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

Array dereference p[i] is *(p + i). Compilers make use of instructions that do math + dereference in 1 or 2 cycles (e.g. x86 LEA instruction) to optimize for speed.

With the pointer loop, it splits the access and offset into to separate parts and the compiler cannot optimize it.