Performance was not as expected

Revision 2
Hi everyone

I wrote a function to get the exponent of a number power of two. Here is the code:

int exp = 0;
while((n = n / 2) > 0) {
//while((n = n >> 1) > 0) {
	exp++;
}
return exp;

Then came to mind, "Well, let's replace that division operator to the shift operator, to improve performance".

The result was not the expected.

Using the division operator, the code takes about 1 second; using the shift operator, the code takes about 1.3 seconds, on same conditions.

In debug mode, I checked the disassmebly code gave me by Visual Studio (Note: I don't understand nothing about assembly language). I noticed that the assembly code was the same, except when I am using the division operator, there are two more instruction.

So, can anyone explain to me the reason of this time execution difference? I expected, in worst case, the same execution time.

Thanks in advance
Filipe Marques

UPDATE:

Here are the assembly code produced for the two methods:

while((n = n / 2) > 0) {
00CE1BD5  mov         eax,dword ptr [n]
00CE1BD8  cdq
00CE1BD9  sub         eax,edx
00CE1BDB  sar         eax,1
00CE1BDD  mov         dword ptr [n],eax
00CE1BE0  cmp         dword ptr [n],0
00CE1BE4  jle         get_exponent+41h (0CE1BF1h)

while((n = n >> 1) > 0) {
00B31BD5  mov         eax,dword ptr [n]
00B31BD8  sar         eax,1
00B31BDA  mov         dword ptr [n],eax
00B31BDD  cmp         dword ptr [n],0
00B31BE1  jle         get_exponent+3Eh (0B31BEEh)