Chapter 5

What is compiler?

A compiler is a special program that processes statements written in a particular

programming language and turns them into machine language or "code" that a

computer's processor uses. Typically, a programmer writes language statements in a language

such as Pascal or C one line at a time using an editor. The file that is created contains what

are called the source statements. The programmer then runs the appropriate language

compiler, specifying the name of the file that contains the source statements. OR

A compiler is a computer program that translates computer code written in one programming

language (the source language) into another language (the target language). The

name compiler is primarily used for programs that translate source code from a high-level

programming language to a lower level language (e.g., assembly language, object code,

or machine code) to create an executable program.

Role of Compiler

Compliers reads the source code, outputs executable code

Translates software written in a higher-level language into instructions that computer

can understand. It converts the text that a programmer writes into a format the CPU

can understand.

The process of compilation is relatively complicated. It spends a lot of time analyzing

and processing the program.

The executable result is some form of machine-specific binary code.

Memory allocation Memory allocation is primarily a computer hardware operation but is managed through

operating system and software applications. Memory allocation process is quite similar in

physical and virtual memory management. Programs and services are assigned with a specific

memory as per their requirements when they are executed. Once the program has finished its

operation or is idle, the memory is released and allocated to another program or merged

within the primary memory.

Memory allocation has two core types;

Static Memory Allocation: The program is allocated memory at compile time.

Dynamic Memory Allocation: The programs are allocated with memory at run time.

Aspects or Phases of a Compilation

The compilation process is a sequence of various phases. Each phase takes input from

its previous stage, has its own representation of source program, and feeds its output to

the next phase of the compiler.

We basically have two phases of compilers, namely Analysis phase and Synthesis phase.

Analysis phase creates an intermediate representation from the given source code.

Synthesis phase creates an equivalent target program from the intermediate

representation.

Symbol Table – It is a data structure being used and maintained by the compiler, consists all

the identifier’s name along with their types. It helps the compiler to function smoothly by

finding the identifiers quickly.

The compiler has two modules namely front end and back end. Front-end constitutes of the

Lexical analyzer, semantic analyzer, syntax analyzer and intermediate code generator. And

the rest are assembled to form the back end.

1. Lexical Analyzer – It reads the program and converts it into tokens. It converts a

stream of lexemes into a stream of tokens. Tokens are defined by regular expressions

which are understood by the lexical analyzer. It also removes white-spaces and

comments.

2. Syntax Analyzer – It is sometimes called as parser. It constructs the parse tree. It takes

all the tokens one by one and uses Context Free Grammar to construct the parse tree.

Why Grammar ?

The rules of programming can be entirely represented in some few productions. Using

these productions we can represent what the program actually is. The input has to be

checked whether it is in the desired format or not.

Syntax error can be detected at this level if the input is not in accordance with the

grammar.

3.Semantic Analyzer – It verifies the parse tree, whether it’s meaningful or not. It

furthermore produces a verified parse tree.It also does type checking, Label checking and

Flow control checking.

4.Intermediate Code Generation- After semantic analysis the compiler generates an

intermediate code of the source code for the target machine. It represents a program for some

abstract machine. It is in between the high-level language and the machine language. This

intermediate code should be generated in such a way that it makes it easier to be translated

into the target machine code.

5.Code Optimization

The next phase does code optimization of the intermediate code. Optimization can be

assumed as something that removes unnecessary code lines, and arranges the sequence of

statements in order to speed up the program execution without wasting resources (CPU,

memory).

6.Target Code Generator – The main purpose of Target Code generator is to write a code

that the machine can understand and also register allocation, instruction selection etc. The

output is dependent on the type of assembler. This is the final stage of compilation.

Code Optimisation

The programs represented in the intermediate code form usually contains much scope for

optimisation both in terms of storage space as well as run time efficiency of the intended

output program. Sometimes the input program itself contains such scope. Besides that, the

process of generating the intermediate code representation usually leaves much room for such

optimisation. Hence, compilers usually implement explicit steps to optimise the intermediate

code.

OR

Optimization is a program transformation technique, which tries to improve the code by

making it consume less resources (i.e. CPU, Memory) and deliver high speed.

In optimization, high-level general programming constructs are replaced by very efficient

low-level programming codes. A code optimizing process must follow the three rules given

below:

The output code must not, in any way, change the meaning of the program.

Optimization should increase the speed of the program and if possible, the program

should demand less number of resources.

Optimization should itself be fast and should not delay the overall compiling process.

Efforts for an optimized code can be made at various levels of compiling the process.

At the beginning, users can change/rearrange the code or use better algorithms to

write the code.

After generating intermediate code, the compiler can modify the intermediate code by

address calculations and improving loops.

