Chapter 8 - Advanced Procedures

Global variables - are declared in the .data segment and exist throughout the duration of the program.

Local variables - are created and destroyed during a single procedure.

Advantages of local variables include:

Limited access which helps in debugging
Allow efficient use of memory
Allows multiple name use in separate procedures

LOCAL directive The LOCAL directive declares one or more local variables and must be placed (if used) immediately following a PROC directive. The general form is:

LOCAL varlist

where varlist is a list of variables of the form label:type

Examples include:

MyProc1 PROC
        LOCAL v1:BYTE

MyProc2 PROC
        LOCAL temp:DWORD, flag:BYTE

MyProc3 PROC
        LOCAL name[10]:BYTE

Let's examine the automatic code generation for:

BubbleSort PROC
           LOCAL temp:DWORD, SwapFlag:BYTE

as described on p. 262

Note: If you are going to have local arrays of any size, make sure you've allocated enough stack space such as: .stack 8192

INVOKE directive The INVOKE directive allows arguments to be passed to the procedure. The general syntax is:

INVOKE procName [,argument(s)]

Let's look at INVOKE AddTwo, val1, val2 on p. 265.

Now let's examine the following program:


TITLE CalcSum Program                   (Csum.asm)

INCLUDE Irvine32.inc

.stack 4096

.data
x1 byte 1
y1 byte 3

.code
CalcSum PROC x:byte, y:byte
  LOCAL temp:byte

  mov al,x
  add al,y
  mov temp,al
  add al,temp
L2:	ret
CalcSum ENDP

main PROC
  mov eax,0
  INVOKE CalcSum , x1, y1
  call WriteDec
  call Crlf
  exit
main ENDP
end Main

P1: Show the stack before the instruction mov al,x is executed.

Let's examine the ArraySum example on p. 269.

a Finally, let's examine passing by value vs passing by reference on p. 270.