Lecture 8: Bitwise Operations in C and UNIX

Question 1

Btiwse AND operator

Answer 1

&

Question 2

How to mask something with 0s?

Answer 2

Bitwise AND.

Question 3

Bitwise assignmetn

Answer 3

Example: AND
x &= int;

Question 4

Octal format specifer.

Answer 4

%o

Question 5

Bitwise OR operator

Answer 5

|

Question 6

XOR operator

Question 7

XOR to swap 2 variables

Answer 7

i1 ^= i2
i2 ^= i1
i1 ^= i2
This lets i1 and i2 be swapped without a temporary variable

Question 8

What does ~ do?

Answer 8

Ones complement

Question 9

Ones complement operator

Answer 9

~

Question 10

Left and right shift operators.

Answer 10

&laquo_space;and&raquo_space;
As I recall, A«B would shift A left by B bits

Question 11

Does left and right shift work with assignment?

Answer 11

Yes.
A«=1;

Question 12

Multiplying/dividing by 2 with bit shifts.

Answer 12

Shift left to multiply by 2.
Shift right to multiply by 2.
Also could be extended to all powers of 2.

Question 13

Arithmetic vs Logical right shift.

Answer 13

If there is a 0 in the left-most bit, it is always filled with a 0. If there is a 1, arithmetic fills with 1s but logical fills with 0s. This varies from machine to machine, so never assume which behavior will be used there.

Question 14

What happens if you try to bit-shift by a negative amount?

Answer 14

Undefined behavior.

Question 15

How might you find if something is a power of 2 with bitwise operators?

Answer 15

Figure it out.