Solutions to Exam #2, CS 347, Spring '98

1. 
  A.  0x18, 0x30
  B.
    a: largest
    b: &array[i]
    c: i
    d: array
    e: array[i]
    f: length
    g: 0
2. 
  A. 32
  B. 16
  C. To save during call to fib(n-2)
  D. 8
  E. It's a callee save register used by fib
  F. r26, the return pointer
  G. Nothing.  It's there to pad for alignment

3. 
  A.
    s4subq $1, $1, $2 # (4-1) * x
  B. 
    s8addq $1, $1, $2 # 8x +x = 9x
    addq   $2, $2, $2 # 9x + 9 x = 18x 
  C. 
    subq $31, $1, $2  # 0 - x = -x
    s8subq $2, $2, $2 # 8*-x -(-x) = -7x
  D. 
    s8subq $1, $1, $2 # 8x - x = 7x
    s8subq $2, $1, $2 # 8*(7x) - x = 55x
4. 
  A. 111001 00111 00000000000000000101
  B. $7
  C. 0x100 + 4 + 4*5 = 0x118
5. 
  A. 010000 11111 00000101 1 0000000 010100
  B. $31, 5
  C. $4
  D. 0x00

6. 
  16 bytes:
  11 11 22 -- 33 -- -- -- 44 44 44 44 44 44 44 44
  (where -- indicates a byte that is not set by the code) 
7.
  16 bytes (only 9 needed, but 7 added)
  11 22 33 44 44 44 44 44 -- -- -- -- -- -- -- --
8.
  mulq $17, 760, $2 # $2 = 760 * x
  addq $2, $18, $2  # $2 = 760 * x + y
  s4subq $2, $2, $2 # $2 = 3*(760x + y)
  addq $2, $16, $2  # $2 = &s[x][y].red
9. 
  A. 188:
     1*1 (initialization) + 21*7 (test) + 20*1 (update) + 20*1 (body)
  B. x = 21, y = 40 (loop test succeeds 20 times and fails 1 time)   

10. 
  A. 88:
     1*6 (initialization) + 21*2 (test) + 20*1 (update) + 20*1 (body)  
  B. x = 1, y = 40
  C. No.  The side effect in upper_bound() causes the two to have different
     behaviors with respect to variable x
11.
  ...
  for (i = x; i > x-y; i = i-2)
  ...