\chapter{Top Algorithm of the Two C Programs}
\section{Algorithm of the Original C Program}
\dspaceoff
\begin{verbatim}
   Begin
      read in file and store in the oggin memory
      initialise the main components of the cpu
      set endofprogram to false

      LOOP for each instruction cycle
           read cycle to get an instruction value
           decode and decide the opcode group
           switch opcode group
                  case group 1 : do group 1
                                    further decode opcode of group 1
                                    execute the opcode instruction
                  case group 2 : do group 2
                                    further decode opcode of group 2
                                    execute the opcode instruction
                  case group 3 : do group 3
                                    further decode opcode of group 3
                                    execute the opcode instruction
           output the one-line results and the stack (if any) and update pc
      UNTIL endofprogram is true

   End. 
\end{verbatim}
\newpage
\section{Algorithm of the Revised C Program}
\begin{verbatim}
    Begin
       make sure only one input data file supplied
       show title of the machine
       show introduction messages and instructions
       show one line of registers names
       read in file and store in the newogg memory
       create 15 windows and 1 pad
       initialise the main components of the cpu
       loop for each instruction cycle
    End
\end{verbatim}
\subsection{Algorithm of the Instruction Cycle}
\begin{verbatim}
    Begin
       set endofprogram to false
       
       LOOP for each instruction cycle
            if pc not equal to 0
               show the previous assembly language mnemonics in assl_win
            read cycle to get an instruction value
            decode and decide the opcode group
            move the basic information of the instruction to expl_win
            save the previous opcode group
            switch opcode group
                   case group 1 : decode and execute group 1 opcode,and
                                  display results.
                   case group 2 : decode and execute group 2 opcode,and
                                  display results.
                   case group 3 : decode and execute group 3 opcode,and
                                  display results.
            lookahead (decode next instruction without executing it and move
                            its assembly language form below the current one)
            refresh all the window to show the screen display
            read in a character (ch)
            if (ch is q)  stop the program
            clear the windows and turn off the highlight functions for
                                                next instruction cycle
            save value of acc
       UNTIL endofprogram is true

    End
\end{verbatim}
The source of the main procedures for decoding and executing the opcodes
are held in files newg1.c, newg2.c and newg3.c for groups 1, 2 and 3
respectively.