Slide 13.2: Local variables

Local Variables (Cont.)

Local variables are created on the runtime stack. They can not be given default values at assembly time, but they can be initialized at runtime. The following examples calculate a geometric series:

      a×r^n-1 + ... + a×r³ + a×r² + a×r¹ + a
    = 3×2³ + 3×2² + 3×2¹ + 3

Using Global Variables

Using Local Variables

 INCLUDE Irvine32.inc
 a = 3
 r = 2
 n = 4         ; n > 1

 .data
     result  SDWORD  0
     count    DWORD  ?
     r1      SDWORD  ?
     prod    SDWORD  ?

 .code
 main PROC
     mov   ecx, n
     dec   ecx
 L1: mov   count, ecx
     call  calc
    
     
      
     

     
    
    
    


    
     
     
    
        add   result, eax
     loop  L1
     add   result, a
     mov   eax, result
     call  WriteInt
     exit
 main ENDP

 ;; Calculate a×r**n
 calc PROC
     mov   r1, r
     mov   eax, a
     ;; EAX: multiplicand
 L1: imul  r1
     loop  L1
     mov   ecx, count
     mov   prod, eax  ; EAX: product
     ret
 calc ENDP
 END main

 INCLUDE Irvine32.inc
 a = 3
 r = 2
 n = 4         ; n > 1

 .data
     count    DWORD  ?
     prod    SDWORD  ?

 .code
 main PROC
     LOCAL  var:SDWORD
     mov    var, 0
     mov    ecx, n
     dec    ecx
 L1: mov    count, ecx
     call   calc
    
     
      
     
     
    
    
    


    
     
     
    
        add    var, eax
     loop   L1
     add    var, a
     mov    eax, var
     call   WriteInt
     exit
 main ENDP

 ;; Calculate a×r**n
 calc PROC
     LOCAL  var:SDWORD
     mov   var, r
     mov   eax, a
     ;; EAX: multiplicand
 L1: imul  var
     loop  L1
     mov   ecx, count
     mov   prod, eax  ; EAX: product
     ret
 calc ENDP
 END main