From: Tom Lane <tgl@sss.pgh.pa.us>
To: Darafei "Komяpa" Praliaskouski <me@komzpa.net>
Cc: PostgreSQL Developers <pgsql-hackers@lists.postgresql.org>
Subject: Re: exp() versus the POSIX standard
Date: Thu, 11 Jun 2020 21:25:41 -0400
Message-ID: <607042.1591925141@sss.pgh.pa.us> (raw)
In-Reply-To: <CAC8Q8tJ09umiQdpGpGqiYRb8JOmnLztD2rQNk+o5FOx0cFBvQw@mail.gmail.com>
References: <582552.1591917752@sss.pgh.pa.us>
<583847.1591919809@sss.pgh.pa.us>
<CAC8Q8tJ09umiQdpGpGqiYRb8JOmnLztD2rQNk+o5FOx0cFBvQw@mail.gmail.com>
=?UTF-8?Q?Darafei_=22Kom=D1=8Fpa=22_Praliaskouski?= <me@komzpa.net> writes:
> I've had the same issue with multiplying two tiny numbers. Select
> 2e-300::float * 2e-300::float gives an underflow, and it is not a wanted
> thing. This looks like handmade implementation of IEEE754's underflow
> exception that should be an optional return flag in addition to well
> defined number, but became a stop-the-world exception instead.
Solving that problem is very far outside the scope of what I'm interested
in here. I think that we'd probably regret it if we try to support IEEE
subnormals, for example --- I know that all modern hardware is probably
good with those, but I'd bet against different platforms' libc functions
all behaving the same. I don't see a sane way to offer user control over
whether we throw underflow errors or not, either. (Do you really want "+"
to stop being immutable?) The darker corners of IEEE754, like inexactness
exceptions, are even less likely to be implemented consistently
everywhere.
regards, tom lane
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To: pgsql-hackers@postgresql.org
Cc: tgl@sss.pgh.pa.us, me@komzpa.net, pgsql-hackers@lists.postgresql.org
Subject: Re: exp() versus the POSIX standard
In-Reply-To: <607042.1591925141@sss.pgh.pa.us>
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