| From: | Gregory Stark <stark(at)enterprisedb(dot)com> |
|---|---|
| To: | "Tom Lane" <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
| Cc: | "Filip Krska" <filip(dot)krska(at)comstar(dot)cz>, <pgsql-bugs(at)postgresql(dot)org>, "Bruce Momjian" <bruce(at)momjian(dot)us> |
| Subject: | Re: BUG #3387: mod on non-integer returns bad result |
| Date: | 2007-06-15 16:54:46 |
| Message-ID: | 87r6odb1k9.fsf@oxford.xeocode.com |
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| Lists: | pgsql-bugs |
"Tom Lane" <tgl(at)sss(dot)pgh(dot)pa(dot)us> writes:
> Gregory Stark <stark(at)enterprisedb(dot)com> writes:
>> The source of the problem is the floating point arithmetic which is used to do
>> the individual steps in the long division.
>
> I don't think so. The ultimate source of the problem is that div_var
> can only report a finite number of digits.
In the case reported div_var was getting 70/70 = 0.99999. Which is really just
wrong. The only reason was because 1.0/70 isn't representable so (1.0/70) * 70
is slightly more than 1 which ... div_var really ought not have any trouble
representing an integer even in its finite number of digits.
--
Gregory Stark
EnterpriseDB http://www.enterprisedb.com
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