[Bug c/44741] New: Complex division with NaN produces unexpected result

[Bug c/44741] New: Complex division with NaN produces unexpected result

[ian at airs dot com]

Annex G of the ISO C99 standard says that a complex value with one part being
infinity is considered an infinity, even if the other part is a NaN.  It's not
clearly stated, but presumably if neither part of the number is an infinity,
but one part is a NaN, then the number is a NaN.  And presumably if a complex
NaN is involved in a math operation, the result should be a complex NaN.

So, I would expect that dividing a complex NaN by a complex 0 would give me a
complex NaN.  However, when I run this program:


#include <stdio.h>
#include <math.h>
#include <complex.h>

__complex float
div (__complex float f1, __complex float f2)
{
  return f1 / f2;
}

int
main ()
{
  __complex float f;

  f = div (NAN + NAN * I, 0);
  printf ("%g+%g*i\n", creal (f), cimag (f));
  f = div (1.0 + NAN * I, 0);
  printf ("%g+%g*i\n", creal (f), cimag (f));
  f = div (NAN + 1.0 * I, 0);
  printf ("%g+%g*i\n", creal (f), cimag (f));
}

with current mainline, it prints

nan+nan*i
nan+nan*i
nan+inf*i

That last answer seems incorrect according to the rules of Annex G.  It is an
infinity when it should be a NaN.


-- 
           Summary: Complex division with NaN produces unexpected result
           Product: gcc
           Version: 4.6.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: ian at airs dot com


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=44741

Re: [Bug c/44741] New: Complex division with NaN produces unexpected result

[Andrew Pinski]

I think the issue is we don't implement imagainy types so 1 + nan I  
turns into nan.

On Jun 30, 2010, at 9:51 PM, "ian at airs dot com" <gcc-bugzilla@gcc.gnu.org 
 > wrote:

> Annex G of the ISO C99 standard says that a complex value with one  
> part being
> infinity is considered an infinity, even if the other part is a  
> NaN.  It's not
> clearly stated, but presumably if neither part of the number is an  
> infinity,
> but one part is a NaN, then the number is a NaN.  And presumably if  
> a complex
> NaN is involved in a math operation, the result should be a complex  
> NaN.
>
> So, I would expect that dividing a complex NaN by a complex 0 would  
> give me a
> complex NaN.  However, when I run this program:
>
>
> #include <stdio.h>
> #include <math.h>
> #include <complex.h>
>
> __complex float
> div (__complex float f1, __complex float f2)
> {
>  return f1 / f2;
> }
>
> int
> main ()
> {
>  __complex float f;
>
>  f = div (NAN + NAN * I, 0);
>  printf ("%g+%g*i\n", creal (f), cimag (f));
>  f = div (1.0 + NAN * I, 0);
>  printf ("%g+%g*i\n", creal (f), cimag (f));
>  f = div (NAN + 1.0 * I, 0);
>  printf ("%g+%g*i\n", creal (f), cimag (f));
> }
>
> with current mainline, it prints
>
> nan+nan*i
> nan+nan*i
> nan+inf*i
>
> That last answer seems incorrect according to the rules of Annex G.   
> It is an
> infinity when it should be a NaN.
>
>
> -- 
>           Summary: Complex division with NaN produces unexpected  
> result
>           Product: gcc
>           Version: 4.6.0
>            Status: UNCONFIRMED
>          Severity: normal
>          Priority: P3
>         Component: c
>        AssignedTo: unassigned at gcc dot gnu dot org
>        ReportedBy: ian at airs dot com
>
>
> http://gcc.gnu.org/bugzilla/show_bug.cgi?id=44741
>

[Bug c/44741] Complex division with NaN produces unexpected result

[pinskia at gmail dot com]

------- Comment #1 from pinskia at gmail dot com  2010-07-01 05:04 -------
Subject: Re:   New: Complex division with NaN produces unexpected result

I think the issue is we don't implement imagainy types so 1 + nan I  
turns into nan.

On Jun 30, 2010, at 9:51 PM, "ian at airs dot com" <gcc-bugzilla@gcc.gnu.org 
 > wrote:

> Annex G of the ISO C99 standard says that a complex value with one  
> part being
> infinity is considered an infinity, even if the other part is a  
> NaN.  It's not
> clearly stated, but presumably if neither part of the number is an  
> infinity,
> but one part is a NaN, then the number is a NaN.  And presumably if  
> a complex
> NaN is involved in a math operation, the result should be a complex  
> NaN.
>
> So, I would expect that dividing a complex NaN by a complex 0 would  
> give me a
> complex NaN.  However, when I run this program:
>
>
> #include <stdio.h>
> #include <math.h>
> #include <complex.h>
>
> __complex float
> div (__complex float f1, __complex float f2)
> {
>  return f1 / f2;
> }
>
> int
> main ()
> {
>  __complex float f;
>
>  f = div (NAN + NAN * I, 0);
>  printf ("%g+%g*i\n", creal (f), cimag (f));
>  f = div (1.0 + NAN * I, 0);
>  printf ("%g+%g*i\n", creal (f), cimag (f));
>  f = div (NAN + 1.0 * I, 0);
>  printf ("%g+%g*i\n", creal (f), cimag (f));
> }
>
> with current mainline, it prints
>
> nan+nan*i
> nan+nan*i
> nan+inf*i
>
> That last answer seems incorrect according to the rules of Annex G.   
> It is an
> infinity when it should be a NaN.
>
>
> -- 
>           Summary: Complex division with NaN produces unexpected  
> result
>           Product: gcc
>           Version: 4.6.0
>            Status: UNCONFIRMED
>          Severity: normal
>          Priority: P3
>         Component: c
>        AssignedTo: unassigned at gcc dot gnu dot org
>        ReportedBy: ian at airs dot com
>
>
> http://gcc.gnu.org/bugzilla/show_bug.cgi?id=44741
>


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=44741

[Bug c/44741] Complex division with NaN produces unexpected result

[paolo dot carlini at oracle dot com]

------- Comment #2 from paolo dot carlini at oracle dot com  2010-07-01 10:51 -------
Note: a very similar issue probably affects C++.


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=44741

[Bug c/44741] Complex division with NaN produces unexpected result

[pinskia at gcc dot gnu dot org]

------- Comment #3 from pinskia at gcc dot gnu dot org  2010-07-02 00:36 -------
1.0 + NAN * I is always (NaN, NaN) as we don't implement imaginary types.  So
this is the correct value since we don't do those.  

See http://www.open-std.org/jtc1/sc22/wg14/www/docs/n1464.htm for ways of the C
standard committee fixing this issue with respect of creating complex values.


-- 

pinskia at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |RESOLVED
         Resolution|                            |INVALID


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=44741