Log Message:
-----------
Fix NUMERIC modulus to properly truncate division in computation.
Division rounding was causing incorrect results. Test case:

test=> SELECT 12345678901234567890 % 123;
?column?
----------
78
(1 row)

Was returning -45.

Modified Files:
--------------
pgsql/src/backend/utils/adt:
numeric.c (r1.83 -> r1.84)
(http://developer.postgresql.org/cvsw...1=1.83&r2=1.84)

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Is this a backport?

Bruce Momjian wrote:
> Log Message:
> -----------
> Fix NUMERIC modulus to properly truncate division in computation.
> Division rounding was causing incorrect results. Test case:
>
> test=> SELECT 12345678901234567890 % 123;
> ?column?
> ----------
> 78
> (1 row)
>
> Was returning -45.
>
> Modified Files:
> --------------
> pgsql/src/backend/utils/adt:
> numeric.c (r1.83 -> r1.84)
> (http://developer.postgresql.org/cvsw...1=1.83&r2=1.84)
>
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Christopher Kings-Lynne wrote:
> Is this a backport?

No, I don't think so. It doesn't seem to be something that enough
people use to risk the change in behavior --- it might break something
that was working. But, if folks want it backported we can do it. It is
only a change to properly do modulus for numeric.

---------------------------------------------------------------------------


>
> Bruce Momjian wrote:
> > Log Message:
> > -----------
> > Fix NUMERIC modulus to properly truncate division in computation.
> > Division rounding was causing incorrect results. Test case:
> >
> > test=> SELECT 12345678901234567890 % 123;
> > ?column?
> > ----------
> > 78
> > (1 row)
> >
> > Was returning -45.
> >
> > Modified Files:
> > --------------
> > pgsql/src/backend/utils/adt:
> > numeric.c (r1.83 -> r1.84)
> > (http://developer.postgresql.org/cvsw...1=1.83&r2=1.84)
> >
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> > message can get through to the mailing list cleanly
>
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>

--
Bruce Momjian | http://candle.pha.pa.us
pgman@candle.pha.pa.us | (610) 359-1001
+ If your life is a hard drive, | 13 Roberts Road
+ Christ can be your backup. | Newtown Square, Pennsylvania 19073

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> No, I don't think so. It doesn't seem to be something that enough
> people use to risk the change in behavior --- it might break something
> that was working. But, if folks want it backported we can do it. It is
> only a change to properly do modulus for numeric.

Well, from my point of view it's an absolute mathematical error - i'd
backport it. I can't see anyone relying on it

Chris

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Christopher Kings-Lynne <chriskl@familyhealth.com.au> writes:
>> No, I don't think so. It doesn't seem to be something that enough
>> people use to risk the change in behavior --- it might break something
>> that was working. But, if folks want it backported we can do it. It is
>> only a change to properly do modulus for numeric.

> Well, from my point of view it's an absolute mathematical error - i'd
> backport it. I can't see anyone relying on it

Doesn't this patch break the basic theorem that

a = trunc(a / b) * b + (a mod b)

? If division rounds and mod doesn't, you've got pretty serious issues.

regards, tom lane

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