From: Tom Lane <tgl@sss.pgh.pa.us>
To: =?UTF-8?Q?Darafei_=22Kom=D1=8Fpa=22_Praliaskouski?= <me@komzpa.net>
cc: PostgreSQL Developers <pgsql-hackers@lists.postgresql.org>
Subject: Re: exp() versus the POSIX standard
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	message dated "Fri, 12 Jun 2020 03:36:26 +0300"
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Date: Thu, 11 Jun 2020 21:25:41 -0400
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=?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