X-Recipient: archive-cygwin AT delorie DOT com
DKIM-Filter: OpenDKIM Filter v2.11.0 sourceware.org 0CE3D3858000
DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=cygwin.com;
	s=default; t=1637744014;
	bh=AA9KUtug8AclBdmAvvEW9TCYsiPAo4PNguTsbyucFgk=;
	h=Date:To:Subject:In-Reply-To:References:List-Id:List-Unsubscribe:
	 List-Archive:List-Post:List-Help:List-Subscribe:From:Reply-To:
	 From;
	b=uZLshDUDD6oOfpkDdLq7Dje2TNgvwuDIxnL0dSv/qcqXcVxCHkKGdyARwq1FTA4H/
	 jqxAOYV2awBXG3yVZPqL8SaFmtEv8/vlGOauUfZVJdEYl/akLcFuxxM68umnVTEDku
	 d9mQLWmg/TOyCshcEtVaX2ptsZ0B+8P/mWIkAWrA=
X-Original-To: cygwin AT cygwin DOT com
Delivered-To: cygwin AT cygwin DOT com
DMARC-Filter: OpenDMARC Filter v1.4.1 sourceware.org 812573858018
DKIM-Filter: OpenDKIM Filter v2.10.3 conssluserg-01.nifty.com 1AO8q4HE009627
X-Nifty-SrcIP: [110.4.221.123]
Date: Wed, 24 Nov 2021 17:52:04 +0900
To: cygwin AT cygwin DOT com
Subject: Re: possible snprintf() regression in 3.3.2
Message-Id: <20211124175204.ff0751fd1536dde626826dd5@nifty.ne.jp>
In-Reply-To: <20211124124055.a90e254858b66d42aca6ecef@nifty.ne.jp>
References: <20211118203538 DOT a049809d57731fe375801c15 AT nifty DOT ne DOT jp>
 <YZZSzPhbqF6cQAiu AT calimero DOT vinschen DOT de>
 <fa647f83-c5ed-6dea-fcba-c8b799abe12f AT gmail DOT com>
 <YZZi3rI5msk6ksAV AT calimero DOT vinschen DOT de>
 <7545bb24-43de-cd7d-0764-55c85f1af957 AT gmx DOT com>
 <20211121001613 DOT GH10332 AT venus DOT tony DOT develop-help DOT com>
 <YZtyJDXdrMzVR2lJ AT calimero DOT vinschen DOT de>
 <YZuVRjYoG40cEGDV AT calimero DOT vinschen DOT de>
 <20211122232302 DOT GI10332 AT venus DOT tony DOT develop-help DOT com>
 <20211123173409 DOT 0db4d5ccd94501ce1b8f69ea AT nifty DOT ne DOT jp>
 <YZy45cStTTgLp0gO AT calimero DOT vinschen DOT de>
 <20211124124055 DOT a90e254858b66d42aca6ecef AT nifty DOT ne DOT jp>
X-Mailer: Sylpheed 3.7.0 (GTK+ 2.24.30; i686-pc-mingw32)
Mime-Version: 1.0
X-Spam-Status: No, score=-6.0 required=5.0 tests=BAYES_00, DKIM_SIGNED,
 DKIM_VALID, DKIM_VALID_AU, DKIM_VALID_EF, KAM_LOTSOFHASH, KAM_NUMSUBJECT,
 NICE_REPLY_A, RCVD_IN_DNSWL_NONE, RCVD_IN_MSPIKE_H2, SPF_HELO_NONE, SPF_PASS,
 TXREP autolearn=ham autolearn_force=no version=3.4.4
X-Spam-Checker-Version: SpamAssassin 3.4.4 (2020-01-24) on
 server2.sourceware.org
X-BeenThere: cygwin AT cygwin DOT com
X-Mailman-Version: 2.1.29
Precedence: list
List-Id: General Cygwin discussions and problem reports <cygwin.cygwin.com>
List-Unsubscribe: <https://cygwin.com/mailman/options/cygwin>,
 <mailto:cygwin-request AT cygwin DOT com?subject=unsubscribe>
List-Archive: <https://cygwin.com/pipermail/cygwin/>
List-Post: <mailto:cygwin AT cygwin DOT com>
List-Help: <mailto:cygwin-request AT cygwin DOT com?subject=help>
List-Subscribe: <https://cygwin.com/mailman/listinfo/cygwin>,
 <mailto:cygwin-request AT cygwin DOT com?subject=subscribe>
From: Takashi Yano via Cygwin <cygwin AT cygwin DOT com>
Reply-To: Takashi Yano <takashi DOT yano AT nifty DOT ne DOT jp>
Content-Type: text/plain; charset="us-ascii"
Content-Transfer-Encoding: 7bit
Errors-To: cygwin-bounces+archive-cygwin=delorie DOT com AT cygwin DOT com
Sender: "Cygwin" <cygwin-bounces+archive-cygwin=delorie DOT com AT cygwin DOT com>

