int)month_remainder_days) * SECS_PER_DAY;
sec_remainder = TSROUND(sec_remainder);
if (Abs(sec_remainder) >= SECS_PER_DAY)
{
result->day += (int)(sec_remainder / SECS_PER_DAY);
sec_remainder -= (int)(sec_remainder / SECS_PER_DAY) * SECS_PER_DAY;
}
/* cascade units down */
result->day += (int32) month_remainder_days;
@ -2586,7 +2597,7 @@ interval_div(PG_FUNCTION_ARGS)
result->time = rint(span->time / factor + sec_remainder * USECS_PER_SEC);
#else
/* See TSROUND comment in interval_mul(). */
result->time = span->time / factor + TSROUND(sec_remainder);
result->time = span->time / factor + sec_remainder;
#endif
PG_RETURN_INTERVAL_P(result);