From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (qmail 5260 invoked by alias); 10 Jul 2012 14:27:44 -0000 Received: (qmail 5245 invoked by uid 22791); 10 Jul 2012 14:27:42 -0000 X-SWARE-Spam-Status: No, hits=-4.3 required=5.0 tests=ALL_TRUSTED,AWL,BAYES_00,KHOP_THREADED X-Spam-Check-By: sourceware.org Received: from localhost (HELO gcc.gnu.org) (127.0.0.1) by sourceware.org (qpsmtpd/0.43rc1) with ESMTP; Tue, 10 Jul 2012 14:27:29 +0000 From: "vincent-gcc at vinc17 dot net" To: gcc-bugs@gcc.gnu.org Subject: [Bug gcov-profile/53915] gcov -f rounding problem Date: Tue, 10 Jul 2012 14:27:00 -0000 X-Bugzilla-Reason: CC X-Bugzilla-Type: changed X-Bugzilla-Watch-Reason: None X-Bugzilla-Product: gcc X-Bugzilla-Component: gcov-profile X-Bugzilla-Keywords: X-Bugzilla-Severity: minor X-Bugzilla-Who: vincent-gcc at vinc17 dot net X-Bugzilla-Status: UNCONFIRMED X-Bugzilla-Priority: P3 X-Bugzilla-Assigned-To: unassigned at gcc dot gnu.org X-Bugzilla-Target-Milestone: --- X-Bugzilla-Changed-Fields: Message-ID: In-Reply-To: References: X-Bugzilla-URL: http://gcc.gnu.org/bugzilla/ Auto-Submitted: auto-generated Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable MIME-Version: 1.0 Mailing-List: contact gcc-bugs-help@gcc.gnu.org; run by ezmlm Precedence: bulk List-Id: List-Archive: List-Post: List-Help: Sender: gcc-bugs-owner@gcc.gnu.org X-SW-Source: 2012-07/txt/msg00844.txt.bz2 http://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D53915 --- Comment #1 from Vincent Lef=C3=A8vre 20= 12-07-10 14:27:28 UTC --- The problem is probably in gcc/gcov.c, function format_gcov, which has: float ratio =3D bottom ? (float)top / bottom : 0; int ix; unsigned limit =3D 100; unsigned percent; for (ix =3D dp; ix--; ) limit *=3D 10; percent =3D (unsigned) (ratio * limit + (float)0.5); Using double instead of float would be a first improvement (2 occurrences in the first line, cast to be removed in the last line). Also, multiplying top= by limit (after a cast to double) before dividing by bottom should be better, = as the first operation (the multiplication) would be done exactly in practice. Something like that: percent =3D (unsigned) ((double) top * limit / bottom + 0.5); or even: percent =3D (unsigned) (((double) top * limit + (double) bottom / 2) / bo= ttom);