How come my array index is faster than pointer

Question

Why the array index is faster than pointer? Isn\'t pointer supposed to be faster than array index?

** i used time.h clock_t to tested two functions, each loop 2 mil

Answer 1

Oops, on my 64-bit system results are quite different. I've got that this

 int i;

 for(i = 0; i < size; i++)
 {
     *(a+i) = 0;
 }

is about 100 times !! slower than this

 int i;
 int * p = a;

 for(i = 0; i < size; i++)
 {
     *(p++) = 0;
 }

when compiling with -O3. This hints to me that somehow moving to next address is far easier to achieve for 64-bit cpu, than to calculate destination address from some offset. But i'm not sure.

EDIT:
This really has something related with 64-bit architecture because same code with same compile flags doesn't shows any real difference in performance on 32-bit system.