Shift and add method for multiplying numbers give garbage output

Question

I have made a procedure that multiplies 2 numbers using add and shift method and stores the result in a buff variable.

Here, buff1 and buff2 are initialised in the data section of the code as word type.

buff1 dw 0AH

buff2 dw 03H

And buff is declared in .bss section as 4 byte.

buff resb 4

Here is the procedure that does the multiplication :

shift_add:
    movzx eax,word[buff1]     ;2byte
    movzx ebx,word[buff2]
    mov edx,0H
    mov rcx,16  ;integer
    backs:
        shr bl,1
        jnc haha
        add edx,eax
    haha:
        shl eax,1
    loop backs  
    mov dword[buff],edx
    print buff,4
ret

Why is the above code giving me garbage output ?enter image description here

Because you forgot to convert to text for printing. Note it printed the character 0x1e which is in fact the correct answer. — Jester
– Jester, Commented Mar 30, 2018 at 18:05
Because you didn't convert it to text. If you look at an ascii table you will see it's unprintable character, and the terminal is trying its best to display it. — Jester
– Jester, Commented Mar 30, 2018 at 18:12
Many a times when I print it like that, then it works but not now !! Also 001E will be of 2 bytes but I have passed 4 as 2nd argument with buff as 1st argument in the print buff,4 instruction. Why are other 0s not getting printed ? — asn
– asn, Commented Mar 30, 2018 at 18:16
Presumably your terminal simply ignores zero bytes. It is printed though. You can see it if you pipe it into a hex dump for example. print only works if you provide it text. Your "many a times" probably involved text not binary. — Jester
– Jester, Commented Mar 30, 2018 at 18:25

toncsi · Accepted Answer · 2018-05-16 22:10:10Z

1

try shr ebx,1 instead of shr bl,1.

answered May 16, 2018 at 22:10

toncsi

3135 silver badges8 bronze badges

Sign up to request clarification or add additional context in comments.

Collectives™ on Stack Overflow

Shift and add method for multiplying numbers give garbage output

1 Answer 1

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

Comments

Your Answer

Sign up or log in

Post as a guest

Related