faster implementation of sum ( for Codility test )

Question

How can the following simple implementation of sum be faster?

private long sum( int [] a, int begin, int end ) {
    if( a == null   ) {
        ret         


        

Answer 1

Just some thought, not sure if accessing the pointer directly be faster

    int* pStart = a + begin;
    int* pEnd = a + end;
    while (pStart != pEnd)
    {
        r += *pStart++;
    }