Final Exam Solutions
15-213 / 18-213 Fall 2012
01-b 02-a 03-c 04-d 05-a 06-e 07-b 08-a 09-c 10-b
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11-d 12-d 13-b 14-(d or e) 15-c 16-d 17-a 18-b
For 1.14, we allowed e, even though it’s not strictly true, because if
appears in the lecture notes and textbook.
| A | B
Three | 0 100 10 | 0 10 100 Exact in both formats
7/8 | 0 010 11 | 0 00 111 Exact in both formats, norm in A, denorm in B
15/8 | 0 100 00 | 0 01 111 Format A round to even, format B exact
3 pts each, 1/2 credit if reversed
int loop (int a[], int n) {
int i, sum;
sum = 0; // 1pt
for (i = 0; i < n; i++) { //3 pts
sum += a[i]/4; // 3pts
sum += (a[i] < 0 ? a[i] + 3 : a[i]) >> 2;
return sum; //1 pt
Negative integers must be biased before using shift right to divide by
a power of two
Stack The diagram starts with the
addresss arguments for foo()
+———————————–+
0xffffd830| 4 |
+———————————–+
0xffffd82c| caller ra: 0x080483e6 |
+———————————–+
0xffffd828| old ebp: 0xffffd848 |
+———————————–+
0xffffd824| ebx |
+———————————–+
0xffffd820| 3 |
+———————————–+
0xffffd81c| caller ra: 0x80483be |
+———————————–+
0xffffd818| old ebp: 0xffffd828 | <- %ebp = 0xffffd818
+-----------------------------------+
0xffffd814| ebx (or 4) |
+-----------------------------------+
0xffffd810| 2 | <- %esp = 0xffffd810
+-----------------------------------+
a=5 b=2 c=4
2 pts each
2pts correct, -1 incorrect, 0 blank
Part 1. Not graded. Only there to help you organize your work
A: VPN: [19-10] VPO: [9-0]
TLBT: [19-13] TLBI: [12-10]
B: PPN: [17-10] PPO: [9-0]
//Part A not graded. Provided to help you organize your work
Address: 078E6
A: 0000 0111 1000 1110 0110
B: VPN: 01E //5 pts
TLBT: 03
TLB hit? N
page fault? N
C: 01 0101 1100 1110 0110 //1 pt
Address: 04AA4
A: 0000 0100 1010 1010 0100
B: VPN: 012 //5 pts
TLB hit? Y
page fault? N
C: 01 1010 0010 1010 0100 //1 pt
**********
Problem 10
**********
A. No, each thread has its own heap variable for myid.
B. Yes, both threads can point to myid.
C. No, myid is passed in on the stack.
D. Yes, the mutex doesn't protect myid.
E. No, the mutex protects the assignment of myid.
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