CS305 Final Exam Questions

CS305 Final Exam

Date: 10:00-11:50AM, 12/16/2014. Name: Steven Centino Score: ________

I. Multiple-Choice (30%, 2% for each question)
1. (D) Which of the following CALL instructions writes the contents of EAX to standard output as a signed decimal integer?
a. call WriteInteger b. call WriteDec c. call WriteHex d. call WriteInt
2. (A) Which of the following are true about the PUSH instruction?
a. It decrements the stack pointer (by 2 or 4) and copies the operand into the stack at the location pointed to by the stack pointer.
b. It copies the operand into the stack at the location pointed to by the stack pointer, and then decrements the stack pointer (by 2 or 4).
c. It increments the stack pointer (by 2 or 4) and copies the operand into the stack at the location pointed to by the stack pointer.
d. It increments the stack pointer by 1 and copies the operand into the stack at the location pointed to by the stack pointer.
3. (A) What will be the hexadecimal value of AL after these instructions execute? mov al,0CFh and al,2Bh
a. 0Bh b. EAh c. 06h d. none of the above
4. (C) What will be the hexadecimal value of AL after these instructions execute? mov al,3Ch or al,82h
a. 3Eh b. BCh c. BEh d. none of the above
5. (B) What will be the hexadecimal value of AL after these instructions execute? mov al,94h xor al,37h
a. B7h b. A3h c. 3Fh d. none of the above
6. (A&D) Which answer choice shows the correct values of the Carry, Zero, and Sign flags after the following instructions execute? mov al,6 cmp al,5
a. CF = 0, ZF = 0, SF = 0 b. CF = 1, ZF = 0, SF = 0
c. CF = 1, ZF = 1, SF = 0 d. CF = 1, ZF = 0, SF = 1
7. (B) Suppose EAX, EBX, and ECX contained three unsigned integers. Which of the following code excerpts would display the largest of the three integers?
a.
cmp eax,ebx jb L1 mov eax,ebx
L1: cmp eax,ecx jb L2 mov eax,ecx
L2: call WriteInt
b.
cmp eax,ebx jae L1 mov eax,ebx
L1: cmp eax,ecx jae L2 mov eax,ecx
L2: call WriteInt
c.
cmp eax,ebx jnae L1 mov eax,ebx
L1: cmp ecx,eax jnae L2 mov eax,ecx
L2: call WriteInt
d.
cmp eax,ecx jae L1 mov eax,ebx
L1: cmp eax,ebx jae L2 mov eax,ecx
L2: call WriteInt
8. ( ) What will be the final value of ESI when the following code executes?
.data
array SWORD 8,2,3,5,-4,6,0,4
.code
mov esi,0 mov ecx,LENGTHOF array
L1: mov ax,array[esi] cmp ax,0 pushf add esi,TYPE array popf Loopne L1
a. 00000006h b. 00000007h c. 0000000Ch d. 0000000Eh
9. ( ) What will be the final values of CX and DX when the following code executes?
.data
array SWORD 8,2,3,5,-4,6,0,4
.code
mov cx,1 mov esi,2 mov ax,array[esi] mov bx,array[esi+4] cmp ax,3 jae L2 cmp bx,4 jb L1 jmp L3
L1: mov cx,4
L2: mov dx,5 jmp L4
L3: mov dx,6
L4:
a. CX = 4, DX = 5 b. CX = 1, DX = 6 c. CX = 1, DX = 5 d. CX = 4, DX = 6
10. (B) Suppose we want to copy the value of the Carry flag into bit 7 of AL, and shift all existing bits in AL one position to the right. Which of the following instructions will work?
a. shr al,1 b. sar al,1 c. ror al,1 d. rcr al,1
11. (B) Which of the following instructions will divide the unsigned integer in EBX by 8?
a. shr ebx,8 b. shr ebx,3 c. sar ebx,8 d. shl ebx,3

12. (C) Which of the following instructions will multiply the integer in EBX by 32?
a. shr ebx,5 b. rol ebx,32 c. shl ebx,5 d. ror ebx,32
13. (C) What will be the hexadecimal values of DX and AX after the following instructions have executed? mov ax,6B49h mov dx,0095h shl ax,1 rcl dx,1
a. DX = 0148h, AX = C691h b. DX = 012Ah, AX = C9A2h
c. DX = 012Ah, AX = D692h d. DX = 024Bh, AX = D692h
14. (B) Which of the following blocks of instructions will multiply the contents of the EDX register by 36?
a.
mov ebx,edx shl edx,5 shl ebx,2 add ebx,edx
b.
mov ebx,edx shl edx,5 shl ebx,2 add edx,ebx
c.
mov ebx,4 add edx,ebx shl edx,2 shl ebx,5 add edx,ebx
d.
mov ebx,edx shl ebx,5 shl edx,2 add edx,ebx
15. ( ) Given that EAX contains FFFF80C0h, which of the following would be true after executing the CWD instruction?
a. AX=FFFFh, DX=80C0h b. EDX=FFFFFFFFh, EAX=FFFF80C0h
c. DX=FFFFh, AX=80C0h d. cannot be determined

II. Short Programming Problems (40%, 10% for each problem)
16. Given the following string definition, write a sequence of statements that write the string to standard output. Use a library procedure. str1 BYTE "I love UOG and Computer Science",0 mov dx, OFFSET str1 call WriteString
17. Write statements that use library procedures to generate a single unsigned pseudorandom integer between 0 and 99 and write it to standard output. mov eax, 100 call RandomRange call WriteDec

18. Write a series of instructions that will multiply EAX by 20, using a combination of shift, MOV, and ADD instructions.
Mov ebx, eax
Shl eax, 4 ;2^4=16
Shl ebx,2 ;2^2=4
Add eax,ebx

19. Write a sequence of instructions that divide 15 by 5, using the IDIV instruction. Use the EBX register as the divisor.
Mov eax, -15
Cdq ; extend eax into edx
Mov ebx, 5
Idiv ebx

III. Assembly Programming (30%).
20. a. Chapter 9.7.2 (page 295): Write a procedure named Str_concat that concatenates a source string to the end of a target string….
b. Use screenshots to show the memory dumps of your source, original target, and concatenated target strings.

Original Target:

Concatenated target strings:

Source Code: