From: Tom Lane <tgl@sss.pgh.pa.us>
To: Thomas Munro <thomas.munro@gmail.com>
cc: Laurenz Albe <laurenz.albe@cybertec.at>,
        Jim Finnerty <jfinnert@amazon.com>,
        pgsql-hackers <pgsql-hackers@postgresql.org>
Subject: Re: On disable_cost
In-reply-to: 
 <CA+hUKGKuXZjCtfP7o1FcEMKFy051GmkQJG3O3tPTTi645ehR8A@mail.gmail.com>
References: 
 <CAO0i4_SSPV9TVxbbTRVLOnCyewopcc147fBZy=f2ABk15eHS+g@mail.gmail.com>
 <CA+hUKGJ0NTtLB5dv5gbuDoRirtamC--wWGNoAT4=fF2Ev1bRdA@mail.gmail.com>
 <20191101160038.wn3qkvp4psnatmm3@alap3.anarazel.de>
 <CA+Tgmob4+Eu5LN4j1XEMQDtCFFLKuUCEJebND3bWrQL0-N7VTA@mail.gmail.com>
 <1572625852934-0.post@n3.nabble.com>
 <20191101170406.w6ybnafyvpxv2ltg@development>
 <30025.1572707098@sss.pgh.pa.us> <1576018229539-0.post@n3.nabble.com>
 <6da76620383a421c2f4164bd314bab9499d2ec5c.camel@cybertec.at>
 <CA+hUKGKuXZjCtfP7o1FcEMKFy051GmkQJG3O3tPTTi645ehR8A@mail.gmail.com>
Comments: In-reply-to Thomas Munro <thomas.munro@gmail.com>
	message dated "Fri, 13 Dec 2019 15:59:32 +1300"
MIME-Version: 1.0
Content-Type: text/plain; charset="us-ascii"
Content-ID: <27167.1576439643.1@sss.pgh.pa.us>
Content-Transfer-Encoding: quoted-printable
Date: Sun, 15 Dec 2019 14:54:03 -0500
Message-ID: <27168.1576439643@sss.pgh.pa.us>
Precedence: bulk

Thomas Munro <thomas.munro@gmail.com> writes:
> On Wed, Dec 11, 2019 at 7:24 PM Laurenz Albe <laurenz.albe@cybertec.at> =
wrote:
>> Doesn't that rely on a specific implementation of double precision (IEE=
E)?
>> I thought that we don't want to limit ourselves to platforms with IEEE =
floats.

> Just by the way, you might want to read the second last paragraph of
> the commit message for 02ddd499.  The dream is over, we're never going
> to run on Vax.

Still, the proposed hack is doubling down on IEEE dependency in a way
that I quite dislike, in that (a) it doesn't just read float values
but generates new ones (and assumes that the hardware/libc will react in
a predictable way to them), (b) in a part of the code that has no damn
business having close dependencies on float format, and (c) for a gain
far smaller than what we got from the Ryu code.

We have had prior discussions about whether 02ddd499 justifies adding
more IEEE dependencies elsewhere.  I don't think it does.  IEEE 754
is not the last word that will ever be said on floating-point arithmetic,
any more than x86_64 is the last CPU architecture that anyone will ever
care about.  We should keep our dependencies on it well circumscribed.

			regards, tom lane