# HG changeset patch
# User Christian Urban <christian dot urban at kcl dot ac dot uk>
# Date 1385643061 0
# Node ID 33175abd54742635e4f069eee4049c4a37880d3b
# Parent  ad9b08267fa4cd20307e41a270fe9ad785faadb2
added

diff -r ad9b08267fa4 -r 33175abd5474 coursework/cw03.pdf
Binary file coursework/cw03.pdf has changed
diff -r ad9b08267fa4 -r 33175abd5474 coursework/cw03.tex
--- a/coursework/cw03.tex	Wed Nov 27 21:36:52 2013 +0000
+++ b/coursework/cw03.tex	Thu Nov 28 12:51:01 2013 +0000
@@ -95,7 +95,7 @@
 \end{center}
 
 \noindent
-in order to translate it to Java Byte Code. The resulting class file can be
+in order to translate it to Java byte code. The resulting class file can be
 run with
 
 \begin{center}
@@ -133,7 +133,7 @@
 \noindent
 The intended meaning is to first assign the variable \textit{Id} the value of the first arithmetic 
 expression, then go through the loop, at the end increase the value of the variable by 1, 
-and finally test wether the value is not less or equal anymore to the value of the second
+and finally test wether the value is not less or equal to the value of the second
 arithmetic expression. For example the following instance of a \texttt{for}-loop 
 is supposed to print out the numbers \texttt{2}, \texttt{3}, \texttt{4}.
 
@@ -191,9 +191,9 @@
 (therefore
 you need to download the additional package Jasmin---see above). But it does contain a 
 disassembler, called \texttt{javap}. A dissembler does the ``opposite'' of an assembler: it
-generates readable assembler code from Java Byte Code. Have a look at the
-following example. Compile using the usual Java compiler, 
-\texttt{java}, the simple Hello World program below:
+generates readable assembler code from Java byte code. Have a look at the
+following example. Compile using the usual Java compiler, the simple Hello World 
+program below:
 
 \begin{center}
 \begin{minipage}{10cm}
@@ -215,9 +215,9 @@
 \end{center}
 
 \noindent
-in order to see which Java Byte Code has been generated for this
+in order to see the assembler instructions of the Java byte code that has been generated for this
 program. You can compare this with the code generated for the Scala
-version of Hello Worlds.
+version of Hello World.
 
 \begin{center}
 \begin{minipage}{10cm}
@@ -231,6 +231,81 @@
 \end{minipage}
 \end{center}
 
+\subsection*{Library Functions}
+
+You need to generate code for the instruction \texttt{write} and \texttt{read}. This
+will require to add some ``library'' functions to your generated code. The first
+command even needs two versions, because you might want to write out an
+integer or a string. The Java byte code will need two separate functions for this.
+For writing out an integer, you can use the code
+
+\begin{center}
+\begin{minipage}{12cm}
+\begin{lstlisting}[basicstyle=\ttfamily, numbers=none]
+.method public static write(I)V 
+    .limit locals 5 
+    .limit stack 5 
+    iload 0 
+    getstatic java/lang/System/out Ljava/io/PrintStream; 
+    swap 
+    invokevirtual java/io/PrintStream/println(I)V 
+    return 
+.end method
+\end{lstlisting}
+\end{minipage}
+\end{center}
+
+\noindent 
+This function will invoke Java's \texttt{println} function for integers. Then if you need
+to generate code for \texttt{write x} where \texttt{x} is an integer variable, you can generate
+
+\begin{center}
+\begin{minipage}{8cm}
+\begin{lstlisting}[basicstyle=\ttfamily, numbers=none]
+iload n 
+invokestatic XXX/XXX/write(I)V
+\end{lstlisting}
+\end{minipage}
+\end{center}
+
+\noindent
+where \texttt{n} is the index where the value of the variable \texttt{x} is
+stored. The \texttt{XXX/XXX} needs to be replaced with the class name 
+which you use to generate the code (for example \texttt{fib/fib} in case
+of the Fibonacci numbers).
+
+Writing out a string is similar. The corresponding library function is
+
+\begin{center}
+\begin{minipage}{12cm}
+\begin{lstlisting}[basicstyle=\ttfamily, numbers=none]
+.method public static writes(Ljava/lang/String;)V
+   .limit stack 2
+   .limit locals 2
+   getstatic java/lang/System/out Ljava/io/PrintStream;
+   aload 0
+   invokevirtual java/io/PrintStream/println(Ljava/lang/String;)V
+   return
+.end method
+\end{lstlisting}
+\end{minipage}
+\end{center}
+
+\noindent
+and the code that needs to be generated for \texttt{write "some\_string"} commands 
+is
+
+\begin{center}
+\begin{minipage}{8cm}
+\begin{lstlisting}[basicstyle=\ttfamily, numbers=none]
+ldc "some_string"
+invokestatic XXX/XXX/writes(Ljava/lang/String;)V
+\end{lstlisting}
+\end{minipage}
+\end{center}
+
+\noindent
+Again you need to adjust the \texttt{XXX/XXX} part in each call.
 
 \end{document}