[Egdy] gcc has a strange behaviour -2 > 0 ?

Binary package hint: gcc

Hi,

I recompiled libtorrent library (http://libtorrent.sf.net) with
gcc (GCC) 4.1.2 20060817 (prerelease) (Ubuntu 4.1.1-11ubuntu1) and I experience a problem I didn't have with previous versions of gcc.

"allocate_resources.cpp:80: int libtorrent::saturated_add(int, int): assert « sum >= a && sum >= b » failed."

I added some debug messages to the function, as follows:

int saturated_add(int a, int b)
{
  assert(a >= 0);
  assert(b >= 0);
  assert(a <= resource_request::inf);
  assert(b <= resource_request::inf);
  assert(resource_request::inf + resource_request::inf < 0);
  int sum = a + b;
  std::cout << "a: " << a << '\n';
  std::cout << "b: " << b << '\n';
  std::cout << "(a+b) sum: " << sum << '\n';
  std::cout << "resource_request::inf: " << resource_request::inf << '\n';
  if (sum < 0){
    std::cout << "sum < 0\n";
    sum = resource_request::inf;
    std::cout << "new sum: " << sum << '\n';
  }else{
    std::cout << "sum >= 0\n";
  }
  std::cout << "sum >= a: " << (sum>=a) << '\n';
  std::cout << "sum >= b: " << (sum>=b) << '\n';
  assert(sum >= a && sum >= b);
  return sum;
}

Here is the output:

a: 2147483647
b: 2147483647
(a+b) sum: -2
resource_request::inf: 2147483647
sum >= 0
sum >= a: 0
sum >= b: 0
qbittorrent: allocate_resources.cpp:87: int libtorrent::saturated_add(int, int): assert « sum >= a && sum >= b » failed.

How can -2>=0 ??? strange, right? My machine is standard: intel centrino 32bits.
I'm compiling with this gcc:
chris@chris-laptop:~/qbittorrent_svn/src$ gcc --version
gcc (GCC) 4.1.2 20060817 (prerelease) (Ubuntu 4.1.1-11ubuntu1)

I tried again with an older gcc:
chris-laptop# gcc --version
gcc (GCC) 4.0.4 20060630 (prerelease) (Ubuntu 4.0.3-4)

and this gcc worked fine... see:
a: 2147483647
b: 2147483647
sum: -2
resource_request::inf: 2147483647
sum < 0
new sum: 2147483647
sum >= a: 1
sum >= b: 1

I don't think the problem comes from libtorrent code. With the lastest gcc the statement "-2<0" is false is this is simply wrong.