7.9: Exercises

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Below are some quiz questions and suggested projects based on this chapter.

Questions

Below are some quiz questions based on this chapter.

1) Which of the following instructions is legal / illegal? As appropriate, provide an explanation.

1. mov     rax, 54
2. mov     ax, 54
3. mov     al, 354
4. mov     rax, r11
5. mov     rax, r11d
6. mov     54, ecx
7. mov     rax, qword [qVar]
8. mov     rax, qword [bVar]
9. mov     rax, [qVar]
10. mov    rax, qVar
11. mov    eax, dword [bVar]
12. mov    qword [qVar2], qword [qVar1]
13. mov    qword [bVar2], qword [qVar1]
14. mov    r15, 54
15. mov    r16, 54
16. mov    r11b, 54

2) Explain what each of the following instructions does.

1. movzx     rsi, byte [bVar1]
2. movsx     rsi, byte [bVar1]

3) What instruction is used to:

convert an unsigned byte in al into a word in ax.
convert a signed byte in al into a word in ax.

4) What instruction is used to:

convert an unsigned word in ax into a double-word in eax.
convert a signed word in ax into a double-word in eax.

5) What instruction is used to:

convert an unsigned word in ax into a double-word in dx:ax.
convert a signed word in ax into a double-word in dx:ax.

6) Explain the difference between the cwd instruction and the movsx instructions.

7) Explain why the explicit type specification (dword in this example) is required on the first instruction and is not required on the second instruction.

1. add    dword [dVar], 1
2. add    [dVar], eax

8) Given the following code fragment:

    mov    rax, 9
    mov    rbx, 2
    add    rbx, rax

What would be in the rax and rbx registers after execution? Show answer in hex, full register size.

9) Given the following code fragment:

    mov    rax, 9
    mov    rbx, 2
    sub    rax, rbx

What would be in the rax and rbx registers after execution? Show answer in hex, full register size.

10) Given the following code fragment:

    mov    rax, 9
    mov    rbx, 2
    sub    rbx, rax

What would be in the rax and rbx registers after execution? Show answer in hex, full register size.

11) Given the following code fragment:

    mov    rax, 4
    mov    rbx, 3
    imu1   rbx

What would be in the rax and rdx registers after execution? Show answer in hex, full register size.

12) Given the following code fragment:

    mov    rax, 5
    cqo
    mov    rbx, 3
    idiv   rbx

What would be in the rax and rdx registers after execution? Show answer in hex, full register size.

13) Given the following code fragment:

          mov   rax, 11
          cqo
          mov   rbx, 4
          idiv  rbx

What would be in the rax and rdx registers after execution? Show answer in hex, full register size.

14) Explain why each of the following statements will not work.

    1. mov    42, eax
    2. div    3
    3. mov    dword [num1], dword [num1]
    4. mov    dword [ax], 800

15) Explain why the following code fragment will not work correctly.

          mov    eax, 500
          mov    ebx, 10
          idiv   ebx

16) Explain why the following code fragment will not work correctly.

          mov   eax, -500
          cdq
          mov    ebx, 10
          div    ebx

17) Explain why the following code fragment will not work correctly.

          mov    ax, -500
          cwd
          mov    bx, 10
          idiv   bx
          mov    dword [ans], eax

18) Under what circumstances can the three-operand multiple be used?

Suggested Projects

Below are some suggested projects based on this chapter.

1) Create a program to compute the following expressions using unsigned byte variables and unsigned operations. Note, the first letter of the variable name denotes the size (b → byte and w → word).

Use the debugger to execute the program and display the final results. Create a debugger input file to show the results in both decimal and hexadecimal.

bAns1 = bNum1 + bNum2
bAns2 = bNum1 + bNum3
bAns3 = bNum3 + bNum4
bAns6 = bNum1 – bNum2
bAns7 = bNum1 – bNum3
bAns8 = bNum2 – bNum4
wAns11 = bNum1 * bNum3
wAns12 = bNum2 * bNum2
wAns13 = bNum2 * bNum4
bAns16 = bNum1 / bNum2
bAns17 = bNum3 / bNum4
bAns18 = wNum1 / bNum4
bRem18 = wNum1 % bNum4

2) Repeat the previous program using signed values and signed operations. Use the debugger to execute the program and display the final results. Create a debugger input file to show the results in both decimal and hexadecimal.

3) Create a program to complete the following expressions using unsigned word sized variables. Note, the first letter of the variable name denotes the size (w → word and d → double-word).

wAns1 = wNum1 + wNum2
wAns2 = wNum1 + wNum3
wAns3 = wNum3 + wNum4

wAns6 = wNum1 – wNum2
wAns7 = wNum1 – wNum3
wAns8 = wNum2 – wNum4
dAns11 = wNum1 * wNum3
dAns12 = wNum2 * wNum2
dAns13 = wNum2 * wNum4
wAns16 = wNum1 / wNum2
wAns17 = wNum3 / wNum4
wAns18 = dNum1 / wNum4
wRem18 = dNum1 % wNum4

Use the debugger to execute the program and display the final results. Create a debugger input file to show the results in both decimal and hexadecimal.

4) Repeat the previous program using signed values and signed operations. Use the debugger to execute the program and display the final results. Create a debugger input file to show the results in both decimal and hexadecimal.

5) Create a program to complete the following expressions using unsigned double- word sized variables. Note, the first letter of the variable name denotes the size (d → double-word and q → quadword).

dAns1 = dNum1 + dNum2
dAns2 = dNum1 + dNum3
dAns3 = dNum3 + dNum4
dAns6 = dNum1 – dNum2
dAns7 = dNum1 – dNum3
dAns8 = dNum2 – dNum4
qAns11 = dNum1 * dNum3
qAns12 = dNum2 * dNum2
qAns13 = dNum2 * dNum4
dAns16 = dNum1 / dNum2
dAns17 = dNum3 / dNum4

12. dAns18 = qNum1 / dNum4

13. dRem18 = qNum1 % dNum4
Use the debugger to execute the program and display the final results. Create a

debugger input file to show the results in both decimal and hexadecimal.

6) Repeat the previous program using signed values and signed operations. Use the debugger to execute the program and display the final results. Create a debugger input file to show the results in both decimal and hexadecimal.

7) Implement the example program to compute the sum of squares from 1 to n. Use the debugger to execute the program and display the final results. Create a debugger input file to show the results in both decimal and hexadecimal.

8) Create a program to compute the square of the sum from 1 to n. Specifically, compute the sum of integers from 1 to n and then square the value. Use the debugger to execute the program and display the final results. Create a debugger input file to show the results in both decimal and hexadecimal.

9) Create a program to iteratively find the nth Fibonacci number(For more information, refer to: http://en.Wikipedia.org/wiki/Fibonacci_number). The value for n should be set as a parameter (e.g., a programmer defined constant). The formula for computing Fibonacci is as follows:

\[fibonacci(n) = \begin{cases} n & \text{if } n = 0 \text{ or } n = 1 \\ fibonacci (n - 2) + fibonacci (n - 1) & \text{if } n \ge 2 \end{cases}\nonumber\]

Use the debugger to execute the program and display the final results. Test the program for various values of n. Create a debugger input file to show the results in both decimal and hexadecimal.