C89 Compiler and Python Translator

This Compiler/Translator was created from scratch for the coursework section of the second year module Language Processors, which is a part of Electronic and Information Engineering at Imperial College London. The original specification for the project can be found here.

Overview

This program fulfills two functions:

1. Compile programs written in C89 (Also known as C90 or ANSI C) to MIPS Assembly.
2. Translate programs written in a subset of C89 to Python.

Input C files are lexically analysed using Flex and parsed using GNU Bison. The Bison grammar is self written, but does take numerous cues from the original C89 grammar written for use with Yacc (found here).

The Parser generates an Abstract Syntax Tree (AST) of the C program. Each node is represented as a C++ class, with each different construct (e.g. variable, switch case, function declaration) having its own class which inherits from the AST_Node base class. These derived classes each override a pure virtual compilation function (and a Python translation function where required) defined in the base class. By having a parent node call the compilation functions of their children, the tree is traversed and correct assembly/Python code is generated.

How to run the program

Prequisites

• Flex and Bison
• Make
• GCC/G++ (to compile the compiler)

Install

Clone the repository by either downloading the zip file using the Git GUI or using the command line:

git clone https://github.com/adidesh20/C89-Compiler-and-Python-Translator.git

Then, from the top of the directory tree, run:

make bin/c_compiler

Compilation to MIPS

The compilation function is invoked using the flag -S, with the source file and output file specified on the command line:

bin/c_compiler -S [source-file.c] -o [dest-file.s]

Translation to Python

The translator function is invoked using the flag --translate, with the source file and output file specified on the command line:

bin/c_compiler --translate [source-file.c] -o [dest-file.py]

Translator Subset

C to Python translation works for the following C constructs:

Variables

• Local integer variables (though not nested scopes)
• Global integer variables

Functions

• Definition of functions taking 0 or more integer parameters and with void or integer return type
• Explicit support for main special functionality

Statements

• if
• if-else
• while
• return
• sequences

Expressions

• Decimal integer constants
• Integer arithmetic: *,+,-
• Logical operations: &&,||
• Comparison operations: <,==
• Invocation of functions
• Assignment (but only as a direct expression statement)