Compiler design
- 1. NADAR SARASWATHI COLLEGE OF ARTS&SCIENCE,THENI DEPARTMENT OF COMPUTER SCIENCE&INFORMATION TECHNOLOGY V.S.PRIYADHARSHINI I-MSC(CS)
- 2. COMPILER DESIGN TOPIC: DATA STRUCTURES FOR SYMBOL TABLES
- 3. DATA STRUCTURES FOR SYMBOL TABLES Symbol Table in Compiler A symbol table is a data structure employed by a language translator, like a compiler or interpreter, within which each identifier in a program's source code is connected with information about its declaration or presence in the source code, like its type, scope level, and infrequently its position. A symbol table is a significant data structure used in a compiler that correlates characteristics with program identifiers. The analysis and synthesis stages employ symbol table information to verify that used identifiers have been specified, to validate that expressions and assignments are semantically accurate, and to build intermediate or target code.
- 4. There are three data structures used to implement symbol table: Linear List Binary Search Tree Hash Table
- 5. LINEAR LISTS Linear Lists It is the simplest and most straightforward method of implementing data structures. To store names and their accompanying information, we use a single array. New names are added to the list in the order that they appear. To add a new name, we must first check the list to ensure that it does not already exist.
- 7. TREES Trees It is a more efficient method of organizing symbol tables. Each record now has two link fields, LEFT and RIGHT. The procedure below is used to find NAME in a binary search tree where x is originally a reference to the root.
- 8. 1. while x ≠ null do 2. if NAME = NAME(x) then /* NAME found take action on success*/ 3. else if NAME < NAME(x) then x:=LEFT(x) /* visit left child*/ 5. else /* NAME (p)<NAME*/ X:= RIGHT(x) /*visit right child*/
- 9. HASH TABLE Hash Table Hashing table technique is suitable for searching and hence it is implemented in compiler.
- 11. HASH FUNCTION Hash Function The hash function is the mapping between an item and the place in the hash table where that item resides. The hash function takes a collection item and returns an integer in the range of slot names from 0 to m-1.
- 12. Example: Assume that we have the set of integer items 59, 28, 93, 18, 77 and 31. Consider m=11 (number of slots of hash table) Suppose we want to insert the above elements within the slots by using formula: h(item) % m 59 % 11 = 4 28 % 11 = 6 93 % 11 = 5 18 % 11 = 7 77 % 11 = 0 31 % 11 = 9