Bit Manipulation And Bitwise

Question 1

Bit manipulation

Answer 1

Modifying individual bits within an object, used for encription and compression algorithm

Question 2

Bit flags

Answer 2

Bits when individual bits of an object are used as boolean values

Question 3

A flag

Answer 3

In computing, a value that acts as a signal for some function or process

Question 4

Defining a set of bit flags

Answer 4

Using unsigned integer of the apropriatesize depending on how many flags we have or std::bitset

Question 5

Bit numbering

Answer 5

In a sequence we number the bits from right to left starting with 0, each number denotes bit position

Question 6

Functions that are useful for bit manipulation

Answer 6

Std::bitset provides 4

• test()
• set()
• reset()
• flip()

Question 7

Test()

Answer 7

Allows us to qmuery whether a bit is a 0 or 1

Question 8

Set()

Answer 8

Allows us to turn a bit on

Question 9

Reset()

Answer 9

Allows us to turn a bit off

Question 10

Flip()

Answer 10

Allows us to flip a bit value from 0 to 1 and vice versa

Question 11

Bitwise operators

Answer 11

Bot manipulation operators

<>,~,&,| and ^

Question 12

Bitwise left shift

Answer 12

Shifts bits to the lef, lefto operand is the expression to shift the bits of, right operand is integer number of bits to shift left by x«1, new bits recieve value 0

Question 13

Bitwise right shift&raquo_space;

Answer 13

Shifts bits to the right

Question 14

Operators &laquo_space;and&raquo_space;

Answer 14

Are used for output and input

Question 15

Overloaded

Answer 15

Provided an alternative definition for operator

Question 16

Bitwise NOT ~

Answer 16

Flips each bit from 0 to 1 and vice versa, the result is dependent on the size of the data type

Question 17

Bitwise OR |

Answer 17

Works lige logical or, but instead of aapplying the or to the operand it applise it to each bit, evaluates 1 if eather left, right or both bits are 1, 0 otherwise

Question 18

Bitwise AND &

Answer 18

Evaluates to true 1 if both bits in the column are 1

Question 19

Bitwise XOR ^

Answer 19

Exclusive, or evaluates true if one and only one operand is true, if neither or both are true it evaluates to 0, in compound expressions if there is an odd number of 1 bits the result is true, even number is false

Question 20

Bitwise assignment operators

Answer 20

«=,&raquo_space;=, |=, &=, ^=

Instead x=x»1, you can write x»=1

Question 21

Bit mask

Answer 21

Predefined set of bits that is used to select wich specific bits will be modified by subsequent operator

Question 22

Simplest set of bit mask

Answer 22

To define one bit mask for each bit position, defined as symbolic constants to be reused

Question 23

Testing a bit

Answer 23

Use a bit mask in conjunction with a bit flag variable

Question 24

Setting a bit

Answer 24

Use a bit mask in conjunction with bitwise or equals =

Question 25

Resetting a bit

Answer 25

We use bitwise and bitwise not

Question 26

Flipping a bit

Answer 26

We use bitwise XOR

Question 27

Bit masks and std::bitset

Answer 27

The functions alloes us to modify individual bits, the operators to modify multiple bits at once

Question 28

Use for bit flags

Answer 28

• when you have many identical flag variables
• when you have a function that can take any combinations of 32 different options
• to pass in only the options you wanted

Question 29

Binary numbers

Answer 29

Work like decimals, because there are only 2 binary digits, the value of each digit increases by factor of 2

Question 30

Converting binary to decimal

Answer 30

8 bit number 0101 1110 is (0×128)+(1×64)+(0×32)….=94

Question 31

Converting decimal to binary

Answer 31

2 methods
* dividing by 2 and writing down the remainders, the binary number is constructed from the remainders from the bottom up
* 148 largest power of 2 thats smaller than 148=128
148>=128 yes, 128 bit is 1, 148-128=20
20>=64 no, 64 bit is 0…

Question 32

Adding in binary

Answer 32

0110 + 0111= 0+1=1, 1+1=0 carried 1, 1+1=0+1carreid =1, 0+0=0

Question 33

Two’s complement

Answer 33

Method for storing signed integers

Question 34

Positive signed numbers

Answer 34

Represented in binary just like positive unsigned numbers, with sign bit of 0

Question 35

Negative signed numbers

Answer 35

Represented in binary as the bitwise inverse of the positive number +1

Question 36

Converting integers to binary two’s complement

Answer 36

5 in binary is 0000 0101, inverted is 1111 1010, we add 1=1111 1011

Question 37

Why we add 1 to convert integer to binary two’s complement

Answer 37

If we only inverse it 0 will have 2 representations 0000 0000 and 1111 1111 so we add 1 to overflow

Question 38

Converting binary two’s complement to integers

Answer 38

We look at the sign bit, if it is 0 we convert the numbers as unsigned, if it is 1 we invert the bits, add 1, convert to decimal, make the decimal negative

Question 39

Why tipes matter

Answer 39

If it is unsigned it can store numbers of values, but if it is signed it can only store half of that number.