CSCI 3211
Fall 2000
Programming Lab 1
Due 9/12/00

a) Assemble and single step with a debugger the program shown below.
Establish the data window for program variables.  Turn in a listing
and the final debug window resulting from the execution of the program
statements.  The sum variable should show the appropriate value.

b)  Modify this program to meet the following requirements:
The list of words is terminated by a vlue of -1 and the count value is
unknown (uninitialized).  The sum of the list should include all words
up to, but not including, the -1 value.  The count value will have
the number of words accumulated in sum. If overflow occurs after any
addition operation, the byte overflow should be set to 1 and the
program terminated.  See a) above for required lab report. See text for 
conditional branching instructios.

The new data section should appear as follows:
                     list     dw 1,2,3,4,5,-1
                     count    dw 0
                     overflow db 0
                     sum      dw 0

Repeat part a for this new program.

Program listing:
        ;**Program to add words in a list
        .MODEL small
        .STACK 100h
        .DATA
             ;** data section
             list  dw 1,2,3,4,5
             count dw 5  ; you could use  count dw  ($-(offset list))/2
                         ;            or  count equ ($-(offset list))/2
        .CODE
             mov ax,@data      ;standard beginning
             mov ds,ax         ;

                 ;***********  body of program (your code goes here!)
                 mov si,0      ;initialize index for list
                 mov ax,0      ;initialize accumulator for sum
                 mov bx,count

                 Start:        ;a label used for brancing reference
                     dec bx    ;subtract 1 from current contents of bx
                     js Endit  ;conditional goto Endit when bx goes neg
                     add ax,list[si] ;an array style reference to data
                     add si,2  ;index adjusted to reference next word
                     jmp Start ;unconditional goto Start
                 Endit:
                     mov sum,ax ;store accumulated value
                 ;************ program logic ends

             mov ah,04ch        ;standard ending
             int 21h            ;standard ending
        END