Computer Systems Lecture 18 Tool Chain and DFAs CS 230 - Spring - PowerPoint PPT Presentation

CS 230 – Introduction to Computers and Computer Systems Lecture 18 – Tool Chain and DFAs CS 230 - Spring 2020 4-1

System Layers Python/C/Racket Code Multiprocessing and Operating Systems Build and Runtime Here now! Environments Memory and Caching CS 230 CPU Instructions and Pipelining Binary Signals & Number Representation Finished! Logic Gates Transistors and Electrical Properties CS 230 - Spring 2020 0-2

Classical Tool Chain  Compiler translates high level language into assembly program.  Assembler translates assembly program into machine code in object file.  Linker combines multiple object files of machine code into program file.  Loader loads program file into main memory.  Library is special object file that can be added to program file during linking or loading. CS 230 - Spring 2020 4-3

Classical Tool Chain Executable or Library Source Code Assembly Code Object File .text beq $2, $0, 1 if a: 0001000000 0001010000 addi $3, $3, 1 b += 1 0010000000 0010000000 .data Compiler Assembler Linker (binasm) Libraries can be created or Loader imported by the linker Main Memory CS 230 - Spring 2020 4-4

Other Execution Approaches  Interpretation  execute source code directly  execute binary code by software  Byte Code  compile to intermediate binary representation  Just-In-Time Compilation  compile during runtime CS 230 - Spring 2020 4-5

Compiler Source Code Assembly Code beq $2, $0, 1 if a: addi $3, $3, 1 b += 1  Program translation  from source language  to target language (usually assembly code)  Typically followed by assembler  to generate machine code CS 230 - Spring 2020 4-6

Basic Compilation Steps  Scanning  also called Lexical Analysis  source code to token sequence  Syntax analysis  token sequence to parse tree  Semantic analysis  use parse tree to generate a symbol table  type check the parse tree against the symbol table  Code generation  parse tree and symbol table to target language CS 230 - Spring 2020 4-7

Scanner / Tokenizer  Also called a “ Tokenizer ”  Convert program text into stream of tokens  Types of tokens (sample):  keyword – 'for', 'while', etc.  operator – '+', '&&', etc.  constant – '1000', '3.5', etc.  delimiter – ':', etc.  variable name – 'minpos', etc.  subroutine name – 'power2', etc. CS 230 - Spring 2020 4-8

Background  Formal languages  Regular languages  Well-studied in theoretical computer science  how to determine if a string is in the language?  deterministic finite automata (DFA)  non-deterministic finite automata (NFA)  regular expressions  Standard algorithms exist CS 230 - Spring 2020 4-9

Deterministic Finite Automata (DFA)  Also known as a deterministic finite state machine (FSM)  Comprised of  A finite set of states  Includes exactly one start state  Includes at least one final (also called accept) state(s)  A finite set of input symbols known as the alphabet  A finite set of transitions from one state to another based on the input  Can determine if input is accepted or rejected CS 230 - Spring 2020 4-10

DFA Example 1 a b  Start state has arrow from nowhere  Final (accept) states are double circles  Notice the start state is also an accept state in this particular DFA  Transitions are marked with the input(s) they consume CS 230 - Spring 2020 4-11

DFA Example 1 a b ab Lets consider the input string:  Begin in the start state CS 230 - Spring 2020 4-12

DFA Example 1 a b ab Lets consider the input string:  Begin in the start state  Place our marker at the start of the string  Look at what transitions (arrows) are available CS 230 - Spring 2020 4-13

DFA Example 1 a b ab Lets consider the input string:  We take the a transition because a is the first character after our marker  Consume the a character and move to the state at the end of the a transition  Look at what transitions are available CS 230 - Spring 2020 4-14

DFA Example 1 a b ab Lets consider the input string:  We take the b transition because b is the first character after our marker  Consume the b character and move to the state at the end of the a transition  Look at what transitions are available CS 230 - Spring 2020 4-15

DFA Example 1 a b ab Lets consider the input string:  Our marker is at the end of the string  No transitions are available  Check if we are in an accept state  We say this DFA accepts the string ab CS 230 - Spring 2020 4-16

