算术右移给出虚假结果?

I must be absolutely crazy here, but gcc 4.7.3 on my machine is giving the most absurd result. Here is the exact code that I'm testing:

#include <iostream>

using namespace std;

int main(){
  unsigned int b = 100000;
  cout << (b>>b) << endl;
  b = b >> b;
  cout << b << endl;
  b >>= b;
  cout << b << endl;
  return 0;
}

现在，任何自行右移的数字都应该导致 0 (n/(2^n) == 0 与 整数除法、n>1 和 positive/unsigned)，但不知何故这是我的输出:

100000
100000
100000