While producing the target machine code, the compiler can make use of memory

hierarchy and CPU registers.

Optimization can be categorized broadly into two types : Machine independent and Machine

Dependent.

Machine-independent Optimization

In this optimization, the compiler takes in the intermediate code and transforms a part of the

code that does not involve any CPU registers and/or absolute memory locations.For example

do

{

item = 10;

value = value + item;

} while(value<100);

This code involves repeated assignment of the identifier item, which if we put this way:

Item = 10;

do

{

value = value + item;

} while(value<100);

should not only save the CPU cycles, but can be used on any processor.

Machine-dependent Optimization

Machine-dependent optimization is done after the target code has been generated and when

the code is transformed according to the target machine architecture. It involves CPU

registers and may have absolute memory references rather than relative references. Machine-

dependent optimizers put efforts to take maximum advantage of memory hierarchy.

What Is Interpreter?

In computer science, an interpreter is a computer program that directly executes instructions

written in a programming or scripting language, without requiring them previously to have

been compiled into a machine language program. An interpreter generally uses one of the

following strategies for program execution:

1. Parse the source code and perform its behavior directly;

2. Translate source code into some efficient intermediate representation and immediately

execute this;

3. Explicitly execute stored precompiled code made by a compiler which is part of the

interpreter system.

Role of Interpreter

The interpreter converts the source code line-by-line during RUN Time.

Interpret completely translates a program written in a high-level language into

machine level language.

Interpreter allows evaluation and modification of the program while it is executing.

Relatively less time spent for analyzing and processing the program

Program execution is relatively slow compared to compiler

OR

KEY DIFFERENCE BETWEEN COMPILER AND INTERPRETER

Compiler transforms code written in a high-level programming language into the

machine code, at once, before program runs, whereas an Interpreter coverts each high-

level program statement, one by one, into the machine code, during program run.

Compiled code runs faster while interpreted code runs slower.

Compiler displays all errors after compilation, on the other hand, the Interpreter

displays errors of each line one by one.

Compiler is based on translation linking-loading model, whereas Interpreter is based

on Interpretation Method.

Compiler takes an entire program whereas the Interpreter takes a single line of code.

CHAPTER 6

LINKERS

Linker

• A System Software that Combines two or more separate object programs and supplies the

information needed to allow references between them .

• Two Types/scheme

– Dynamic Linking

– Static Linking

1. Static Linking:

It is performed during the compilation of source program. Linking is performed before

execution in static linking. Static linkers takes input a collection of relocatable object files

and command line arguments and generate as output a fully linked executable object file that

can be loaded and run.

Static linker perform two major task:

Symbol resolution – It associates each symbol reference with exactly one symbol

definition .Every symbol have predefined task.

Relocation – It relocate code and data section and modify symbol references to the

relocated memory location.

2.Dynamic Linking:

Dynamic linking is performed during the run time. This linking is accomplished by placing

the name of a shareable library in the executable image. There is more chances of error and

failure chances. It require less memory space as multiple program can share a single copy of

the library.

Loader

Loader is a part of operating system and is responsible for loading executable files into

memory and execute them. It calculates the size of a program (instructions and data) and

creates memory space for it. It initializes various registers to initiate execution.

There are three kinds of loading approaches/scheme:

1. Absolute loading

2. Relocatable loading

3. Dynamic run-time loading

1.Absolute loading: This approach loads the executable file of a program into a same main

memory location each time. But it has some disadvantages like a programmer must be aware

of the assignment strategy for loading the modules to main memory. In case, the program is

to be modified involving some insertion and deletion in the program, then all the addresses of

the program have to be altered.

2. Relocatable loading: In this approach, the compiler or assembler does not produce actual

main memory address. It produces the relative addresses.

3.Dynamic Run-Time loading: In this approach, the absolute address for a program is

generated when an instruction of an executable module is actually executed. It is very

flexible, the loadable module/executable module can be loaded into any region of main

memory. The executing program can be interrupted in between and can be swapped out to

the disk and back to main memory this time at a different main memory address.

Two more types of loading scheme :-

1] Link-And-Go.

2] Link-Load-And-Go.

1. Link-And-Go

In the Link-And-Go scheme the linkage editor actually situated a program its load address

perform all other linking function and passes control to the purpose of execution.

Drawbacks of the scheme :-

1) Linkage editor co-exist with the program while perform the linkage task.

2) Linking has to be repeated for execution of program.

Fig: Link-and-Go Scheme

2.Link-Load-And Go:-

The Link-Load-And-Go scheme require less storage because its construct a ready to execute

form of a program and push it’s the secondary storage. its necessary to load this program into

the main storage without any relocation. such loader is called as absolute loader.

