Computer Science 281

 

 

 

Hour Exam #2

 

 

 

 

 

 

Name ____________________________

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Friday, March 26

95 pts. (will be adjusted to 100 pts in the gradebook)

 

1.         (10 pts.)           Write assembly language instructions

 

            To set bit 3 of %g5

 

 

 

 

 

 

            To clear bit 3 of %g5

 

 

 

 

 

 

 

            To tst bit 3 of %g5

 

 

 

 

 

 

 

2.         (5 pts)  What is the difference between a srl instruction and a sra instruction?

 

 

 

 

 

4.         (10 pts.)           Write a small routine (call it double) which takes the address of its argument and doubles its value.  For example, if

 

                        int x = 10;

                        double(&x);

                        printf(“The value of x is now %d\n”, x);

 

            appears in an assembly language program, the value of x will be 20 upon returning to the main program.  Note that the address of x is being passed to the

            subroutine.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

5.         (10 pts.)           Write a small assembly language routine which accepts the address of a ten-element integer array in %i0 and sets each array element as follows:

 

                        for (i = 0; i < 10; ++i)

                                    a[i] = 2 * i + 1;

 

6.         (10 pts.)           The address of a 3 by 5 integer array A is in %g1.  Write the assembly language code to place the value of A[2,3] in %g2.

 

 

 

 

 

 

 

 

 

 

 

 

 

7.         (10 pts.)           %g1 contains the address of a 3 by 3 integer array A.  Write the assembly language code to zero out A[k, k] for k = 0, 1, 2 (but zero out only

            A[k][k].  The corresponding C code is something like

 

                        for (int k = 0; k < 3; ++k)

                                    A[k][k] = 0;

 

8.         (20 pts.).  %g1 contains the address of a struct with the following form:

 

            struct SimpleRec {

                        int X;

                        int Y;

                        int SUM;

                        struct SimpleRec *next;

            };

 

            a.         For the struct pointed to by %g1, add the X and Y fields and place the sum in the SUM field.  Notice that all four fields are 4 bytes each.

 

 

 

 

 

 

 

 

 

 

 

 

 

            b.         The struct pointed to by %g1 in turn points to a second struct (via next).  Place the value of the field SUM found in that second struct into %g2.

 

9.         (20 pts.)           The first thing that we do when we enter a subroutine is to execute a SAVE command , for example

 

                        save     %sp, -96, %sp

 

            What happens when we do this?  Include a discussion of the registers as seen by the calling program and the called program, and the change to the stack.  Remembering that %o6 is the %sp, and %o7 holds an instruction address, how are these registers used?