Question

1. What will be the contents of BX after the following instructions execute?

mov bx,5

stc

mov ax,60h

adc bx,ax

2. Describe the output when the following code executes in 64-bit mode:

.data

dividend_hi QWORD 00000108h

dividend_lo QWORD 33300020h

divisor QWORD 00000100h

.code

mov rdx,dividend_hi

mov rax,dividend_lo

div divisor

3. The following program is supposed to subtract val2 from val1. Find and correct all logic

errors (CLC clears the Carry flag):

.data

val1 QWORD 20403004362047A1h

val2 QWORD 055210304A2630B2h

result QWORD 0

.code

mov cx,8 ; loop counter

mov esi,val1 ; set index to start

mov edi,val2

clc ; clear Carry flag

top:

mov al,BYTE PTR[esi] ; get first number

sbb al,BYTE PTR[edi] ; subtract second

mov BYTE PTR[esi],al ; store the result

dec esi

dec edi

loop top

4. What will be the hexadecimal contents of RAX after the following instructions execute in

64-bit mode?

.data

multiplicand QWORD 0001020304050000h

.code

imul rax,multiplicand, 4

Answer 1

1)

The final value will be (5 in bx + 1 for carry+ 60h address)

bx= 0066h

2)

RAX = 0108000000003330

RDX = 0000000000000020

3)

.data

val1 QWORD 2040300 436 2047A1h

val2 QWORD 055210 304A2630B2h

result QWORD 0

. code

mov ecx, 8

mov esi , offset val1

mov edi , offset val2

mov ebx , offset result

clc

top :

mov al, BYTE PTR[esi]

sbb al, BYTE PTR[edi]

mov BYTE PTR [ebx], al

inc esi

inc edi

inc ebx

loop top

4)

RAX = 01000001020304050000