The function and purpose of translators

The function and purpose of translators

1. Why use translators?

   • Converts from source code
     • ...to object (machine) code
   • Detect errors in source code

2. Assembly Language

   • What is it?
     • A Low level language/Not portable
     • Uses mnemonics
     • Each instruction translated into one machine code instruction
     • Uses descriptive names (for data stores)
   • Tasks performed
     • Reserves storage for instructions and data
     • Replaces mnemonic opcodes by machine codes
     • Replaces symbolic addresses by numeric addresses
     • Symbol table created to match labels to addresses
     • Checks syntax
   • Machine Code
     • Binary notation
     • Set of all instructions available
       • ...specifically to processor architecture
     • Instructions operate on bytes of data

3. Interpretation & Compilation

   • Interpreter
     • Translates one line
       • ...running the line before translation of next line
     • Errors reported one at a time as checked line by line
   • Compiler
     • Translates whole program together
     • Creates an executable (or intermediate) program
     • Errors may be reported at the same time
     • Optimises code

4. Intermediate Code

   • Partly translated code
     • ...that is portable
       • ...by using an interpreter (virtual machine)
         • (Theoretical computer on which intermediate code can run)
   • Problems
     • Runs slower than executable code
       • (Requires translation upon every run)

5. Lexical Analysis

   • Source code used as input
     • Tokens created from individual symbols in code
       • ...and reserved words
       • Token is a fixed length of binary digits
       • Variable names loaded into symbol table
         • Redundant characters removed
           • Comments removed
             • Error diagnostics given
               • Prepares code for syntax analysis

6. Syntax Analysis

   • Takes output from lexical analysis
     • statements/tokens checked
       • ...against rules of language
       • Errors reported as a list
         • Diagnostics may be given
         • Code is passed to code generation
           • ...further detail added to symbol table

7. Code Generation

   • Code converted into machine code
     • This code is optimised
       • ...increasing effeciency
       • ...reducing number of instructions

8. Library Routines

   • What are they?
     • Pieces of software
       • ...that perform common tasks
   • How do they help?
     • Error-free (tested) code
     • Already written (saves time)
     • Can be used multiple times
     • Programmer can use others' expertise
   • How are they used?
     • Linker used
       • ...to link routine with program
     • Loader used
       • ...to handle addresses
       • ...when program runs