Lab 4
 
Part 1

Modify sim5.c to accept zero to three command line arguments.

   1. The first command line argument (e.g. sim5 100 < code.sim5) overrides the value
      of MAXCNT.
   2. The second command line argument (e.g. sim5 100 50 < code.sim5) overrides MAXCNT
      and delays printing the trace output until the 50th instruction is executed.
   3. The third command line argument (e.g. sim5 100 50 75) overrides MAXCNT and only
      traces the 50th to the 75th instruction executed.

Your sim5.c program comments might appear as follows:

/* sim5.c   add push, pop, call, ret to sim4                                */
/* Last modified on September 13, 2012                                      */
/* usage "sim5 < test.sim5" up to 100 cycles with trace                     */
/* usage "sim5 1000 < test.sim5" up to 1000 cycles with trace               */
/* usage "sim5 1000 800 900 < test.sim5" up to 1000 cycles trace 800 to 900 */
/* usage "sim5 1000 0 0 < test.sim5" up to 1000 cycles with no trace        */
 
You should print error messages for illegal command line arguments such as

     sim5 test.sim5
	 sim5 a b c < test.sim5  
	 sim5 100 200 300 < test.sim5
	 sim5 500 300 200 < test.sim5
	 

Part 2

   The following main program reads two integers and prints their product using 
   function mult() to perform the multiplication. 
   
   main:   in    %r1
           in    %r2
           lda   mult
           call  %r0		   
           out   %r0
           halt
   mult:   clr   %r0
   loop:   skeq  %r1
           ret
		   addr  %r2,%r0
		   dec   %r1
		   jmp   loop
           
1. The following main program reads a single integer (n) and prints factorial n. Write 
   function %r0=fact(%r1) to complete the program. Your fact() function must call 
   function %r0=mult(%r1,%r2) to do the multiplication.

   main:   in    %r1
           ldi   fact
           call  %r0		   
           out   %r0
           halt
   fact:   ...
           ...
   mult:   ...
           ...

2. Rewrite problem (1) making function %r0=fact(%r1) a recursive function. (Function
   fact() must still call mult() to perform the multiplication). Note that anything
   in in registers %r0 to %r9 before fact() calls itself is likely to disappear before
   the return (the called version of fact will use the same registers. Use the stack
   (push and pop) to store any needed register values.