Re: Bug in numeric multiplication

From: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
To: Dean Rasheed <dean(dot)a(dot)rasheed(at)gmail(dot)com>
Cc: PostgreSQL Hackers <pgsql-hackers(at)postgresql(dot)org>
Subject: Re: Bug in numeric multiplication
Date: 2015-09-21 15:09:14
Message-ID: 28880.1442848154@sss.pgh.pa.us
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I wrote:
> Dean Rasheed <dean(dot)a(dot)rasheed(at)gmail(dot)com> writes:
>> The problem then arises in the final carry propagation pass. During
>> this phase of the computation, the carry from one digit (which can be
>> a shade under INT_MAX / NBASE) is added to the next digit, and that's
>> where the overflow happens.

> Nice catch! I think the comment could use a little more work, but I'll
> adjust it and push.

After trying to rework the comment to explain what maxdig really meant
after your changes, I came to the conclusion that it'd be better to do
it as per attached. Does this look sane to you?

regards, tom lane

Attachment Content-Type Size
numeric-mul-2.patch text/x-diff 6.2 KB

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