Binary Arithmetic

Question 1

What is a carry

Answer 1

when we run out of digits for storage, a carry will store the last digit

Question 2

what is the amount of bits we are limited to in our arm architecture

Answer 2

32

Question 3

What is the largest number we can represent with 32 bits

Answer 3

2^32

Question 4

What are the four condition control flags

Answer 4

Negative
Overflow
Zero
Carry

Question 5

what does the carry flag let us know

Answer 5

that the register does not store the actual answer as it was too big to be stored

Question 6

how do we tell the processor to update the condition code flags

Answer 6

using s-bit. eg. ADDS, MOVS,

Question 7

If s bit is set to 0 what does this mean

Answer 7

the condition code fags did not need to be set (false)

Question 8

If s bit is set to 1 what does this mean

Answer 8

the condition code fags needed to be set (true)

Question 9

how does the processor remember the results of the compare instruction

Answer 9

by updating the condition code flags

Question 10

example of everyday modulo arithmetic

Answer 10

12 hour clock

Question 11

modulo arithmetic used in binary

Answer 11

twos complement

Question 12

how does twos complement work

Answer 12

the second half of the binary pattern is used again to represent minus numbers. Which way we see it should be from our interpretation of the numbers as the computer doesn’t know whether we are choosing a signed or unsigned interpretation

Question 13

if the interpretation is negative, what is the most significant bit

Answer 13

1

Question 14

if the interpretation is positive, what is the most significant bit

Answer 14

0

Question 15

how to represent a minus number

Answer 15

1. get positive version in binary
2. invert
3. add 1

Question 16

what does it mean to invert

Answer 16

changing all 0s to 1s and all 1s to 0s

Question 17

Why does the method we use for changing a binary number to it’s negative version work

Answer 17

inverting the bits is the equivalent of subtracting from minus 1, so that is why we add the 1 on at the end as if we were taking it away from 0

Question 18

what is the operation used for inverting

Answer 18

MVN

Question 19

what does MVN stand for

Answer 19

move with not

Question 20

what operation is used to get the negative version of a number

Answer 20

NEG

Question 21

what does NEG stand for

Answer 21

negate

Question 22

what does NEG really do

Answer 22

RSB R0, R0 , #0, when number is stored in r0

Question 23

technically, why doesnt the processor need to know the method of subtraction

Answer 23

As long as it can do addition and change signs, subtraction can be done

Question 24

What is oveflow

Answer 24

when the result of addition or subtraction gives a result that is outside of the signed number system

Question 25

what flag if used for overflow

Answer 25

V

Question 26

why is V used for overflow instead of O

Answer 26

as to not confuse the zero and overflow flags

Question 27

what flag is used for carry

Answer 27

C

Question 28

What are the overflow rules, when will it occur that v=1

Answer 28

when the MSB(a)=MSB(b) and MSB(a)=MSB(result)

Question 29

what does MSB stand for

Answer 29

most significant bit

Question 30

`What falg is used for 0

Answer 30

zero flag

Question 31

when will 0 flag be set to 1

Answer 31

when the result is all 0

Question 32

what flag is used for negatives

Answer 32

N

Question 33

When will the n flag be set to 1

Answer 33

is the result is negative (MSB=1)

Question 34

how many binary digits are behind each hex digit

Answer 34

4