CEVA Junior Compiler Software Engineer interview questions

extern short const_arr[N] long func(short x) { static short array[N]; long res = 0; int i; for (i = N-1; i > 0;i--) array[i] = array[i - 1]; // 1 arithmetic operation + 2 operations R/W = 11 cyc * (N-1) array[0] = x; // 1 R/W = 5 cyc for (i = 0; i < N; i++) res += (long)array[i] * const_arr[i]; //2 R/W + 2 arithmetic op = 12 * N cyc return res; }
 arr = {1,2,3,4} const_arr = {8,9,10,11} func(7) arr = {1,2,3,7} res = 2. Calculate the overall running time of the above C code as a function of the array's length (n=N) . Assume that: A. Arithmetic operations (such as +,-,*,=,+=) cost one machine cycle. B. Reading/Writing from an array element costs 5 machine cycles. C. Loops have a zero overhead e.g.: for (j = 0; j < n; j++) arr[j] = a + b; The cost of the loop is 6*n machine cycles (5 writing arr[j] ,1 calculating a+b). "j = 0", "j < n", "j++" are not taken into consideration when calculating cycle count.
 *************************************** 3. Lets assume that we add the following 2 new operators to the C language: 1) inc_mod(i, n); i++; if (i >= n) i = 0; 2) dec_mod(i, n); i--; if (i < 0) i = n - 1; How can the function func() be optimized SIGNIFICANTLY in terms of run time. Assume that the function func() will be called much more than N times (thus optimizing the first multiplications of zero array elements, is not worthwhile).