ALP to multipy numbersWITHOUT MUL instruction

Q: Write a ALP to multiply two 8 bit numbers using Shift-Add Method and Repeated Addition Method. Accept the numbers from the user. Make the program a menu driven one.

 

 Code:

Assembler:-NASM
OS:- Linux-64 bit(Fedora)

;Author:-Abhishek Munagekar
;Expno:- 6
;Title:- Multiplication of 8 bit values
;macros begins
%macro read 2
mov rax,00h
mov rdi,01h
mov rsi,%1
mov rdx,%2
syscall
%endmacro
%macro write 2
mov rax,01h
mov rdi,00h
mov rsi,%1
mov rdx,%2
syscall
%endmacro
;macros end
section .data
msg1:  db 10,"=========================================",10
 db "                MENU                     ",10
 db "=========================================",10
 db "1.Successive Addition",10
 db "2.Shift and Add Method",10
 db "3.Exit",10
len1: equ $-msg1
msg2: db "Enter the value for the first number multiplicand",10
len2: equ $-msg2
msg3: db "Enter the value for the second number multiplier",10
len3: equ $-msg3  

section .bss
count resb 1
choice resb 2
amultiplier resb 3 ;ascii
amultiplicand resb 3 ;ascii
multiplier resb 1 ;hex
multiplicand resb 2 ;hex,extra for shifting
answer resb 2  ;hex
aanswer resb 4  ;ascii
section .text
global _start:
_start:
write msg1,len1

read choice,2
cmp byte[choice],31h
je sucadd
cmp byte[choice],32h
je shadd
cmp byte[choice],33h
je exiter
jmp _start    ;jump to start if invalid choice

sucadd:     ;code for successive addtion here
write msg2,len2
read amultiplicand,3
mov r8,amultiplicand
mov r9,multiplicand
mov byte[count],2
call a2h


write msg3,len3
read amultiplier,3
mov r8,amultiplier
mov r9,multiplier
mov byte[count],2
call a2h


    ;now we have hex value in place
mov word[answer],0h
movsx r10,byte[multiplicand]
loop2:
add word[answer],r10w
dec byte[multiplier]
jnz loop2
                  ;now we have the answer at the memory location answer
call h2a
write aanswer,4

jmp _start
;======================================================
shadd:    ;code for shift and add here
write msg2,len2
read amultiplicand,3
mov r8,amultiplicand
mov r9,multiplicand
mov byte[count],2
call a2h


write msg3,len3
read amultiplier,3
mov r8,amultiplier
mov r9,multiplier
mov byte[count],2
call a2h
    ;now we have the hex values in place
mov byte[count],8
mov word[answer],0h
movsx ax,byte[multiplier]
mov bx,word[multiplicand]
mov cx,0   ;cx will store the sum of the partial products
shaddloop:
rcr ax,01
jnc nocarry
add cx,bx   ;add if carry
nocarry:
shl bx,01
dec byte[count]
jnz shaddloop
mov word[answer],cx ;answer obtained
call h2a
write aanswer,4
jmp _start


exiter:
mov rax,60 ;exit system call 
mov rdx,01h
syscall

a2h:   ;ascii to hex r8 source ,r9 destination, counter at count
mov bl,0h
loop:
rol bl,4
mov al,byte[r8]
sub al,30h
cmp al,9h
jbe nocorrection
sub al,7h
nocorrection:
add bl,al
inc r8
dec byte[count]
jnz loop
mov byte[r9],bl
ret

h2a:   ;r9 destination,counter is set to 4,source is set to answer
mov r9,aanswer
mov byte[count],4
mov bx,word[answer]
loop3:
rol bx,04
mov al,bl
and al,0Fh
cmp al,9
jbe def
add al,7h
def:
add al,30h
mov byte[r9],al
inc r9
dec byte[count]
jnz loop3 
ret
;========================================

Output

[secomp@localhost as6]$ nasm -f elf64 as6.asm
[secomp@localhost as6]$ ld -o as6 as6.o
[secomp@localhost as6]$ ./as6

=========================================
                MENU                    
=========================================
1.Successive Addition
2.Shift and Add Method
3.Exit
1
Enter the value for the first number multiplicand
09
Enter the value for the second number multiplier
11
0099
=========================================
                MENU                    
=========================================
1.Successive Addition
2.Shift and Add Method
3.Exit
2
Enter the value for the first number multiplicand
32
Enter the value for the second number multiplier
10
0320
=========================================
                MENU                    
=========================================
1.Successive Addition
2.Shift and Add Method
3.Exit
3
[secomp@localhost as6]$