Generate mask indicating leftmost 1 in x.

代碼以下：

int leftmost_one(unsigned x){
 x = x | (x >> 1);
 x = x | (x >>2);
 x = x | (x >>4);
 x = x | (x >> 8);
 x = x | (x >> 16);
 printf("%x\n",x);
 return x ^(x >> 1);
}