Bit Manipulation

Question 1

operand instruction for logical and

Answer 1

AND

Question 2

operand instruction for logical or

Answer 2

ORR

Question 3

operand instruction for logical not

Answer 3

MVN

Question 4

operand instruction for logical exclusive or

Answer 4

EOR

Question 5

what instruction can be used to set

Answer 5

AND

Question 6

what does set mean

Answer 6

change to 1

Question 7

what does clear mean

Answer 7

change to 0

Question 8

uses for bit manipulation

Answer 8

working with floats]

writing code that controls hardware eg turn on/off LEDS

Question 9

if you have X AND 0 what will this result in

Answer 9

0

Question 10

if you have X AND 1 what will this result in

Answer 10

X

Question 11

if we want to clear bits in positions 3 and 4, what do we do

Answer 11

use AND

with a mask which contains all 1s and only 0s in the positions we want to clear

Question 12

what does the BIC function do

Answer 12

clears with the mask we have already defined

Question 13

if we want to set bits in positions 3 and 4, what do we do

Answer 13

use ORR

with a mask which contains all 0s and only 1s in the positions we want to set

Question 14

if you have X OR 1 what will this result in

Answer 14

1

Question 15

if you have X OR 0 what will this result in

Answer 15

0

Question 16

what function can be used to invert certain bits

Answer 16

EOR

Question 17

if we want to invert bits in positions 3 and 4, what do we do

Answer 17

use EOR,

with a mask with 1s in the positions we want to invert and 0s everywhere else

Question 18

how can bit manipulation be used for difference between upper and lower case letters

Answer 18

only difference between upper and lower case letters is the 6th bit (because 0x20 difference)

we can convert to upper case by clearing 6th bit
we can convert to lower case by setting 6th bit

Question 19

what instruction is used for a logical shift left

Answer 19

LSL

Question 20

when a 32 bit is shifted to the left where does the MSB go

Answer 20

discarded

Question 21

when a 32 but is shifted to the left what does the LSB change to

Answer 21

0

Question 22

by how many bit positions can you shift

Answer 22

from 0 to 31

Question 23

Logical shift left is the same as

Answer 23

Multiplying by 2n.

An effective way to perform multiplication by powers of 2

Question 24

what instruction is used for logical shift right

Answer 24

LSR

Question 25

what is the MSB set to in a logical shift right

Answer 25

0

Question 26

what happens to the least significant byte in a logical shift right

Answer 26

gets discarded

Question 27

logical shift right is the same as

Answer 27

dividing by 2n

Question 28

general formula for logical shifts

Answer 28

MOV Rd, Rm, LSR/L #n

Question 29

how can we not discard the bit when performing logical shifts

Answer 29

by using the MOVS instruction to store the bit in the carry flag

Question 30

what does BCC instrutcion do

Answer 30

branch if carry clear (0)

Question 31

What does the BCS instruction do

Answer 31

branch if carry set (1)

Question 32

how to perform right and left shifts on signed values ie to keep the msb the same (as it represents the sign)

Answer 32

use the ASR instruction

Question 33

What instruction can be used to rotate to the right

Answer 33

ROR #n

Question 34

what instruction can be used to rotate to the left

Answer 34

ROR #32-n

Question 35

formula for rotating right

Answer 35

MOV Rd, Rm, ROR #n