Question

Write LEGv8 "shift assembly instruction" to achieve the multiplication of a binary number by 16

Answer 1

Solution:

to_binary    PROC
  push   BX ; save registers
push   CX
push    DX
xor AX,AX    ; result := 0
mov    CX,4    ; max. number of octal digits
repeat1:
; loop itarates a maximum of 3 times;
; but a NULL can terminates it early
mov    DL,[BX]      ; read the octal digit
cmp    DL,0 ; is it NULL?
je    finished ; if so, terminate loop
and    DL,0FH ; else, convert char. to numeric
shl AL,4 ; multiply by 16 and add to binary
add    AL,DL
inc BX ; move to next octal digit
loop    repeat1 ; and repeat
finished:
pop    DX ; restore registers
pop    CX
pop    BX
ret
to_binary    ENDP
END    main