Question

void foo(Node* p[], int size){

    _uint64 arr_of_values[_MAX_THREADS];


    for (int i=0 ; i < size ; i++ ){
         arr_of_values[i] = p[i]->....;

         // much code here 
         // 
      }
 }

vs

void foo(Node* p[], int size){

    _uint64 arr_of_values[_MAX_THREADS];

    Node* p_end = p[size];
    for ( ; p != p_end ; ){            
         arr_of_values[i] = (*p)->.....;
         p++;


         // much code here 
         // 
     }

}

I created this function to demonstrate what i am asking:

what is more efficient from the cache efficiency aspect : taking p[i] or using *p++?

(i’ll never use the p[i-x] in the rest of the code, but i may use p[i] or *p in the following calculation)

Answer 1

The problem from a cache point of view isn’t the way you are accessing the elements. In this case using a pointer or the array index is equivalent.

BTW Node* p[] is an array of pointer. So you could have possibly allocated your Node objects into distant memory areas. (For example using several ptr = new Node()). The best cache performance are gainable if:

1. Your Node are stored contiguosly into memory
2. Node size doesn’t exceed the cache size.