Re: c++/5060: Comparisons between double on gcc 2.96

Re: c++/5060: Comparisons between double on gcc 2.96

[rodrigc]

The following reply was made to PR c++/5060; it has been noted by GNATS.

From: rodrigc@gcc.gnu.org
To: chailan@sand.cad.cea.fr, gcc-bugs@gcc.gnu.org, gcc-gnats@gcc.gnu.org,
  gcc-prs@gcc.gnu.org, nobody@gcc.gnu.org
Cc:  
Subject: Re: c++/5060: Comparisons between double on gcc 2.96
Date: 12 Dec 2001 00:36:57 -0000

 Synopsis: Comparisons between double on gcc 2.96
 
 State-Changed-From-To: analyzed->closed
 State-Changed-By: rodrigc
 State-Changed-When: Tue Dec 11 16:36:56 2001
 State-Changed-Why:
     Refer to "excess precision"
 
 http://gcc.gnu.org/cgi-bin/gnatsweb.pl?cmd=view%20audit-trail&pr=5060&database=gcc

Re: c++/5060: Comparisons between double on gcc 2.96

[rodrigc]

Synopsis: Comparisons between double on gcc 2.96

State-Changed-From-To: analyzed->closed
State-Changed-By: rodrigc
State-Changed-When: Tue Dec 11 16:36:56 2001
State-Changed-Why:
    Refer to "excess precision"

http://gcc.gnu.org/cgi-bin/gnatsweb.pl?cmd=view%20audit-trail&pr=5060&database=gcc

Re: c++/5060: Comparisons between double on gcc 2.96

[Richard Henderson]

The following reply was made to PR c++/5060; it has been noted by GNATS.

From: Richard Henderson <rth@redhat.com>
To: rodrigc@gcc.gnu.org
Cc: chailan@sand.cad.cea.fr, gcc-bugs@gcc.gnu.org, gcc-gnats@gcc.gnu.org,
       gcc-prs@gcc.gnu.org, nobody@gcc.gnu.org
Subject: Re: c++/5060: Comparisons between double on gcc 2.96
Date: Mon, 10 Dec 2001 16:55:44 -0800

 On Mon, Dec 10, 2001 at 07:43:54PM -0000, rodrigc@gcc.gnu.org wrote:
 >           double z = 1.0/i ;
 >           double o_x = x ;
 >           x = x + z ;
 >           printf("i:%g %20.20g %20.20g   ", i, z+ o_x, x);
 >           double q = o_x+z;
 >           //if( ! (x==(double)(o_x+z))) std::cout <<"HELP!";
 
 Seach for "excess precision" on this list.  This is faq.
 
 
 r~

Re: c++/5060: Comparisons between double on gcc 2.96

[rodrigc]

The following reply was made to PR c++/5060; it has been noted by GNATS.

From: rodrigc@gcc.gnu.org
To: chailan@sand.cad.cea.fr, gcc-bugs@gcc.gnu.org, gcc-gnats@gcc.gnu.org,
  gcc-prs@gcc.gnu.org, nobody@gcc.gnu.org
Cc:  
Subject: Re: c++/5060: Comparisons between double on gcc 2.96
Date: 10 Dec 2001 19:43:54 -0000

 Synopsis: Comparisons between double on gcc 2.96
 
 State-Changed-From-To: open->analyzed
 State-Changed-By: rodrigc
 State-Changed-When: Mon Dec 10 11:43:54 2001
 State-Changed-Why:
     Reproduced with gcc 3.0 and gcc 3.1 on Linux on x86.
     
     The problem goes away if I change your testcase to:
     
     #include <cstddef>
     #include <iostream>
     #include <cstdio>
     using namespace std;
      
     int main()
     {
        double x = 0.0 ;
        std::cout << "Testing floating point behaviour" << std::endl ;
        for( double i=1 ; i<10 ; i++ )
        {
           double z = 1.0/i ;
           double o_x = x ;
           x = x + z ;
           printf("i:%g %20.20g %20.20g   ", i, z+ o_x, x);
           double q = o_x+z;
           //if( ! (x==(double)(o_x+z))) std::cout <<"HELP!";
           if( ! (x==q)) std::cout <<"HELP!";
           std::cout << std::endl;
      
        }
      
     }
 
 http://gcc.gnu.org/cgi-bin/gnatsweb.pl?cmd=view%20audit-trail&pr=5060&database=gcc

Re: c++/5060: Comparisons between double on gcc 2.96

[rodrigc]

Synopsis: Comparisons between double on gcc 2.96

State-Changed-From-To: open->analyzed
State-Changed-By: rodrigc
State-Changed-When: Mon Dec 10 11:43:54 2001
State-Changed-Why:
    Reproduced with gcc 3.0 and gcc 3.1 on Linux on x86.
    
    The problem goes away if I change your testcase to:
    
    #include <cstddef>
    #include <iostream>
    #include <cstdio>
    using namespace std;
     
    int main()
    {
       double x = 0.0 ;
       std::cout << "Testing floating point behaviour" << std::endl ;
       for( double i=1 ; i<10 ; i++ )
       {
          double z = 1.0/i ;
          double o_x = x ;
          x = x + z ;
          printf("i:%g %20.20g %20.20g   ", i, z+ o_x, x);
          double q = o_x+z;
          //if( ! (x==(double)(o_x+z))) std::cout <<"HELP!";
          if( ! (x==q)) std::cout <<"HELP!";
          std::cout << std::endl;
     
       }
     
    }

http://gcc.gnu.org/cgi-bin/gnatsweb.pl?cmd=view%20audit-trail&pr=5060&database=gcc

c++/5060: Comparisons between double on gcc 2.96

[chailan]

>Number:         5060
>Category:       c++
>Synopsis:       Comparisons between double on gcc 2.96
>Confidential:   no
>Severity:       serious
>Priority:       medium
>Responsible:    unassigned
>State:          open
>Class:          sw-bug
>Submitter-Id:   net
>Arrival-Date:   Mon Dec 10 04:26:02 PST 2001
>Closed-Date:
>Last-Modified:
>Originator:     chailan
>Release:        2.96
>Organization:
>Environment:
Linux  2.4.3-20mdk #1 Sun Apr 15 23:03:10 CEST 2001 i686 unknown
>Description:
Suspicious comparisons between double in following sample.
>How-To-Repeat:
Compile and run to see HELP warnings.
>Fix:

>Release-Note:
>Audit-Trail:
>Unformatted:
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