;These procedures demonstrate the difference between call by address and
;  call by value.
       .model small
       .186
       .stack 100h
       .data
msgValIn      db     "The value of data before calling procedure value is   $"
msgValOut     db     "The value of data after calling procedure value is    $"
msgAddIn      db     "The value of data before calling procedure address is $"
msgAddOut     db     "The value of data after calling procedure address is  $"
data   dw     ?
       .code
include Asm_io.inc
main   proc
       mov    ax,@data
       mov    ds,ax

       call   passByValue
       call   passByAddress

       mov    ax,4c00h
       int    21h
main   endp

passByValue   proc
       push   ax

       mov    data,3
 
       push   offset msgValIn      ;print data before the call
       push   data
       call   writeValue
       add    sp,4

       push   data                 ;pass by value
       call   value
       add    sp,2

       push   offset msgValOut     ;print data after the call
       push   data
       call   writeValue
       add    sp,4

       pop   ax
       ret
passByValue   endp

value  proc
       push   bp
       mov    bp,sp

       mov    word ptr [bp+4],7    ;change the value on the stack

       mov    sp,bp
       pop    bp
       ret
value  endp

passByAddress proc
       push   ax

       mov    data,3
 
       push   offset msgAddIn      ;print data after the call
       push   data
       call   writeValue
       add    sp,4

       push   offset data          ;pass by address
       call   address
       add    sp,2

       push   offset msgAddOut     ;print data after the call
       push   data
       call   writeValue
       add    sp,4

       pop   ax
       ret
passByAddress endp

address       proc
       push   bp
       mov    bp,sp
       push   bx

       mov    bx,[bp+4]            ;get the address of data from the stack
       mov    word ptr [bx],7      ;change the value of data in the data segment

       pop    bx
       mov    sp,bp
       pop    bp
       ret
address       endp

writeValue    proc
       push   bp
       mov    bp,sp
       push   dx
       push   ax

       push   [bp+6]
       call   writeString

       mov    ax,[bp+4]
       call   print_signed

       call   crlf
       
       pop    ax
       pop    dx
       mov    sp,bp
       pop    bp
       ret
writeValue    endp

writeString   proc
       push   bp
       mov    bp,sp
       push   ax
       push   dx

       mov    dx,[bp+4]
       mov    ah,09h
       int    21h

       pop    dx
       pop    ax
       mov    sp,bp
       pop    bp
       ret
writeString   endp

crlf   proc
       push   ax
       push   dx

       mov    ah,02h
       mov    dl,0dh
       int    21h
       mov    dl,0ah
       int    21h

       pop    ax
       pop    dx
       ret
crlf   endp


       end    main