[Bug c++/35389] New: error in norm() of STL

2008-02-27 Thread ywei at qualcomm dot com 
There is something wrong with the norm() in STL to get the norm2 of complex
numbers.

Suppose we have complex x(8,1), the norm of x should be 8*8 + 1*1 = 65,
but norm(x) returns 64, which is incorrect.

If we do complex x(8,1), there is no problem, norm(x) does return 65.

The issue is not limited to version 4.2.1. It is observed in other versions as
well.


-- 
   Summary: error in norm() of STL
   Product: gcc
   Version: 4.2.1
Status: UNCONFIRMED
  Severity: normal
  Priority: P3
 Component: c++
AssignedTo: unassigned at gcc dot gnu dot org
ReportedBy: ywei at qualcomm dot com


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=35389

[Bug c++/35389] error in norm() of STL

2008-02-27 Thread ywei at qualcomm dot com 


--- Comment #3 from ywei at qualcomm dot com  2008-02-27 20:13 ---
Subject: RE:  error in norm() of STL

I did additional test based your test code. You are right that norm()
seems to be fine. The problem happens when I try to cast the return
double value of norm() to unsigned long long (please see my test code
below and the corresponding output). Still, it bothers me that if I
carry out the norm calculation explicitly, instead of calling norm(),
there is no such an issue.

Thanks,
- Yongbin

My test code:
=
#include 
#include 

using namespace std;

main() {

   complex tt(8,1);
   double x, y;

x = norm(tt);
  double r = tt.real(), i = tt.imag();
  y = r*r + i*i;

cout << tt << "\t" << (unsigned long long)x << "\t" << (unsigned
long long)y << endl;
cout << tt << "\t" << x << "\t" << y << endl;
}
==
The output
(8,1)   64  65
(8,1)   65  65 

-Original Message-
From: rguenth at gcc dot gnu dot org [mailto:[EMAIL PROTECTED] 
Sent: Wednesday, February 27, 2008 4:44 AM
To: Wei, Yongbin
Subject: [Bug c++/35389] error in norm() of STL



--- Comment #2 from rguenth at gcc dot gnu dot org  2008-02-27 12:43
---
I used:

#include 
#include 
#include 

int main()
{
  std::complex x(8, 1);
  std::cout << std::norm(x) << std::endl;
}


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=35389

[Bug rtl-optimization/323] optimized code gives strange floating point results

2008-02-27 Thread ywei at qualcomm dot com 


--- Comment #104 from ywei at qualcomm dot com  2008-02-27 21:41 ---
Subject: RE:  optimized code gives strange floating point results

Not sure this is the same issues as 323. All three numbers, 8, 1 and 65,
should be able to represented in IEEE 754 floating-point format exactly
without any rounding or approximation. That is
 8 = 1* 2^3
  1 = 1* 2^0
  65  = (1 + 1/64) * 2^6


-Original Message-
From: pinskia at gcc dot gnu dot org [mailto:[EMAIL PROTECTED] 
Sent: Wednesday, February 27, 2008 12:39 PM
To: Wei, Yongbin
Subject: [Bug rtl-optimization/323] optimized code gives strange
floating point results



--- Comment #103 from pinskia at gcc dot gnu dot org  2008-02-27
20:38 ---
*** Bug 35389 has been marked as a duplicate of this bug. ***


-- 

pinskia at gcc dot gnu dot org changed:

   What|Removed |Added


 CC||ywei at qualcomm dot
com


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=323

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-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=323