From bug-octave-request at bevo dot che dot wisc dot edu  Mon Oct 16 23:46:55 1995
Subject: bug in Complex operator / (double, const Complex&)
From: John Eaton <jwe at bevo dot che dot wisc dot edu>
To: bug-lib-g++ at prep dot ai dot mit dot edu
cc: bug-octave at bevo dot che dot wisc dot edu
Date: Mon, 16 Oct 1995 23:46:50 -0500

Using libg++ 2.7.0 and g++ 2.7.0 on a DEC Alpha running OSF 3.2, the
following program incorrectly reports a division by zero:

$ cat foo.cc
#include <iostream.h>
#include <Complex.h>
int
main (void)
{
  Complex x (1.0, 0.0);
  Complex y (1.0e-200, 1.0e-200);
  cout << x / y << "\n";
  cout << 1.0 / y << "\n";
  return 0;
}
$ g++ -o foo foo.cc -lm
$ ./foo
(5e+199, -5e+199)
Fatal Complex arithmetic error. Attempted division by zero.

Here's a fix.  It simply uses the same trick in the definition of
operator / (double, const Complex&) as is used in the definition of
operator / (const Complex&, const Complex&).  With it, the program
above prints:

(5e+199, -5e+199)
(5e+199, -5e+199)


*** libg++-2.7.0/libg++/src/Complex.cc	Fri Jun 16 16:43:09 1995
--- Complex.cc	Mon Oct 16 23:35:47 1995
***************
*** 74,82 ****
  
  Complex /* const */ operator / (double x, const Complex& y)
  {
!   double den = norm(y);
    if (den == 0.0) y.error ("Attempted division by zero.");
!   return Complex((x * y.real()) / den, -(x * y.imag()) / den);
  }
  
  Complex /* const */ operator / (const Complex& x, double y)
--- 74,86 ----
  
  Complex /* const */ operator / (double x, const Complex& y)
  {
!   double den = fabs(y.real()) + fabs(y.imag());
    if (den == 0.0) y.error ("Attempted division by zero.");
!   double xrden = x / den;
!   double yrden = y.real() / den;
!   double yiden = y.imag() / den;
!   double nrm   = yrden * yrden + yiden * yiden;
!   return Complex(xrden * yrden / nrm, -xrden * yiden / nrm);
  }
  
  Complex /* const */ operator / (const Complex& x, double y)



Thanks,

jwe