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[2001:8b0:bf73:93f7::51bb:e332]) by smtp.gmail.com with ESMTPSA id 4fb4d7f45d1cf-658b4691d15sm2998928a12.19.2026.01.29.08.27.05 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 29 Jan 2026 08:27:05 -0800 (PST) Received: from jsm28 (helo=localhost) by digraph.polyomino.org.uk with local-esmtp (Exim 4.98.2) (envelope-from ) id 1vlUrI-0000000AZfw-2Kkk; Thu, 29 Jan 2026 16:27:04 +0000 Date: Thu, 29 Jan 2026 16:27:04 +0000 (UTC) From: Joseph Myers To: Alejandro Colomar cc: Morten Welinder , linux-man@vger.kernel.org, libc-help@sourceware.org Subject: Re: floor/ceil man pages In-Reply-To: Message-ID: References: Precedence: bulk X-Mailing-List: linux-man@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII On Thu, 29 Jan 2026, Alejandro Colomar wrote: > > "ceil(-0.5) is 0.0". I can't find a reference, but (1) this looks > > weird, and (2) it looks like libc actually returns -0.0 which makes > > more sense. As noted above, ceil(-0.0) is required to be -0.0 if if > > ceil(-0.5) were to return +0.0 it would make ceil a non-monotonic > > function. > > I have no idea. It doesn't seem to be specified by the standard. > Joseph, do you know if the floating-point group has talked anything > about this recently? round, floor, ceil, trunc and roundeven (of non-NaN) always return a result with the sign of their input, including when that result is zero. This is not anything new. -- Joseph S. Myers josmyers@redhat.com