Re: exp() versus the POSIX standard - Mailing list pgsql-hackers

From Tom Lane
Subject Re: exp() versus the POSIX standard
Date
Msg-id 607042.1591925141@sss.pgh.pa.us
Whole thread Raw
In response to Re: exp() versus the POSIX standard  (Darafei "Komяpa" Praliaskouski <me@komzpa.net>)
Responses Re: exp() versus the POSIX standard  (Darafei "Komяpa" Praliaskouski <me@komzpa.net>)
List pgsql-hackers
=?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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