CS360 Midterm -- March 14, 2002. Answer/Grading for Question 1

Answer

fp:
      push #4                 / allocate ptr

      ld [fp+16] -> %r0       / Load from*4 into r1
      mov #4 -> %r1
      mul %r0, %r1 -> %r1
      ld [fp+12] -> %r0       / Load graph into r0
      add %r0, %r1 -> %r1     
      ld [r1] -> %r0          / Load graph[from] into r0
      st %r0 -> [fp]          / Store it into ptr

l1:   ld [fp] -> %r0          / while(*ptr > 0)
      ld [r0] -> %r0
      cmp %r0, %g0
      ble l2

      ld [fp] -> %r0          / if (ptr == t0) ..
      ld [r0] -> %r0
      ld [fp+20] -> %r1
      cmp %r0, %r1
      bne l3
      mov #1 -> %r0           / return 1
      ret

l3:
      ld [fp+20] -> %r0       / push to
      st %r0 -> [sp]--
      ld [fp] -> %r0          / push *ptr
      ld [r0] -> %r0
      st %r0 -> [sp]--
      ld [fp+12] -> %r0       / push graph
      st %r0 -> [sp]--
      jsr fp                  / call fp and pop the arguments
      pop #12
      cmp %r0, %g1            / compare with 1
      bne l4
      mov #1 -> %r0           / return 1
      ret

l4:
      ld [fp] -> %r0          / add 4 to ptr
      mov #4 -> %r1
      add %r0, %r1 -> %r0
      st %r0 -> [fp]

      b l1                    / go to the top of the while loop

l2:      
      mov #0 -> %r0           / return zero
      ret

Grading - 14 points

• 1 point for allocating room for ptr on the stack
• 2 points for setting ptr to graph[from]
• 1 point for (ptr > 0) and branching if false
• 1 point for (ptr == t0) and proper branching
• 1 point for returning 1
• 1 point each for the variables on the stack
• 1 point for calling fp and popping the variables
• 1 point for proper control flow on the fp test
• 1 point for incrementing ptr by 4
• 1 point for the unconditional branch to the top of the while loop.
• 1 point for returning zero.