Lecture by: Prof. Pooja Vaishnav

Language Processor implementations are highly influenced by the kind of storage structure used for program variables and data.

Managing Language requires allocating and managing the memory used by the program in static or dynamic environments.

Implementation of suitable data structure becomes critical in designing and executing the system programs.

The Program behavior depends on the search and allocation structures, the language support and their features such as external reference, recursion etc.

Vital operations: Search and Allocation

Choice of Data Structure: The design of runtime and storage

management system is greatly influenced by the nature of source language.

The structure and composition of source language commands the requirements of the language processor, takes up the job of code generation and allocates memory for the program objects that have their own logical address space

Choice of Data Structure: Nature of Data Structure▪ Linear or non linear▪ Linear data structure involves linear data

elements arrangements▪ Search efficiency is considered by requirement

of contiguous memory allocations for the elements

▪ Sometimes designer may compelled to overestimate the memory requirements of the linear data structure in order to ensure that later on memory requirements would not expand.

▪ This often leads to wastage of memory.▪ Easy Access▪ Implemented as Arrays or Linked Lists

Choice of Data Structure: Nonlinear data structure are the alternatives Uses pointer implementations to access

elements Need not occupy contiguous memory

locations More flexible in allocation and availability of

space Lower search efficiency Interleaved memory locations

Choice of Data Structure: Purpose of Data Structure▪ Whether Search data structure or

Allocation Data Structure▪ Search Data Structure: ▪ Provides efficient search▪ Maintain attribute information ▪ Include table and sequential organization,

binary search organization, hash tables, linked lists, tree structure

Choice of Data Structure: Purpose of Data Structure▪ Whether Search data structure or

Allocation Data Structure▪ Allocation Data Structure:▪ Include stack and heap organizations▪Not required the search operation and address of the memory

Language Processors uses both, search and allocation data structure.

Choice of Data Structure: Lifetime of Data Structure▪ Whether it is used during language

process or the target program execution ▪ For ex., a data structure used during a

language process would have the scope till that process only.

Also called as search structure Designed and used for its search

efficiency during language processing Set of entries, with each

encompassing the information concerning one entity

Maintains attribute information about different entities defined and used in the source program

Entry will be done only once but can be searched many times

Primarily created to store table of information

Mainly created and used during analysis phase of program

Target program rarely use this data structure

Used for Symbol Table implementation

Characterized by ‘key’, special symbol field containing name of entity to assist search operation

Entry: set of fields referred to as record Entry contains two parts: Value in fixed part determines the

information to be stored in the variable part Fixed (tag): Symbol, class type, length,

dimension information, number of parameters, their addresses, type of returned value, length of returned value, statement number

Variable : name, class, statement number

Fixed length entry enable use of homogeneous linear data structures

eg. Arrays, they may contain records having identical format

Suffers from inefficient use of memory usage

Variable length entry leads to compact organization with no memory wastage

Fixed length Entry

Variable length entry

More access efficiency

Less access efficiency

Less memory efficiency

More memory efficiency

Combining the functionality of two: Hybrid Entry Format:

Fixed Part Pointer

Length Variable Part

Kind of data structure, which is used in language processing as both, search and allocation data structures

Fixed (Tag ) Part

Variant Part

Procedure Address of Parameter List,Count of Parameters

Variable Type, Length, Dimension Information

Label Statement Number

Function Length of returned value, type of returned value, number of parentheses and their addresses

InsertSearchDelete

1. Predict entry ‘e’ in the search data structure at which symbol symb is stored

2. Let symbe be the symbol found at eth

entry . Compare symbe with symb.

a. If a match between the two is found, exit with success.

b. Else go to the next step.3. Repeat steps 1 and 2 till all entries are

evaluated or concluded that the symbol does not exist in the search data structure

Table OrganizationSequential Search Organization

Table OrganizationSequential Search Organization

Occupied entries Free Entries Physical Deletion Logical Active/ Deleted Records

Binary Search Organization Search based on relational operators Entry number must not change after adding

record Hash Table Organization

Hash function is used for the mapping of a key value and the slot where that value belongs to the hash table

Hash function takes any key value from the collection and computes on the integer value from it in the range of slot names, between 0 and m-1.