This loader presents :-

1)Text of program which has been link for desired area.

2)The load address origin.

3)Length of the program.

Fig: Link-Load And Go Scheme

Important Terms:

• Translation time address: Translation time address is used at the translation time. This

address is assigned by translator.

• Linked time address: Link time address is used at the link time. This address is assigned

by linker.

• Load time address: Load time address is used at the load time. This address is assigned by

loader.

• Translated origin: Address of origin assumed by the translator.

• Linked origin: Address of origin assumed by the linker while producing a binary program.

• Load origin: Address of origin assumed by the loader while loading the program for

execution.

Relocation of linking concept.

Program relocation is the process of modifying the addresses used in the address sensitive

instruction of a program such that the program can execute correctly from the designated area

of memory.

• If linked origin≠ translated origin, relocation must be performed by the linker.

• Let AA be the set of absolute address - instruction or data addresses used in the instruction

of a program P.

• AA≠ ф implies that program P assumes its instructions and data to occupy memory words

with specific addresses.

• Such a program – called an address sensitive program – contains one or more of the

following:

-An address sensitive instruction: an instruction which uses an address a∈AA.

-An address constant: a data word which contains an address a∈AA.

• An address sensitive program P can execute correctly only if the start address of the

memory area allocated to it is the same as its translated origin.

• To execute correctly from any other memory area, the address used in each address

sensitive instruction of P must be ‘corrected’.If load origin≠ linked origin, relocation must

be performed by the loader.

Difference Between Linker And Loader

Chapter 7

Software Tools

Software Tools for Program Development

A programming tool or software development tool is a program or application that software

developers use to create, debug, maintain, or otherwise support other programs and

applications. The term usually refers to relatively simple programs that can be combined

together to accomplish a task, much as one might use multiple hand tools to fix a physical

object.

The history of software tools began with the first computers in the early 1950s that used

linkers, loaders, and control programs. Tools became famous with Unix in the early 1970s

with tools like grep, awk and make that were meant to be combined flexibly with pipes. The

term "software tools" came from the book of the same name by Brian Kernighan and P. J.

Plauger.

Software development tools can be roughly divided into the following categories:

1) Performance analysis tools

2) Debugging tools

3) Static analysis and formal verification tools

4) Correctness checking tools

5) Memory usage tools

6) Application build tools

7) Integrated development environment

Given below are few uses of the Software Dev Tools:

Software tools are used to accomplish and investigate the business processes,

document the development process of the software and optimize all the processes.

By using these tools in the software development process, the outcome of the projects

will be more productive.

Using the development tools, a developer can easily maintain the workflow of the

project.

Some of the Best latest Software Development Tools

1)Zoho Creator

It is a low-code platform that enables rapid development and delivery of web and mobile

applications and assists to Build powerful enterprise software applications 10x faster.

It also provides key features like Artificial Intelligence, JavaScript, Cloud functions, third-

party integrations, multi-language support, offline mobile access, integration with a payment

gateway and more.

2) Linx

Linx is low code tool to build and automate backend applications and web services. The tool

accelerates the design, development and automation of custom business processes, including

easy integration of applications, systems and databases.

3) Atom

Atom is an open source and free desktop editor cum source code editor that is up-to-date,

friendly and hackable to the core.

4) Cloud 9

Initially in 2010 Cloud 9 was an open source, cloud-based IDE (Integrated Development

Environment) that supports various programming languages like C, Perl, Python, JavaScript,

PHP etc. Later in 2016, AWS (Amazon Web Service) acquired it for further improvement

and made it chargeable as per the usage.

5) GitHub

GitHub is a powerful collaboration tool and development platform for code review and code

management. With this GitHub, the users can build applications and software, manage the

projects, host the code, review the code etc.

6) NetBeans

NetBeans is an open source and a free software development tool written in Java that

develops world-class web, mobile, and desktop applications easily and quickly. It uses C /

C++, PHP, JavaScript, Java etc.

7) Bootstrap

Bootstrap is an open source and free framework for developing responsive websites and

mobile-first projects using CSS, HTML, and JS. Bootstrap is widely used to design faster and

simpler websites.

8) Node.js

Node.js is an open source, cross-platform and JavaScript run-time environment that is built to

design a variety of web applications and to create web servers and networking tools.

Editors

Editors or text editors are software programs that enable the user to create and edit text files.

In the field of programming, the term editor usually refers to source code editors that include

many special features for writing and editing code. Notepad, Wordpad are some of the

common editors used on Windows OS and vi, emacs, Jed, pico are the editors on UNIX OS.

Features of text editors are — moving the cursor, deleting, replacing, pasting, finding,

finding and replacing, saving etc.

