CS255 Syllabus

Accessing Data in Linked List

In this part of the course, I will only show you how to access the data stored in the elements of a linked list
In a later part of the course (where we discuss recursion), I will show you how linked list are manipulated by the computer in more detail.
Example List Structure
I will use the following list structure in my examples:
```
   +-------------+
   |    value    |  <--- contains an integer value
   +-------------+
   |    next     |  <--- contains a reference to the next list element
   +-------------+
```
I also assume that a linked list has already been set up
I will discuss how to manipulate list later, here, all I want to achieve is to show you how the indirect addressing mode is used to access list elements
The following is a list variable and it's definition in assembler:
```
  High level language		Assembler language
  ===================		==================

  List head;                    head: ds.l 1
 
```

Example 1:

  High level language           Assembler language
  ===================           ==================

  int ans;

  answer = head.value;          movea.l  head, a0
				move.l   (a0), ans

Example 2:

  High level language           Assembler language
  ===================           ==================

  int ans;

  answer = head.next.value;     movea.l  head, a0
				movea.l  4(a0), a0
				move.l   (a0), ans

Example 3:

  High level language              Assembler language
  ===================              ==================

  int ans;

  answer = head.next.next.value;    movea.l  head, a0
				    movea.l  4(a0), a0
				    movea.l  4(a0), a0
				    move.l   (a0), ans

Here is an assembler program containing the examples:
- Assembler DEMO program: click here
- To see the linked list, you need the following EGTAPI debug information file: click here