Overview of Language Processor : Fundamentals of LP , Symbol Table , Data Structure for LP

SYSTEM PROGRAMMING
TOPIC : Overview of Language Processor : Fundamentals of LP , Symbol
Table , Data Structure for LP
SUBMITTED BY :
Bhavin Darji
SUBMITTED TO :
Prof.

Fundamentals of Language Processor
Language Processing = Analysis of SP + Synthesis of TP
Source program as a analysis phase
Target program in synthesis phase
There are 3 components
◦ Lexical rule
◦ Syntax rule
◦ Semantic rule

Analysis Phase
This specification consists of three components
Lexical rules
Specify the information and formation of valid lexical units in the source language
Syntax Rules
Specify the information and formation of valid statements in the source language
Semantic Rules
Associated with valid statements of language

Consider the following example
A = (B* 100) /D;
Lexical units identifies =, * and / operators, 100 as constant, and the remaining strings
as identifiers.
Syntax analysis identifies the statement as an assignment statement with A as the left
hand side and (B * 100) / D as the expression on the right hand side.
Semantic analysis determines the meaning of the statement to be the assignment of
B X 100 / D to A.

Synthesis Phase
 It performs two main activities:
 Creation of data structures in the target program (memory allocation)
 Generation of target code (code generation)
 Example
MOVER AREG, PROFIT
MULT AREG, 100
DIV AREG, COST_PRICE MOVEM AREG, PERCENT_PROFIT
…

Lexical Analysis
Reads the source code & divide the source code into tokens.
Token is group of characters with meaning.
Lexical analyzer takes a stream of Lexeme as a input and the output is stream of token.

Example
int a , b;
int Ans;
ans = a+b;
Symbol Type Address
1. int keyword
2. a Identifier 2000

Syntax Analysis
Done in order to verify the grammatical mistake of source code.
Takes a stream of tokens as input and generate a syntax tree.
Example : a=b*c
=
a *
b c

Semantic Analysis
It verify the meaning of each and every sentence.
It just verify weather an operator is operating on required number of operand or not.
Example : int a , b, ans ;
ans = a + b;

Intermediate code generation
Source code is converted into a intermediate representation known as three address code.
Example :
◦ A = b*c+d;
◦ T1=b*c;
◦ A=t1+d;
After this four analysis we get our target program.

The Symbol Table
Advance data structure used by compiler to store complete information of source code at any
phase
If new variable encountered that should be store into the symbol table.
Communicate with each and every phase of compiler.
Lexical
Analyzer
Semantic
Analyzer
Code
Generator
Symbol
Table
Syntax
Analyzer

Criteria of Classification of Data Structure
of LP:
Nature of a Data Structure :
◦ Linear or
◦ Non Linear
Purpose of a Data Structure :
◦ Search or
◦ Allocation

Linear Data Structure
Consist of a linear arrangement of elements in the memory.
Advantage : Facilities Efficient Search
Disadvantage :
◦ Require a contagious area of memory
◦ Wastage of Memory

Non Linear Data Structure
Overcomes the disadvantage of Linear DS.
Elements of Non linear DS are accessed using pointers.
Elements need not occupy contiguous area of memory.

Sequential Search Organization
#1
#2
#f
#n
Occupied Entries
Free Entries
n: Number of entries in the table f: Number of occupied entries

(2)Binary Search Organization
All entries in a table are assumed to satisfy an ordering relation.
‘<‘ relation implies that the symbol occupying an entry is ‘smaller or larger than’ the symbol.
If the new symbol is smaller then it will be put at left side otherwise put at right side.
Every new symbol the existing symbol may have to be shifted to ensure ordering
relation.
Hence , this is not good for the symbol table.
It is suitable for table which has fixed set of symbol.
Ex. Table of reserve word in a programming language.

(3)Hash Table Organization
There are three possibilities when eth entry will be arrived :
- Entry may be occupied by symbol S.
- Entry may be occupied by some other symbol.
- Entry may not occupied.
 Collision: when eth entry will be occupied by some other entry then that is collision.
A simple solution to avoid collision is to enter a distinct entry in symbol table. This technique is
known as direct entry organization.

Allocation Data Structures
1)Stacks
A linear data structure which satisfies following properties:
- Allocation and de-allocation are performed in a LIFO manner.
- Only last element is accessible at any time.
It has a limited size

2)Heaps
Non Linear Data Structure
It is used for dynamic memory
Permits allocation and de-allocation of entities in random order
We are responsible to de-allocate the memory
It has no size restriction
We use pointer to access it , so it is slightly slower.

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