datasg  segment para'code'
    msg1    db  'enter a number:',"$"
    msg2    db  'the log of this number is:',"$"
    count   db  0
    sign    dw  ?
    string  db  6 dup( ' '),"$"
    sign1   db  ?
    number  dw  ?
    strlist label   byte    
    max     db  20
    len     db  ?
    buffer  db  20 dup(' ')
    dolar   db  '$'
    datasg  ends
    codesg  segment para 'code'
        main    proc    far
                assume  ds:datasg,cs:codesg
                mov     ax,datasg
                mov     ds,ax
                mov     ah,6h
                mov     al,25
                mov     ch,0
                mov     cl,0
                mov     dh,24
                mov     dl,79
                mov     bh,7
                int     10h
                mov     ah,2h
                mov     dh,10
                mov     dl,30
                mov     bh,0
                int     10h
                lea     dx,msg1
                mov     ah,9h
                int     21h
                mov     ah,0ah
                lea     dx,strlist
                int     21h
                lea     bx,buffer
   while_blank:cmp      byte  ptr[bx],' '
                jne     end_while_blank
                inc     bx
                jmp     while_blank
   end_while_blank:
                mov     sign,1
                cmp     byte ptr[bx],'+'
                je      skip_sign
                cmp     byte ptr[bx],'_'
                jne     save_sign
                mov     sign,-1
   skip_sign:   inc     bx
   save_sign:   mov     ax,0
                mov     count,0
   while_digit: cmp     byte ptr [bx],'0'
                jl      end_while_digit
                cmp     byte ptr [bx],'9'
                jg      end_while_digit
                mov     cx,10
                mul     cx
                mov     cl,[bx]
                and     cx,000fh
                add     ax,cx
                inc     count
                inc     bx 
                jmp     while_digit
  end_while_digit:
                imul    sign
  ;;;;;;;;;;;compute log;;;;;;;;;;;
                mov     number,ax
                mov     cx,0
                mov     ax,1
  lopwhile:     cmp     ax,number
                jnle    end_while
                add     ax,ax
                inc     cx
                jmp     lopwhile
  end_while:    dec     cx
                mov     ax,cx
 ;;;;;;;;;;;convert number in ax to string;;;;;;;
                lea     bx,string
                add     bx,5
                mov     sign,' '
                cmp     ax,0
                jge     setup
                mov     sign1,'-'
                neg     ax
   setup:       mov     cx,10
   divloop:     mov     dx,0
                div     cx
                add     dl,30h
                mov     [bx],dl
                dec     bx
                cmp     ax,0
                jne     divloop
                mov     cl,sign1
                mov     [bx],cl
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
                mov     ah,2h
                mov     dh,12
                mov     dl,30
                mov     bh,0
                int     10h
                ;print result 
                lea     dx,msg2
                mov     ah,9h
                int     21h
                lea     dx,string
                mov     ah,9h
                int     21h
 ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
                mov     ax,4c00h
                int     21h
  main          endp
  codesg        ends
                end     main