\documentclass[a4paper]{article}
\usepackage[portuges]{babel}
\usepackage{a4wide}
\usepackage[latin1]{inputenc}
\usepackage{epsf}

\parindent=0pt
\parskip=2pt
\newtheorem{questao}{Quest\~{a}o}

\def\site{\emph{site}}
\def\internet{\textsf{Internet}}
\def\sgml{\textsf{SGML}}
\def\html{\textsf{HTML}}
\def\dtd{\textsf{DTD}}
\def\w3{\textsf{WWW}}
\def\vm{\textsf{VM}}

\title{Generating Code for the Virtual Machine \vm\\ A small example}
\author{Daniela Carneiro da Cruz \and Pedro Rangel Henriques}
\date{\{danieladacruz,prh\}@@di.uminho.pt\\ Departamento de Inform\'{a}tica, CCTC\\ Universidade do Minho}
\begin{document}
\maketitle


The purpose of this document is twofold.
On one hand we want to present an example of a \vm\ program in its assembly language; 
that program shows how to use a subset of assembly instructions, and illustrates their operational semantics.\\
On the other hand we intend to illustrate a translation scheme from a high-level
programming language to assembly code.

%--------------------------------------------------------------------------
\section{A LISS Source Program}
Suppose we have the following program, written in the high-level programming language 
\textsf{LISS} (\textbf{L}anguage of \textsf{I}ntegers, \textsf{S}equences and \textsf{S}ets),
and we want to execute it.\\
For that it is necessary to translate that program into the code (assembly or binary) of a target machine.


@o Integers.liss
@{
program IntegerTest {

Declarations

    intA := 4, intB, intC := 6 -> integer;
    c := [1,2,3], vector -> Array size 8;
    flag := false -> boolean;


Statements

    intA = -3 + intC * (7 + c[1]); 
    writeLn(c);
    c[5] = 1; 

/* logic operations */

    bool = !( (intA == intB) || (intA != intC) && (c[1] < 6) ) || flag;
}
@}

\section{Generated VM Code}

To run the program above in the \vm\ virtual machine, it should be translated to \vm\ assembly code, 
either manual or automatically.\\
Bellow, we list the code generated by our \textsf{LissCompiler}.

@o Integers.vm
@{
// Line 6: intA := 4, intB, intC := 6 -> Integer
PUSHI 4

PUSHI 0

PUSHI 6

// Line 7: c := [1,2,3], vector -> Array size 8
PUSHI 1
PUSHI 2
PUSHI 3
PUSHI 0
PUSHI 0
PUSHI 0
PUSHI 0
PUSHI 0

PUSHI 0
PUSHI 0
PUSHI 0
PUSHI 0
PUSHI 0
PUSHI 0
PUSHI 0
PUSHI 0

// Line 8: flag := false -> Boolean
PUSHI 0

START

// Line 13: intA = -3 + intC * (7 + c[1])
PUSHI -3
PUSHG 2
PUSHI 7
PUSHGP
PUSHI 3
PADD
PUSHI 1
PUSHI 1
MUL
DUP 1
CHECK 0,7
LOADN
ADD
MUL
ADD
STOREG 0
@}

@o Integers.vm
@{

// Line 14: writeLn(c)
PUSHS "]"
PUSHG 10
STRI
PUSHS ","
PUSHG 9
STRI
PUSHS ","
PUSHG 8
STRI
PUSHS ","
PUSHG 7
STRI
PUSHS ","
PUSHG 6
STRI
PUSHS ","
PUSHG 5
STRI
PUSHS ","
PUSHG 4
STRI
PUSHS ","
PUSHG 3
STRI
PUSHS "["
CONCAT
CONCAT
CONCAT
CONCAT
CONCAT
CONCAT
CONCAT
CONCAT
CONCAT
CONCAT
CONCAT
CONCAT
CONCAT
CONCAT
CONCAT
CONCAT
WRITES
@}

@o Integers.vm
@{

// Line 15: c[5] = 1
PUSHGP
PUSHI 3
PADD
PUSHI 5
PUSHI 1
MUL
DUP 1
CHECK 0,7
PUSHI 1
STOREN

// Line 19: bool = !((intA == intB) || (intA != intC) && (c[1] < 6)) || flag
PUSHG 0
PUSHG 1
EQUAL
PUSHG 0
PUSHG 2
EQUAL
NOT
PUSHGP
PUSHI 3
PADD
PUSHI 1
PUSHI 1
MUL
DUP 1
CHECK 0,7
LOADN
PUSHI 6
INF
AND
OR
NOT
PUSHG 20
OR
STOREG 19

STOP

@}

\section{Files in document}
@f

            
\end{document}