Count Leading Zero bits in an integer

How to count all zeros from left to right until reach first set (1) bit? we name it counting leading zeros :

int clz (int x)
{
 if (x ==0)
  return 32;
 int n=0;
 if ((x & 0xFFFF0000) == 0) { n += 16; x =x << 16;} //1111 1111 1111 1111 0000 0000 0000 0000 // 16 bits from left are zero! so we omit 16left bits
 if ((x & 0xFF000000) == 0){ n = n +  8; x = x <<  8;} // 8 left bits are 0
 if ((x & 0xF0000000) ==0){ n = n +  4; x = x <<  4;} // 4 left bits are 0
 if ((x & 0xC0000000) == 0){ n =n +  2, x = x <<  2;}  // 110000....0 2 left bits are zero
 if ((x & 0x80000000) == 0){n = n +  1, x = x <<  1;} // first left bit is zero
 return n;
}