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

If you are using C or C++ and develop for modern desktop systems and are willing to learn some assembler or learn about GCC intrinsics, you could use SIMD instructions.

This library is an example of what is possible for float and double arrays, similar results should be possible for integer arithmetic since SSE has integer instructions as well.