From owner-sc22wg14+sc22wg14-domo2=www.open-std.org@open-std.org Thu Jun 9 23:32:31 2016 Return-Path: X-Original-To: sc22wg14-domo2 Delivered-To: sc22wg14-domo2@www.open-std.org Received: by www.open-std.org (Postfix, from userid 521) id C671A358759; Thu, 9 Jun 2016 23:32:31 +0200 (CEST) Delivered-To: sc22wg14@open-std.org Received: from relay1.mentorg.com (relay1.mentorg.com [192.94.38.131]) (using TLSv1 with cipher DHE-RSA-AES256-SHA (256/256 bits)) (No client certificate requested) by www.open-std.org (Postfix) with ESMTP id 39CD0356E70 for ; Thu, 9 Jun 2016 23:32:25 +0200 (CEST) Received: from nat-ies.mentorg.com ([192.94.31.2] helo=SVR-IES-FEM-01.mgc.mentorg.com) by relay1.mentorg.com with esmtp id 1bB7Yt-0002Cq-Ak from joseph_myers@mentor.com for sc22wg14@open-std.org; Thu, 09 Jun 2016 14:32:23 -0700 Received: from digraph.polyomino.org.uk (137.202.0.76) by SVR-IES-FEM-01.mgc.mentorg.com (137.202.0.104) with Microsoft SMTP Server id 14.3.224.2; Thu, 9 Jun 2016 22:32:21 +0100 Received: from jsm28 (helo=localhost) by digraph.polyomino.org.uk with local-esmtp (Exim 4.86_2) (envelope-from ) id 1bB7Yq-00061a-Mh for sc22wg14@open-std.org; Thu, 09 Jun 2016 21:32:20 +0000 Date: Thu, 9 Jun 2016 21:32:20 +0000 From: Joseph Myers X-X-Sender: jsm28@digraph.polyomino.org.uk To: Subject: FLT_EVAL_METHOD, exceptions and lvalue-to-rvalue conversion Message-ID: User-Agent: Alpine 2.20 (DEB 67 2015-01-07) MIME-Version: 1.0 Content-Type: text/plain; charset="US-ASCII" Sender: owner-sc22wg14@open-std.org Precedence: bulk Suppose that with an implementation of C11 + TS 18661-1, that defines FLT_EVAL_METHOD to 2, you have: static volatile double x = SNAN; (void) x; Suppose also that the implementation defines the "(void) x;" statement to constitute an access to volatile-qualified x. May the implementation define that access to convert x from the format of double to the format of long double, with greater range and precision, that format being used to represent double operands in accordance with the setting of FLT_EVAL_METHOD, and thereby to raise the "invalid" exception? That is, may a convertFormat operation be applied as part of lvalue-to-rvalue conversion where FLT_EVAL_METHOD implies that a wider evaluation format is in use? Even without signaling NaNs, the issue can apply to the case of exact underflow, which can be detected using pragmas from TS 18661-5, if the wider format has extra precision but not extra range and so exact underflow occurs on converting a subnormal value to the wider format. -- Joseph S. Myers joseph@codesourcery.com