From: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
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To: | Gregory Stark <stark(at)enterprisedb(dot)com> |
Cc: | "Michael Paesold" <mpaesold(at)gmx(dot)at>, "Bruce Momjian" <bruce(at)momjian(dot)us>, pgsql-patches(at)postgresql(dot)org |
Subject: | Re: WIP: rewrite numeric division |
Date: | 2007-07-17 16:00:04 |
Message-ID: | 24585.1184688004@sss.pgh.pa.us |
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Gregory Stark <stark(at)enterprisedb(dot)com> writes:
> "Tom Lane" <tgl(at)sss(dot)pgh(dot)pa(dot)us> writes:
>> Yeah. I was basically waiting to see if anyone could come up with a
>> faster solution. Since no one seems to have an idea how to do it
>> better, I'm inclined to apply the patch for 8.3.
> My only reservation is that I don't have the numeric methods background to
> tell if it's really necessary. My fix does resolve the only actual documented
> inaccuracy in the existing method.
Well, this doesn't take a lot of numerical methods background: the
fundamental problem is that the existing code generates an *approximate*
answer, whereas people who are doing div and mod on large integers tend
to expect an *exact* answer. Approximate doesn't cut it --- there will
always be cases where an off-by-one-in-the-last-internal-place error can
carry far enough to the left to be visible to the user.
regards, tom lane
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