1.5 Generate reverse vector without support vector

;Given a vector of DIM word in memory, replace it with reverse vector (without using another vector support)

;BEFORE                AFTER
;423                   9
;3191                  3
;23                    -412
;11                    11
;-412                  23
;3                     3191
;9                     423

;1° SOLUTION:

DIM EQU 7
.MODEL small
.STACK
.DATA
vett DW 423, 3191, 23, 11, -412, 3, 9
.CODE
.STARTUP
MOV CX, DIM/2 ;I write so because I will use XCHG instruction that exchanges the values of two operands, then it will cycle DIM/2 times
XOR SI,SI
MOV DI,(DIM-1)*2 ;DI takes the value of index of last element, in fact vett is DW, so, first to all, I do
                 ;DIM-1 because vector's index starts from 0, and then I multiply for 2 because, being DW,
                 ;I slide vector's cells two by two, because DW's dimension is 16 bit
ciclo: MOV AX,vett[SI]
       XCHG vett[DI],AX ;By XCHG I exchange values of two operands
       MOV vett[SI],AX
       ADD SI,2
       SUB DI,2
       DEC CX
       CMP CX,0
       JNZ ciclo
.EXIT
END


;2° SOLUTION:

DIM EQU 7
.MODEL small
.STACK
.DATA
vett DW 423, 3191, 23, 11, -412, 3, 9
.CODE
.STARTUP
MOV CX,DIM
XOR SI,SI ;I initialize SI to 0

ciclo1: PUSH vett[SI] ;PUSH takes value of vett[SI]
                      ;and places it into stack memory, on top
        ADD SI,2
        DEC CX
        CMP CX,0
        JNZ ciclo1

MOV CX,DIM
XOR SI,SI

ciclo2: POP vett[SI] ;POP takes values that I placed into stack memory
                     ;and places them into vett[SI]
        ADD SI,2
        DEC CX
        CMP CX,0
        JNZ ciclo2

.EXIT
END