Types of Editors

Therre are generally five types of editors as described below:

1. Line editor: In this, you can only edit one line at a time or an integral number of lines.

You cannot have a free-flowing sequence of characters. It will take care of only one

line.

Ex : Teleprinter, edlin, teco

2. Stream editors: In this type of editors, the file is treated as continuous flow or

sequence of characters instead of line numbers, which means here you can type

paragraphs.

Ex : Sed editor in UNIX

3. Screen editors: In this type of editors, the user is able to see the cursor on the screen

and can make a copy, cut, paste operation easily. It is very easy to use mouse pointer.

Ex : vi, emacs, Notepad

4. Word Processor: Overcoming the limitations of screen editors, it allows one to use

some format to insert images, files, videos, use font, size, style features. It majorly

focuses on Natural language.

5. Structure Editor: Structure editor focuses on programming languages. It provides

features to write and edit source code.

Ex : Netbeans IDE, gEdit.

Overview of the editing process:

• An interactive editor is a computer program that allows a user to create an revise a target

document.

• The document means an object such as computer programs, text,equations tables, diagrams,

photographs etc.

• The document editing process in an interactive user computer dialogue designed to

accomplish four tasks:

1)Select the part of the target document to be viewed & manipulated.

2)Determine how to format this view online and how to display it.

3)Specify and execute operations that modify the target document.

4)Update the view appropriately.

Figure below shows the simple editor :

Fig - Editor Structure

Debug Monitor

Debug Monitor is a powerful graphical- and console-mode tool for monitoring all activities

handled by the Win Driver kernel. we can use this tool to monitor how each command sent to

the kernel is executed.

It will provide details regarding the target system execution and in case of any error this

information will be useful for developers to fix the issue. Some debug monitors records the

error event and reproduce it based on the developer’s need.

The Debug Monitor comes in two versions:

wddebug_gui – a GUI version for Windows 7/Vista/Server 2008/Server

2003/XP/2000 and Linux.

Wddebug – a console-mode version for Windows, Windows CE, and Linux; on

Windows CE, wddebug also supports GUI execution.

Both Debug Monitor versions are provided in the WinDriver/util directory.

1.You can Run the Debug Monitor using either of the following methods:

Run WinDriver/util/wddebug_gui.

Run the Debug Monitor from DriverWizard's Tools menu.

On Windows, run Start | Programs | WinDriver | Debug Monitor.

2.Set the Debug Monitor's status, trace level and debug sections information from the Debug

Options dialogue, which is activated either from the Debug Monitor's View | Debug

Options menu or the Debug Options toolbar button.

Programming Environment

In computer program and software product development, the development environment is the

set of processes and programming tools used to create the program or software product.

The environment is quite literally everything installed on your machine which can affect

either the development and or testing of your application - that can include :

The editors/IDEs you are using (can affect how efficiently you can write code).

Which compilers/interpreters you are using, and their exact versions - can affect

whether your code will execute at all, or how efficiently it does so.

The operating system installed on your machine - Can well have a significant affect

on how your code is written.

The environment variables set on your machine, especially relevant during testing

as these can dramatically affect certain functions of some applications.

The extra libraries installed on your machine (including potentially any installed by

other programs); can effect how well your code will run on other people’s

machines (with potentially different library versions installed)

Other programs running on your machine, especially during load and performance

testing.

The available RAM and Disk space on your machine: can affect how well your

code performs especially under load/stress test conditions

The local network capacity and connectivity: can directly affect how well some

programs function.

User Interfaces (UI)

A user interface, also called a "UI" or simply an "interface," is the means in which a person

controls a software application or hardware device. A good user interface provides a "user-

friendly" experience, allowing the user to interact with the software or hardware in a natural

and intuitive way.

Nearly all software programs have a graphical user interface, or GUI. A typical GUI of a

software program includes a menu bar, toolbar, windows, buttons, and other controls.

Most hardware devices also include a user interface, though it is typically not as complex as

a software interface.

OR

The user interface (UI) is the point of human-computer interaction and communication in a

device. This can include display screens, keyboards, a mouse and the appearance of

a desktop. It is also the way through which a user interacts with an application or a website.

The growing dependence of many businesses on web applications and mobile applicationshas

led many companies to place increased priority on UI in an effort to improve the user's

overall experience.

Types of user interfaces:

The various types of user interfaces include:

graphical user interface (GUI)

command line interface (CLI)

menu-driven user interface

touch user interface

voice user interface (VUI)

form-based user interface

natural language user interface

Examples of user interfaces

Some examples of user interfaces include:

computer mouse

remote control

virtual reality

ATMs

speedometer

the old iPod click wheel