Bitwise Manipulation

Test yourself

Bitwise Manipulation - Shifts

Bitwise manipulation is the act of modifying data by changing the bits within individual bytes.

Logical shift right

A logical shift right moves each of the bits in a byte one place to the right.
The ‘least significant bit’ (LSB) on the right is lost and the empty space for the ‘most significant bit’ (MSB) is filled with a ‘0’.
- For example, 1 0 1 0 1 0 0 0 $\rightarrow$ 0 1 0 1 0 1 0 0
A logical shift right is identified with a triple chevron ‘>>>’.

Logical shift left

A logical shift left moves each of the bits in a byte one place to the left.
The MSB on the left is lost and the empty space for the LSB is filled with a ‘0’.
- For example: 1 0 1 0 1 0 0 0 $\rightarrow$ 0 1 0 1 0 0 0 0
A logical shift left is identified with a ‘<<<’.

Arithmetic shift right

Arithmetic shifts are almost the same as logical shifts, except the MSB is a sign bit and always remains the same.
An arithmetic shift right has the following result:
- 1 0 1 0 1 0 0 0 $\rightarrow$ 1 0 0 1 0 1 0 0
- This has the effect of dividing the original number by 2.
An arithmetic shift right is identified with a '>>'.

Arithmetic shift left

An arithmetic shift left has the following result:
- 1 0 1 0 1 0 0 0 $\rightarrow$ 1 1 0 1 0 0 0 0
- This has the effect of multiplying the original number by 2.
An arithmetic shift left is identified with a '<<'.

Circular shift

With a right circular shift, the same procedure applies.
However, instead of losing the LSB in a right shift, it ‘wraps around’ and becomes the MSB.
- 1 0 1 0 1 0 0 0 $\rightarrow$ 0 1 0 1 0 1 0 0
Similarly, with a left circular shift, the MSB becomes the new LSB.
- 1 0 1 0 1 0 0 0 $\rightarrow$ 0 1 0 1 0 0 0 1

Bitwise Manipulation - Masks

Bitwise manipulation is the act of modifying data by changing the bits within individual bytes.

Masks

Masks can be used with binary numbers to extract, set or toggle certain bits within a byte.
The following examples use the mask 1 1 1 1 0 0 0 0.

Illustrative background for AND ?? "content

AND

The AND operation extracts whichever bits of the byte correspond to the 1s in the mask. The bits that correspond to 0 are returned as 0.
For example, our AND mask extracts just the first four bits of a byte:
- Original byte: 1 0 1 1 1 0 0 1
- AND Mask: 1 1 1 1 0 0 0 0
- Result: 1 0 1 1 0 0 0 0

Illustrative background for OR ?? "content

OR

The OR operation sets digits equal to 1 (for bits corresponding to the 1s in the mask) or leaves them unchanged (for bits corresponding to the 0s in the mask).
For example, our OR mask sets the first four bits of a byte to ‘1’:
- Original byte: 1 0 1 1 1 0 0 1
- OR Mask: 1 1 1 1 0 0 0 0
- Result: 1 1 1 1 1 0 0 1

Illustrative background for XOR ?? "content

XOR

The XOR operation toggles binary digits (for bits corresponding to the 1s in the mask) or leave them unchanged (for bits corresponding to the 0s in the mask).
For example, our XOR mask toggles the first four bits of a byte:
- Original byte: 1 0 1 1 1 0 0 1
- XOR Mask: 1 1 1 1 0 0 0 0
- Result: 0 1 0 0 1 0 0 1

1Components of a Computer

1.1Structure & Function of the Processor

1.1.1Structure of the CPU

1.1.2Fetch, Decode, Execute Cycle

1.1.3Factors Affecting CPU Performance

1.1.4CPU Architecture

1.2Types of Processors

1.2.1CISC & RISC

1.2.2Multicore & Parallel Cores

1.3Input, Output & Storage

1.3.1Computer Systems

1.3.2Magnetic Storage

1.3.3Optical Storage

1.3.4Types of Optical Storage

1.3.5Types of Memory

1.3.6Flash Memory

1.3.7Virtual Memory

2Software & Software Development

3Exchanging Data

4Data Types, Data Structures & Algorithms

4.1Data Types

4.1.1Data Types

4.1.2Arrays & Strings

4.1.3Representing Numbers

4.1.4Binary Arithmetic

4.1.5Hexadecimal

4.1.6Converting Binary Numbers

4.1.7Floating Points in Binary

4.1.8Floating Point Arithmetic

4.1.9Bitwise Manipulation

4.1.10Character Sets

4.2Data Structures

4.2.1Arrays, Linked Lists & Queues

4.2.2Graphs, Hash Tables & Stacks

4.2.3Trees

4.3Boolean Algebra

4.3.1Computational Logic

4.3.2Boolean Logic

4.3.3Karnaugh Maps

4.3.4Boolean Identities

4.3.5Flip Flops & Adder Circuits

5Legal, Moral, Cultural & Ethical Issues

5.1Computing Related Legislation

5.1.1Data Protection Act (1998)

5.1.2Computer Misuse Act (1990)

5.1.3Copyright Designs and Patents Act (1988)

5.1.4Regulation of Investigatory Powers Act (2000)

5.2Moral & Ethical Issues

5.2.1Online Activity Tracking

5.2.2Censorship

5.2.3Cultural Issues

5.2.4Environmental Issues

5.2.5Layout, Colour Paradigms & Character Sets

6Elements of Computational Thinking

6.1Thinking Abstractly

6.1.1Abstraction

6.2Thinking Procedurally

6.2.1Decomposition

6.3Thinking Logically

6.3.1Pseudocode & Flow Diagrams

7Problem Solving & Programming

7.1Programming Techniques

7.1.1Programming Fundamentals

7.1.2Modularity

7.2Programming Construction

7.2.1Integrated Development Environments

7.2.2Testing

8Algorithms

8.1Algorithms

8.1.1Interpreting, Correcting & Completing Algorithm

8.1.2Sort Algorithms

8.1.3Insertion & Merge Sort

8.1.4Search Algorithms

Jump to other topics