2.2 Sum by DoubleWord

;Write a program in Assembly that adds the following numbers represented in a vector of byte: -5,-45,-96,-128
;Sum must be saved into variable 'risultato' of type doubleword
;Sum again at 'risultato' the addend value, variable of type doubleword with value 69000
;-When debugging, be careful to way in which doubleword are stored

;IMPLEMENTATION
;Variables of vector are byte in CA2
;-To execute the sum on word, it's need of extend the sign: CBW (NB: ONLY for CA2)
;Doubleword variables are stored starting from the least significant byte
;Partial result on word must be extended to doubleword: CWD (NB: ONLY for CA2)
;Attention to the sum of carry when it is necessary:
;ADC instruction

.MODEL small
.STACK
.DATA
vett DB 5,-45,-96,-128
RES DD ?
ADDENDO DD 69000
.CODE
.START
MOV CX,4
MOV BX,0
MOV DX,0
ciclo: MOV AL,vett[BX] ;In ciclo I save sum of elements
       INC BX
       CBW
       ADD DX,AX ;I use DX like temporary container so that I don't use other variables
       DEC CX
       JNZ ciclo
MOV AX,DX
CWD
ADD AX,WORD PTR ADDENDO
ADC DX,WORD PTR ADDENDO+2 ;When I must sum at DX, I do always ADC
MOV WORD PTR RES,AX
MOV WORD PTR RES+2,DX ;So, when I have a number in 32 bit
                      ;in which I must pass a number in 32 bit
                      ;I divide my number into two registers
                      ;AX e DX, and then I copy into RES like I did
                      ;here!!!! DOUBLE WORD ARE TREATED SO!

.EXIT
END