Conditional Processing

Question 1

AND operation betweent he pair of the matching bits in the two operands:

Answer 1

AND destination, source

NOTE: 1-T and 0-F

Question 2

OR operation between the pair of matching bits in two operands:

Answer 2

OR destination, source

NOTE: 1-T and 0-F

Question 3

XOR operation between the pair of matching bits in two operands:

Answer 3

XOR destination, source

NOTE: 0 & 0 = 0; 1 & 1 = 0

Question 4

NOT operation on a single destination operand:

Answer 4

NOT destination

Question 5

Bit- Mapped Sets

Answer 5

Binary bits indicate set membership; Efficient use of storage; Also known as bit vectors. It is like creating a bijection from the indices to the elements, where there is no necessity to convert to/from bit representation of the set from the universal set.

Question 6

Is the bit mapped set in the assembly language use the bitwise operations to manipulate the individual bits within a binary word or a memory location?

Answer 6

Yes, it is true. This help sus in the storage management as in computer graphics, where each bits corresponds to each pixel, the bit is used to store the state of the pixel rather than byte. There are fast operations such as AND, OR and other which are used to cmbine the images if needed.
Bit vecotr here generally refers to the use of the fixed size array of bits to represent a collection of elements.

Question 7

ASCII character ‘a’

Answer 7

97

Question 8

ASCII character ‘A’

Answer 8

65

Question 9

Which bit is cleared out to convert the lowercase a into uppercase A, in the AL register:

Answer 9

bit 5

Question 10

0-9 (ASCII):

Answer 10

48-57

Question 11

How can you turn the caps lock on using the operation OR?

Answer 11

Set the bit 6;

mov ax, 40h; loads the segment address of the the BIOS data area into ax
mov ds, ax; Set the ds to BDA segment
mov bx, 17h; Load the offset of the keyboard flag into the bx
or BYTE PTR [bx], 01000000; Turn on the caps lock key

Question 12

Jump to a label if the integer is even?

Answer 12

mov ax, wordVal
add ax, 1
jz EvenVals

If the Zero flag is set, jump to the label.

Question 13

LSB

Answer 13

the right most bit

not set LSB == zero flag set => jump to the even value, and vice-versa

Question 14

If the integer is negative

Answer 14

cmp ax, 0
jl Negative Val

Question 15

Jump to a label if the value in AL is not zero:

Answer 15

or al, al
jnz IsNotZero

Question 16

Does Oring a number with itself chnages its value?

Answer 16

No

Question 17

Test Instruction perform a bitwise AND operation between two operands (hence, non destructive), but____________

Answer 17

it does not stores the result. It just update the flag register based on the result.

NOTE: test al, 00000001b
jnz ValueNotFound

Question 18

CMP instruction:

Answer 18

comapres the destination operand to the source operand. Non destructive subtraction of the spurce from the destination. It does not chnage th evalue in the destination.

Question 19

Is the sign flag equal to the overflow flag in the given instructions below?

mov al, -1
cmp al, 5

Answer 19

No

Question 20

Jcond Instruction:

Answer 20

A Jcond branches to a label when the specific flag or registers conditions are met.

Question 21

JB, JC

Answer 21

Jump to a label, When the carry flag is set

Question 22

JE, JZ

Answer 22

jump to the label when the zero flag is set

Question 23

JNE, JNZ

Answer 23

jump to the label when the zero flag is clear

Question 24

JS

Answer 24

jump to the label when the sign flag is set

Question 25

JECXZ

Answer 25

jump to a label if the ECX=0

Question 26

Prior to 386, jump must be within _________ from current counter location.

Answer 26

-128 to +127 byte

Question 27

In x86 processors, __________ permits jum[ anywhere in the memory.

Answer 27

32-bit offset

Question 28

Jump is based on specific flags, equality, signed and unsigned operands

Answer 28

Yes, thats correct!

Question 29

JE

Answer 29

jump if equal

Question 30

JCXZ

Answer 30

jump if CX=0, where CX is the loop counter for 16-bit, ECX for 32-bit & RCX is the 64-bit

Question 31

JA

Answer 31

jump if above, leftop>rightop

Question 32

JNBE

Answer 32

jump if not below or equal

Question 33

JAE

Answer 33

jump if above or equal , leftop >= rightop

Question 34

JNB

Answer 34

same as JAE

Question 35

JB

Answer 35

jump if below, leftop<rightop

Question 36

JNAE

Answer 36

same as JB

Question 37

JBE

Answer 37

jump if below or equal

Question 38

JNA

Answer 38

same as JBE

Question 39

JG, JNLE

Answer 39

jump if greater, leftop>rightop

Question 40

JGE, JNL

Answer 40

Jump if greater than or equal

Question 41

JL, JNGE

Answer 41

jump if less than

Question 42

JLE, JNG

Answer 42

jump if less than or equal to

Question 43

Application: Jump to a label if the signed EAX is greater than EBX
HOw would you write the code snippet for this?

Answer 43

cmp eax, ebx
jg Greater

Question 44

What is the code snippet for the jump to the label L1 if the memory word pointed by the ESI equals zero?

Answer 44

cmp WORD PTR [esi], 0
je L1

Question 45

Jump to the label L1 if the bits 0,1, &3 are set all in AL:

Answer 45

and AL, 00001011b
cmp al, 00001011b
je L1

Question 46

Encrypting a string code snippet

Answer 46

KEY =239
BUFFMAX=128
.data
buffer BYTE BUFMAX+1 DUP (0)
buffSize DWORD BUFMAX

.code
mov ecx, buffSize
mov esi, 0
L1:
xor buffer[esi], KEY
inc esi
loop L1

Question 47

BT Instrcution

Answer 47

Copies bit n from the operand into the carry flag for the bit test.

BT bitBase, n
bitBase is r/m 16; r/m32
n is r16; r32; imm8

Question 48

LOOPZ and LOOPE

Answer 48

LOOPZ destination
LOOPE destination

Logic:
ECX<- ECX -1
if ECX >0 and ZF=1, jump to the destination

Useful for scanning the first element that does not match the given element in array

Question 49

LOOPNE and LOOPNZ

Answer 49

LOOPNE destination
LOOPNZ destination

if ECX >0 and ZF=0, jump to destination

Useful when scanning the first element that matches the given value

Question 50

Conditional Structures

Answer 50

Block-Structured IF statements; Compund Expression with AND (use short circuit evaluation: without evaluating each and every part); compund Expression with OR (short circuit evaluation); Table driven selection (uses a table lookup to replace the multiway selction structure- create a table for the lookup values and the offsets of labels or procedures and use a loop to search the table)

Question 51

call NEAR PTR [ebx+1]

Answer 51

call the procedure for the procedure pointers requirement.