optimized sum of an array of doubles in C [duplicate]

Answer 1

I would try this for the inner loop:

    double* tmp = array;
    for (j = 0; j < ARRAY_SIZE; j++) {
        sum += *tmp;  // Use a pointer
        tmp++;        // because it is faster to increment the pointer
                      // than it is to recalculate array+j every time
        help++;
    }

or better

double* tmp = array;
double* end = array + ARRAY_SIZE; // Get rid of variable j by calculating 
                                  // the end criteria and
while (tmp != end) {              // just compare if the end is reached
    sum += *tmp;
    tmp++;
    help++;
}