Factorial for large numbers

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I want to write a x86 masm program that calculates a big factorials (results up to 128 bits), but I am not sure how to do that. I've written a version that calculates up to 32bits, how could I change it up so that it works for larger numbers?

TITLE MASM Template                     (main.asm)

INCLUDE Irvine32.inc

.data
msge byte "Enter number:  ",0;
num dword 0;
.code
main proc
mov edx,offset msge
call writestring    ;print message on Console
call readint    ;used get input from user
mov num,eax ;assign input value to variable 'num'
push num    ;push num in stack
call fact   ;call factorial function for calculalting factorial
call writedec   ;print the factorial on console
call crlf   ;clear screen
    exit
main ENDP   ;end main function

;Factorial function
fact proc
    push ebp    ;push ebp register in stack
    mov ebp,esp ;assing stack pointer 'esp' to the eax register
    mov eax,[ebp+8]
    cmp eax,1   ;compare until number reaches to 1
    je l1   ;jump if equal
    dec eax ;decrement number by 1. if current number is 5 then decrement by 1 and come 4
    push eax ;again push eax number to stack
    call fact
    mov ebx,[ebp+8]
    mul ebx; multply e.g 5*4*3*2*1=120
    l1:
    pop ebp; pop ebp 'base pionter'
    ret 4   ;return the factorial
fact endp
;End factorial function

END main

asked 30 secs ago

user3885166

47

Factorial for large numbers