System Programming Unit III

Programming Language
• Lexical and Syntactic features of a
programming Language are specified by its
grammar
• Language:- collection of valid sentences.
• Sentences: These are the sequence of words.
• Word:- Sequence of letters of graphic symbols.
• The Language specified in this manner is
called as formal Language.

Programming Language Grammar
• A formal Language is a set of rules which
precisely specify the sentence of L.
• Formal Grammar can be represented as :-
• G= {∑ , NT, S, P}
– ∑ set of terminals
– NT set of non terminals
– S Distinguished symbol (Starting symbol)
– P set of productions.

• Terminal Symbol:- These are the symbols
which can not further sub divided
– Ex:- ∑= { a, b,c,d…….0,1,2,3……}
• No terminal symbols:- These are the
combination of terminal symbols which can be
further sub divided.
– Ex:- <A> or <Noun>

• Production :- It is called as re-writing rule
• It can be represented as :-
– Each production consists of a No terminal
followed by an arrow (-) or equal to
(=), followed by string of Non terminals and
terminals
– Ex:- A  b
S  Aa

Syntax Tree

• A Graphical representation of any statement
of a Language is called as syntax tree.

Derivation
• The replacement of Non terminal symbols
according to the given production rule is
called as derivation
• Types of Derivation:
– Leftmost derivation
– Rightmost derivation

Rules for English Language
1) <Sentence>  <NP><VP>
2) <NP>  <article><noun>
3) <VP>  <verb>
4) <VP>  <verb><adverb>
5) <article>  The
6) <noun>  student
7) <verb>  studies
8) <adverb>  hard
9) <adverb>  slowly

Derivation
• Structure Rules applied
• <Sentence>
• <NP><VP> (1)
• <article><noun>< VP> (2)
• <article><noun> <verb><adverb> (4)
• The <noun> <verb><adverb> (5)
• The student <verb> <adverb> (6)
• The student studies <adverb> (7)
• The student studies hard (8)

• Ex. Consider the full grammar,
• E → E+E
• E → E*E
• E → id
• Let us derive the string “ id + id * id”

• Derive the string

–babbaaaba

Required string is

baab

Reduction
• It is the process of replacement of string or
part of string by non terminal according to the
production rule.

• Structure Rules applied
• The student studies hard
• <article> student studies hard (5)
• <article><noun> studies hard (6)
• <article><noun> <verb> hard (7)
• <article><noun> <verb> <adverb> (8)
• <NP> <verb> <adverb> (2)
• <NP><VP> (4)
• <Sentence> (1)

Ambiguity of Grammar
• The Grammar for a language is said to be
ambiguous if there exists at least one string
which can be generated (or, derived) in more
than one way
• i. e. there can be more than one leftmost
derivations, more than one rightmost
derivations & also more than one derivation
trees associated with such a string.

• Complier:-
• These are the system programs which will
automatically translate the High level language
program in to the machine language program

Source program Target program /
High level Lang. Compiler M/C Lang. Prog.
Prog.

Database

• Cross Compiler:-
• These are the system programs which will automatically
translate the HLL program compatible with M/C A, in to the
machine language program compatible with M/C A , but the
underlying M/C is M/C B
Source program Target program /
HLL Prog. Cross Compiler M/C Lang. Prog.
Compatible with
M/C A

M/C B

P Code Compiler
Source
Program

Compiler P-Code interpreter

Obj
Program

Exexute P-Code interpreter

• Very similar in concept of Interpreter
• In pseudo- code complier program is analyzed
and converted into an intermediate form,
which is then executed interpretively.
• The source program is compiled, the resulted
object program is in p-code. This p-code
program is then read and executed under
control of p-code interpreter.

Compilation process overview
• Compilation process is vast and complex.
• Hence it is divided into a series of subtasks
called as phases.
• Each of which transform the source program
form one representation to another.
• The compilation process involves two major
tasks.

Compilation process overview

Analysis of + Synthesis of = Translation
source text Target text of prog in
obj form

• Analysis of source text
– Lexical Analysis (Scanner)
– Syntax Analysis (Parser)
– Semantic analysis.

• Synthesis of target text
– Storage allocation
– Code generation

Analysis of source text

• Determine validity of source statement from
the analysis view point.
• Determine the content of source statement.
• Construct the suitable representation of the
source statement f0r use by the subsequent
analysis phase or by the synthesis phase of
compiler.

Synthesis of target text

• Memory allocation:- It is the simple task given to
the presence of symbol table. The memory
requirement of an identifier is computed from its
length, type and dimension and memory is
allocated to it.
• Code generation:- the code generation uses the
knowledge of target architecture , knowledge of
instruction and also the addressing modes in the
target computer to select the appropriate
instruction.

Synthesis of target text

• The important issues in code generation are
– Determine the space where the intermediate
results should ne kept i.e. whether they should be
kept in memory location or held in machine
register.
– Determine which instruction should be used for
type conversion operation.
– Determine which addressing mode should be
used.

Code Optimization
• This is an optional phase to improve the
intermediate code so that ultimate object
program can run faster and also take less phase.
• The ultimate aim of this technique is to
improve the execution efficiency of a program by
– Eliminating redundancies
– Rearranging the computation in the program with out
affecting target machine.

Code optimization techniques

1. Compile time evaluation
2. Elimination of common sub expressions
3. Frequency reduction
4. Strength reduction
5. Dead code elimination
6. Boolean sub expressions optimization
7. Local and Global optimization.

System Programming Unit III

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System Programming Unit III