g++ crashes when compiling not-so-intricate source file

Binary package hint: g++-4.1

Here is the source-code that exposes the bug :

/***************************************/

#include <iostream>
using namespace std;

double arctan(double x)
{
   int i=1,n=20;
   double c=1.0,arct=0.0,paf=1.0,eps=0.00001,hab;
   hab=(x/(1+x*x));
   do
       {
           arct+=paf;
           c+=2i/(2i+1);
           paf=(c*hab);
           i++;
       }
   while((i<n)||(paf>eps));
   arct*=hab;
   return arct;
}

int main()
{
   double Pi;
   Pi=4*(4*arctan(1/5)-arctan(1/239));
   cout<<Pi<<endl;
}

/***************************************/

And here's the output :

nmaquet@nmaquet-desktop:/tmp$ g++ bug.cpp
bug.cpp: In function ‘double arctan(double)’:
bug.cpp:12: internal compiler error: in const_binop, at fold-const.c:1641
Please submit a full bug report,
with preprocessed source if appropriate.
See <URL:http://gcc.gnu.org/bugs.html> for instructions.
For Debian GNU/Linux specific bug reporting instructions,
see <URL:file:///usr/share/doc/gcc-4.1/README.Bugs>.
Preprocessed source stored into /tmp/ccgAvvVR.out file, please attach this to your bugreport.