From: Damian McGuckin <damianm@esi.com.au>
To: Rich Felker <dalias@libc.org>
Cc: musl@lists.openwall.com, Szabolcs Nagy <nsz@port70.net>
Subject: Re: [musl] [PATCH #2] Properly simplified nextafter()
Date: Mon, 16 Aug 2021 01:10:21 +1000 (AEST) [thread overview]
Message-ID: <alpine.LRH.2.02.2108160105200.30419@key0.esi.com.au> (raw)
In-Reply-To: <20210815140310.GG13220@brightrain.aerifal.cx>
On Sun, 15 Aug 2021, Rich Felker wrote:
>> I did a quick check and ran the above code for some test cases:
>>
>> nextafter(-9.7500000000e+01, 3.5000000000e+01) = -9.7500000000e+01
>> yourpatch(-9.7500000000e+01, 3.5000000000e+01) = -9.7500000000e+01
>>
>> The error is 2.8421709430e-14
>>
>> nextafter(-9.7500000000e+01, -3.5000000000e+01) = -9.7500000000e+01
>> yourpatch(-9.7500000000e+01, -3.5000000000e+01) = -9.7500000000e+01
>>
>> The error is 2.8421709430e-14
>
> I don't follow; are you claiming Stefan's patch introduces an error
> here?
Yes. I have suggested a change which solves the problem.
> The outputs you printed show the exact same behavior before and
> after but it's possible you printed them wrong. The nextafter function
> is bit-exact;
The bits from nextafter from GLIBC match those of MUSL for that case.
But the bits from nextafter from GLIBC do not match those of Stefan's
patch for the same case.
> it does not have floating point error (inexactness)
> unless the implementation is buggy.
>> nextafter(-inf, inf) = -1.7976931349e+308 Correct
>> yourpatch(-inf, inf) = -nan Incorrect
>>
>> This is against standard GLIB.
>
> glibc I assume you mean?
Yes. Sorry. FInger<->Brain miscommunications.
> In any case yes this looks like a bug in the patch.
I believe so. Which I think Szabolcs has also suggested is the case.
Stay safe - Damian
Pacific Engineering Systems International, 277-279 Broadway, Glebe NSW 2037
Ph:+61-2-8571-0847 .. Fx:+61-2-9692-9623 | unsolicited email not wanted here
Views & opinions here are mine and not those of any past or present employer
next prev parent reply other threads:[~2021-08-15 15:10 UTC|newest]
Thread overview: 34+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-08-10 6:23 [musl] [PATCH] " Stefan Kanthak
2021-08-10 21:34 ` Szabolcs Nagy
2021-08-10 22:53 ` Stefan Kanthak
2021-08-11 2:40 ` Rich Felker
2021-08-11 15:44 ` Stefan Kanthak
2021-08-11 16:09 ` Rich Felker
2021-08-11 16:50 ` Stefan Kanthak
2021-08-11 17:57 ` Rich Felker
2021-08-11 22:16 ` Szabolcs Nagy
2021-08-11 22:43 ` Stefan Kanthak
2021-08-12 0:59 ` Rich Felker
2021-08-11 8:23 ` Szabolcs Nagy
2021-08-13 12:04 ` [musl] [PATCH #2] " Stefan Kanthak
2021-08-13 15:59 ` Rich Felker
2021-08-13 18:30 ` Stefan Kanthak
2021-08-14 4:07 ` Damian McGuckin
2021-08-14 22:45 ` Szabolcs Nagy
2021-08-14 23:46 ` Szabolcs Nagy
2021-08-15 7:04 ` Stefan Kanthak
2021-08-15 7:46 ` Ariadne Conill
2021-08-15 13:59 ` Rich Felker
2021-08-15 14:57 ` Ariadne Conill
2021-08-15 8:24 ` Damian McGuckin
2021-08-15 14:03 ` Rich Felker
2021-08-15 15:10 ` Damian McGuckin [this message]
2021-08-15 14:56 ` Szabolcs Nagy
2021-08-15 15:19 ` Stefan Kanthak
2021-08-15 15:48 ` Rich Felker
2021-08-15 16:29 ` Stefan Kanthak
2021-08-15 16:49 ` Rich Felker
2021-08-15 20:52 ` Stefan Kanthak
2021-08-15 21:48 ` Rich Felker
2021-08-15 15:52 ` Ariadne Conill
2021-08-15 16:09 ` Rich Felker
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=alpine.LRH.2.02.2108160105200.30419@key0.esi.com.au \
--to=damianm@esi.com.au \
--cc=dalias@libc.org \
--cc=musl@lists.openwall.com \
--cc=nsz@port70.net \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
Code repositories for project(s) associated with this public inbox
https://git.vuxu.org/mirror/musl/
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).