CODEWITHSUNDEEP
debuggingassemblysumx86-16dosbox
Anne Blanco
Anne Blanco

Reputation: 3

sum of the squares of the first 5 numbers using DEBUG - Assembly programming in DOSBOX

Please help, I need the sum of the squares of the first 5 numbers using DEBUG - Assembly programming in DOSBOX. This an example of a 2^2:

  -a 100 </i> 
       15BC:0100 mov ax,1 
       15BC:0103 mov bx,2 ; Base Number 
       15BC:0106 mov cx,2 ; Exponent 
       15BC:0109 ;bucle 109: 
       15BC:0109 mov dx,0  
       15BC:010C mul bx 
       15BC:010E loop 109  
       15BC:0110 int 20  
       15BC:0112 
       -g 110

Upvotes: 0

Views: 613

Answers (1)

fcdt
fcdt

Reputation: 2493

The instruction mul bx multiplies the content of ax (always) with the content of the bx register (the parameter). Cause that are 16 bit registers, the result can have up to 32 bits. The lower 16 bits of this result are placed in ax and the higher 16 bits in dx. So you don't have to clear dx before mul. That's only necessary for div.

The code to calculate ax = 3² (in general ax = bxcx) would then be:

    mov  ax, 1
    mov  bx, 3  ; Base Number (that is multiplied by itself cx plus one times)
    mov  cx, 2  ; Exponent (how often the multiplication should be repeated)
expLoop:
    mul  bx
    loop expLoop

If only the square is to be calculated, the loop is no longer necessary and the code could be simplified:

    mov  ax, 3 ; Base Number (that is multiplied by itself one time)
    mul  ax

This will calculate 3² (in general ax²). Note that bx and cx are not used here anymore.

As Michael already mentioned, you have to sum up your results after this if you want to get a sum of squares. Cause cx is not used anymore, it could be used with loop to iterate over all the numbers to be squared. bx could be used to store the sum of the squares:

    xor  bx, bx  ; Sum is initialised to zero
    mov  cx, 5   ; Iterate from 5 down to 1
iterate:
    mov  ax, cx
    mul  cx      ; Calculate the square of the acutal number
    add  bx, ax  ; Sum up the squares in bx
    loop iterate

Upvotes: 2

Related Questions