DFA Example 2 b d a a c Lets consider the input string: aac CS 230 - Spring 2020 4-17

DFA Example 2 b d a a c Lets consider the input string: aac CS 230 - Spring 2020 4-18

DFA Example 2 b d a a c Lets consider the input string: aac CS 230 - Spring 2020 4-19

DFA Example 2 b d a a c aac Lets consider the input string: We say the DFA accepts the string CS 230 - Spring 2020 4-20

DFA Example 2 b d a a c Now lets consider the input string: abc CS 230 - Spring 2020 4-21

DFA Example 2 b d a a c Now lets consider the input string: abc CS 230 - Spring 2020 4-22

DFA Example 2 b d a a c abc Now lets consider the input string: We’re stuck! We say the DFA rejects the string CS 230 - Spring 2020 4-23

DFA Try it Yourself q d a q m p,l,r amqd Does this DFA accept the string: CS 230 - Spring 2020 4-24

DFA Try it Yourself q d a q m p,l,r amqd Does this DFA accept the string: CS 230 - Spring 2020 4-25

DFA Try it Yourself q d a q m p,l,r amqd Does this DFA accept the string: CS 230 - Spring 2020 4-26

DFA Try it Yourself q d a q m p,l,r amqd Does this DFA accept the string: CS 230 - Spring 2020 4-27

DFA Try it Yourself q d a q m p,l,r amqd Does this DFA accept the string: CS 230 - Spring 2020 4-28

DFA Try it Yourself q d a q m p,l,r amqd Does this DFA accept the string: Yes! DFA accepts the string CS 230 - Spring 2020 4-29

DFA Try it Yourself q d a q m p,l,r amlr Does this DFA accept the string: CS 230 - Spring 2020 4-30

DFA Try it Yourself q d a q m p,l,r amlr Does this DFA accept the string: CS 230 - Spring 2020 4-31

DFA Try it Yourself q d a q m p,l,r amlr Does this DFA accept the string: CS 230 - Spring 2020 4-32

DFA Try it Yourself q d a q m p,l,r amlr Does this DFA accept the string: CS 230 - Spring 2020 4-33

DFA Try it Yourself q d a q m p,l,r amlr Does this DFA accept the string: We’re stuck! The DFA rejects the string CS 230 - Spring 2020 4-34

DFA From Languages  The set of strings accepted by a DFA is called the language accepted by the DFA.  DFAs can be used to detect regular languages  Design DFA to recognize a regular language  used as part of lexical analysis step of compilation  also for input validation  “is this a valid phone number?”  Important DFA restriction: in a given state, there can be at most one choice for a given character CS 230 - Spring 2020 4-35

DFA From Language Example Draw a DFA for the language of all natural numbers. CS 230 - Spring 2020 4-36

DFA From Language Example Draw a DFA for the language of all natural numbers. CS 230 - Spring 2020 4-37

DFA From Language Example Draw a DFA for the language of all natural numbers. 0 CS 230 - Spring 2020 4-38

DFA From Language Example Draw a DFA for the language of all natural numbers. 0 1…9 CS 230 - Spring 2020 4-39

DFA From Language Example Draw a DFA for the language of all natural numbers. 0 1…9 0 …9 CS 230 - Spring 2020 4-40

Try it Yourself Draw a DFA for the language of all combinations of 3 or more lowercase English letters that start with lowercase b. CS 230 - Spring 2020 4-41

Try it Yourself Draw a DFA for the language of all combinations of 3 or more lowercase English letters that start with lowercase b. CS 230 - Spring 2020 4-42

Try it Yourself Draw a DFA for the language of all combinations of 3 or more lowercase English letters that start with lowercase b. b CS 230 - Spring 2020 4-43

Try it Yourself Draw a DFA for the language of all combinations of 3 or more lowercase English letters that start with lowercase b. a…z b CS 230 - Spring 2020 4-44

Try it Yourself Draw a DFA for the language of all combinations of 3 or more lowercase English letters that start with lowercase b. a…z a…z b CS 230 - Spring 2020 4-45

Try it Yourself Draw a DFA for the language of all combinations of 3 or more lowercase English letters that start with lowercase b. a…z a…z b a…z CS 230 - Spring 2020 4-46