CS 210

PROJECT #2                                    Due: Noon Tuesday 03/03/05

     This project acquaints the student with issues involved in creating
an "interactive" program in assembly language for the Linux environment.

                           PROBLEM STATEMENT

     Design an assembly language program that will assist programmers in
choosing valid symbol-names to use as statement-labels in their assembly 
language programs.  Here is the definition of a symbol-name, quoted from 
the official GNU assembler manual (online):    

         A symbol is one or more characters chosen from the set of all 
  letters (both upper and lower case), digits and the three characters 
  `_.$' (i.e., underscore, period, and currency-sign).  No symbol may 
  begin with a digit.  Case is significant.  There is no length limit: 
  all characters are significant.  Symbols are delimited by characters 
  not in that set, or by the beginning of a file.  (Note that because 
  the source program must end with a newline, the end of a file is not 
  a possible symbol delimiter).
 
Your program should be constructed as an endless loop, which asks a user
to type in a proposed symbol-name, then reports whether or not the reply
that the user enters obeys the above rules for a valid symbol-name.  The
program-loop should terminate in case the user enters an empty character
string (i.e., just a newline character).  This is what a sample terminal
sesion would look like:  

	$ project2

	Please type a proposed symbol-name on the line below: 
	xyz$123
	Yes, you typed a valid assembly language symbol-name.

	Please type a proposed symbol-name on the line below: 
	123_xyz
	No, you typed an invalid assembly language symbol-name.

	Please type a proposed symbol-name on the line below: 
	
	$	

                              REQUIREMENTS

     Your program should be written entirely in assembly language and be
contained in just one source-file (named 'project2.s').  To assemble and
link your program, you should use this command-sequence:

		$ as project2.s -o project2.o
		$ ld project2.o -o project2

You will need to make use of three Linux kernel system-calls (for write,
read, and exit), as illustrated in several prior program demos.  Turn in
a printed copy of your program source-file plus a one-page printout that
shows a sample terminal-session, and put all three of your program files 
('project2.s', project2.o', and 'project2') into your '/submit' folder.
________________________________________________________________________
Allan B. Cruse          University of San Francisco          Spring 2005