From mboxrd@z Thu Jan  1 00:00:00 1970
Return-Path: <gcc-bugs-return-159145-listarch-gcc-bugs=gcc.gnu.org@gcc.gnu.org>
Received: (qmail 2536 invoked by alias); 22 Sep 2005 15:44:34 -0000
Mailing-List: contact gcc-bugs-help@gcc.gnu.org; run by ezmlm
Precedence: bulk
List-Archive: <http://gcc.gnu.org/ml/gcc-bugs/>
List-Post: <mailto:gcc-bugs@gcc.gnu.org>
List-Help: <mailto:gcc-bugs-help@gcc.gnu.org>
Sender: gcc-bugs-owner@gcc.gnu.org
Received: (qmail 2461 invoked by alias); 22 Sep 2005 15:44:06 -0000
Date: Thu, 22 Sep 2005 15:44:00 -0000
From: "gcc-bugzilla at gcc dot gnu dot org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Message-ID: <20050922154403.24014.u.strempel@gmx.de>
Reply-To: gcc-bugzilla@gcc.gnu.org
Subject: [Bug c++/24014] New: casting int to double with got wrong result
X-Bugzilla-Reason: CC
X-SW-Source: 2005-09/txt/msg02739.txt.bz2
List-Id: <gcc-bugs.sourceware.org>


	I've written an macro for log2 calculation to calculate the exponent of one value.
	Than I cast this value to from double to int.
	The 2 values double and int differs. 
	example:
	log2(8) should be 3 but after casting to int its 2.
	This bug could be reproduced on 2 different linux distributions (Debian GNU/Linux and Fedora Core 2) with different compiler versions.

Environment:
System: Linux lux 2.6.9 #2 Tue Dec 28 22:27:56 CET 2004 i686 GNU/Linux
Architecture: i686

	
host: i486-pc-linux-gnu
build: i486-pc-linux-gnu
target: i486-pc-linux-gnu
configured with: ../src/configure -v --enable-languages=c,c++,java,f77,pascal,objc,ada,treelang --prefix=/usr --mandir=/usr/share/man --infodir=/usr/share/info --with-gxx-include-dir=/usr/include/c++/3.3 --enable-shared --enable-__cxa_atexit --with-system-zlib --enable-nls --without-included-gettext --enable-clocale=gnu --enable-debug --enable-java-gc=boehm --enable-java-awt=xlib --enable-objc-gc i486-linux

How-To-Repeat:
	use this code to reproduce it
	--- code ---
	#include <math.h>
	#include <stdlib.h>
	#define log2(val) (log((val))/log(2.0))
	int main()
	{       
	      int n1=log2(8);
		double d1=log2(8);
		printf("%d %f\n",n1,d1);
		return 0;
	 }
	--- end ---
------- Additional Comments From u dot strempel at gmx dot de  2005-09-22 15:44 -------
Fix:
	For workaround I implemented a function for log2.

-- 
           Summary: casting int to double with got wrong result
           Product: gcc
           Version: 3.3.5
            Status: UNCONFIRMED
          Severity: critical
          Priority: P2
         Component: c++
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: u dot strempel at gmx dot de
                CC: gcc-bugs at gcc dot gnu dot org
 GCC build triplet: i486-pc-linux-gnu
  GCC host triplet: i486-pc-linux-gnu
GCC target triplet: i486-pc-linux-gnu


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=24014