CSci250 Assembly Language Programming: Homework 3 Solutions

CSci250 Assembly Language Programming: Homework 3 Solutions
Due date: Friday, October 31, 2008 in class
Each homework may have a different weight, which depends on its level of difficulty.
Absolutely no copying others' work

Error

     .data
     var1  SBYTE  -5, -2, -1, 1
     var2  WORD   0A01h, 8h, 0Bh, 200h
     var3  SWORD  3, -4
     var4  DWORD  8, 7

What will be the hexadecimal value of the destination operand after each of the following instructions executes in sequence? (10%)
```
     mov  ax, var3-1             ; a. ax = 0302h

     mov  ah, var2-2             ; b. ah = Error
```

What will be the value of the destination operand after each of the following instructions executes in sequence? (10%)
```
     movzx  edx, var2-1          ; b. edx =  00000101h

     movsx  edx, [var3+1]        ; d. edx = 0FFFFFC00h
```

Where indicated, write down the values of the Carry, Sign, Zero, Overflow, and Parity flags after each instruction has executed: (20%)

    mov  ax, 00FFh
    sub  ah, 1        ; CF = 1    SF = 1    ZF = 0    OF = 0    PF = 1


    neg  ah           ; CF = 1    SF = 0    ZF = 0    OF = 0    PF = 0


    add  al, 1        ; CF = 1    SF = 0    ZF = 1    OF = 0    PF = 1

Write a sequence of two instructions that set both the Overflow and Sign flags, but not Carry flag. (16%)
Ans>

    .data
    data1   LABEL  BYTE
    data2   WORD   10h, 5+2, 10
    array   DWORD  10 DUP (20 DUP(?)))
    string  BYTE   'a', 'b', 'c', 0

Indicate the value of EAX after each instruction executes: (16%)

    mov  eax, TYPE data1           ; EAX = 1
    mov  eax, LENGTHOF data1       ; EAX = 1
    mov  eax, SIZEOF data1         ; EAX = 1
    mov  eax, TYPE data2           ; EAX = 2
    mov  eax, LENGTHOF data2       ; EAX = 3
    mov  eax, SIZEOF data2         ; EAX = 6
    mov  eax, TYPE array           ; EAX = Error or 4 if the extra ) is not there
    mov  eax, LENGTHOF array       ; EAX = Error or 200 if the extra ) is not there
    mov  eax, SIZEOF array         ; EAX = Error or 800 if the extra ) is not there 
    mov  eax, TYPE string          ; EAX = 1
    mov  eax, LENGTHOF string      ; EAX = 4
    mov  eax, SIZEOF string        ; EAX = 4

    myBytes1    BYTE   -2, 10, 20
    myWords1    WORD   30h, 0Ah
    myDoubles1  DWORD  1030h, 120h
    myPointer1  DWORD  myBytes1

Fill in the requested register values on the right side of the following instruction sequence: (16%)

     mov  esi, OFFSET myWords1
     mov  eax, DWORD PTR [esi+3]         ; EAX = 00103000h

     mov  ax,  WORD PTR myBytes1 + 2     ;  AX =     3014h

     mov  esi, myPointer1
     mov  eax, DWORD PTR [esi]           ; EAX = 30140AFEh

     mov  ax,  WORD PTR [esi+4]          ;  AX =     0A00h

What will be the final value of EAX in this example? (12%)

     mov   eax, 0
     mov   ecx, 2
 L1: mov   ebx, ecx
     mov   ecx, 2  
 L2: jmp   L4
 L3: inc   eax
     loop  L2
     mov   ecx, ebx
     loop  L1
 L4: jmp   L3

Ans>

Error