Compare memory transfer speeds between the stack and the heap.

heap2stack.cpp

#include <stdlib.h>
#include <string.h>
#include <stdint.h>

long TEST_SIZE = 500000;
long SAMPLES = 60000;

void my_copy(uint64_t* a, uint64_t* b, long n){
     memcpy(b, a, n*sizeof(uint64_t));
}

int main () {
    long i;
    
    uint64_t stack[TEST_SIZE];
    uint64_t stack2[TEST_SIZE];
    uint64_t*  heap = (uint64_t*) malloc(sizeof(uint64_t)*TEST_SIZE);
    uint64_t*  heap2 = (uint64_t*) malloc(sizeof(uint64_t)*TEST_SIZE);
    
    // set some values:
    for (i=0; i< TEST_SIZE; i++)
        heap2[i]=stack2[i]=heap[i]=stack[i]=i%13;
    
    for(i=0;i<SAMPLES;i++)
        //my_copy(heap, stack, TEST_SIZE);    
        //my_copy(stack, heap, TEST_SIZE);   
        //my_copy(heap, heap2, TEST_SIZE);   
        my_copy(stack, stack2, TEST_SIZE); 

    return 0;
}

On the i7 Mac it seems that stack -> stack copies are a bit slower than heap -> heap copies which I found to be surprising.