On Wed, 24 Nov 2021 12:40:55 +0900
Takashi Yano wrote:
> On Tue, 23 Nov 2021 10:48:21 +0100
> Corinna Vinschen wrote:
> > On Nov 23 17:34, Takashi Yano via Cygwin wrote:
> > > However, in reality, for example in the case:
> > > snprintf(buf, sizeof(buf), "%.3f", 1234567890123456.789);
> > > 'ndigits' is only 3 even though total digits will be 20.
> > > 
> > > So, Tony thinks current code does not correct.
> > > 
> > > However, I think something is wrong with interpretation
> > > of 'ndigits' in dltoa.c.
> > > 
> > > printf("%.3f\n", sqrt(2)*1e70);
> > > printf("%.50f\n", sqrt(2)*1e70);
> > > 
> > > outputs
> > > 
> > > 14142135623730951759073108307330633613786387000000000000000000000000000.000
> > > 14142135623730951759073108307330633613786386978891021459448717416650727.13402790000888758223149296720949629080194006476078
> > > 
> > > Is this as intended?
> > 
> > On Linux I see
> > 
> > 14142135623730951759073108307330633613786387161811679011529922516615168.000
> > 14142135623730951759073108307330633613786387161811679011529922516615168.00000000000000000000000000000000000000000000000000
> > 
> > The newlib output for .3f probably suffers from the fact that ldtoa
> > chooses the small buffer, which restricts the number of digits to 43 or
> > 44.  But keep in mind that ldtoa *always* restricted the output to 42,
> > so you never got a more precise output anyway.  Every digit beyond digit
> > 42 is only printed due to the bigger buffer sizes.
> > 
> > So, what newlib and, in extension, Cygwin really needs at this point are
> > patches to the existing ldtoa or a change to gdtoa or equivalent.
> > 
> > https://cygwin.com/acronyms/#SHTDI
> > https://cygwin.com/acronyms/#PTC
> 
> The attached patch is the one which I think correct so far.
> 
> With this patch:
> 
> 14142135623730951759073108307330633613786386978891021459448717416650727.134
> 14142135623730951759073108307330633613786386978891021459448717416650727.13402790000888758223149296720949629080194006476078
> 
> Isn't this better than current behaviour?

The printed value is still something wrong...
sqrt(2)*1e70 should be an integer value.

sqrt(2)*1e62: OK
141421356237309519594917508377920125928940956418610020629872640.000000

sqrt(2)*1e63: NG
1414213562373095241621101250369917453154560547438491094548266395.615752

I will look into this problem.

-- 
Takashi Yano <takashi DOT yano AT nifty DOT ne DOT jp>

-- 
Problem reports:      https://cygwin.com/problems.html
FAQ:                  https://cygwin.com/faq/
Documentation:        https://cygwin.com/docs.html
Unsubscribe info:     https://cygwin.com/ml/#unsubscribe-simple