ASM program to perform multiplication of two 8-bit hexadecimal numbers.

Statement: -
To perform multiplication of two 8-bit hexadecimal numbers. Use successive addition and add and shift method.
Code:- 

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%macro scall 4 ;macro to take input and output mov rax,%1 mov rdi,%2 mov rsi,%3 mov rdx,%4 syscall %endmacro Section .data title: db 0x0A,"------- Multiplication -----------",0x0A db "1. Multiplication using successive addition", 0x0A db "2. Using ADD and SHIFT ",0x0A db "3. Exit", 0x0A db "Enter your choice: ",0x0A len: equ $-title msg1:db "Enter 1st Number: ",0x0A len1: equ $-msg1 msg2: db "Enter 2nd Number: ", 0x0A len2: equ $-msg2 ans_msg: db "Answer: ", 0x0A ans_len: equ $-ans_msg cnt :db 00H cnt2:db 00H newline:db 0x0A bye: db 0x0A,"***GOOD BYE***",0x0A bye_len:equ $-bye ;---------------------------------------------------------- Section .bss choice resb 4 num1 resb 8 num2 resb 8 hnum1: resb 4 hnum2:resb 4 result: resb 4 ;---------------------------------------------------------- Section .text global main main: ;print menu by macro scall scall 1,1,title,len ;read choice mov rax,0 mov rdi,0 mov rsi, choice mov rdx,2 syscall ;compare choices to act as a switch case cmp byte[choice],'1' JE SUADD cmp byte[choice],'2' je ADDSHIFT cmp byte[choice],'3' jae EXIT jmp main ;========================================================= SUADD: mov rax,1 mov rdi,1 mov rsi, msg1 mov rdx,len1 syscall mov rax,0 mov rdi, 1 mov rsi, num1 mov rdx,8 syscall mov rsi,num1 ;;no1 to converted in hex call AtoH mov [hnum1],bx ;num 2 accept and conversion to hex mov rax, 1 mov rdi,1 mov rsi, msg2 mov rdx, len2 syscall mov rax, 0 mov rdi,0 mov rsi, num2 mov rdx, 8 syscall mov rsi,num2 ;;no to converted call AtoH mov [hnum2],bx ;addition process starteed mov bx,[hnum1] mov cx,[hnum2] mov ax,00H sup:add ax,bx dec cx; jnz sup ;convert result from hex to ascii mov dx,ax mov rdi, result call HtoA scall 1,1,ans_msg,ans_len mov rax, 1 mov rdi,1 mov rsi,result mov rdx,4 syscall scall 1,1,newline,1 jmp main ;========================================================== ADDSHIFT: scall 1,1,msg1,len1 scall 0,1,num1,8 mov rsi,num1 ;;no1 to converted in hex call AtoH mov [hnum1],bx ;num 2 accept and conversion to hex scall 1,1,msg2,len2 scall 0,0,num2,8 mov rsi,num2 ;;no to converted call AtoH mov [hnum2],bx mov byte[cnt],16 mov eax,0000H mov bx,[hnum1] mov cx,[hnum2] TOP: SHL ax,1 ROL bx,1 JNC BELOW ADD ax,cx BELOW: dec byte[cnt] JNZ TOP ;convert result from hex to ascii mov dx,ax mov rdi, result call HtoA scall 1,1,ans_msg,ans_len scall 1,1,result,4 scall 1,1,newline,1 jmp main EXIT: scall 1,1,bye,bye_len mov rax,60 ;exit procedure mov rdi,0 syscall ret AtoH: ;result hex no is in bx mov byte[cnt],04H mov ebx,00H hup: rol ebx,04 mov al,byte[rsi] cmp al,39H JBE HNEXT SUB al,07H HNEXT: sub al,30H add bl,al INC rsi DEC byte[cnt] JNZ hup ret HtoA: ;hex_no to be converted is in dx //result is stored in rdi/user defined variable mov byte[cnt2],04H aup: rol dx,04 mov cl,dl and cl,0FH CMP CL,09H jbe ANEXT ADD cl,07H ANEXT: add cl, 30H mov byte[rdi],cl INC rdi dec byte[cnt2] JNZ aup ;mov rax,1 ;mov rdi,1 ;mov rcx,result ;mov rdx,4 ;syscall ret

Output:-