Translating the
variable definition: the
head
variable
- In Java,
we define
the head
variable as
follows:
public class Node
{
int value;
List next;
}
Node head;
|
- In C,
we define
the head
variable as
follows:
struct Node
{
int value;
struct Node *next;
}
struct Node *head;
|
- The
variable head is
a
reference variable
that stores
a
memory address (= 4 bytes)
|
Translating the
variable definition: the
head
variable
- The
translation of
the
definition
of the variable
head
into
ARM assembler
is
as
follows:
.data
head: .skip 4 // The head variable
|
-
Note:
the variable at
label
head is
reference
(= address)
(and not a
Node object):
|
How to fetch the
address stored
in the variable
head
- Facts about the
variable
head:
- The variable
head is
stored in
memory
- The variable
head
contains
4 bytes
|
|
How to fetch the
address stored
in the variable
head
- Facts about the
variable
head:
- The variable
head is
stored in
memory
- The variable
head
contains
4 bytes
|
-
Therefore, we must use the
ldr
instruction
to fetch
4 bytes in
the variable head:
// Preparation:
// r1 = address of head
ldr r0, [r1]
|
|
We have (already) learned
how to
put the
address of
head in
a register !
How to fetch the
base address stored
in the variable
head
- Facts about the
variable
head:
- The variable
head is
stored in
memory
- The variable
head
contains
4 bytes
|
- How to
fetch
the
address in
the
variable
head into
a register
(e.g.: r0):
// Preparation:
movw r1, #:lower16:head
movt r1, #:upper16:head
ldr r0, [r1]
|
|
Note:
exactly the
same way as
fetching
an
int typed variable
from memory !!
Difference in
fetching the base address of
a static array and the
first object in
a linked list
|
Base address of
a
static
array
|
Base address of
the
first
list object
|
|
|
|
The base address of a
static array
is a
constant number
|
The base address of the
first
list object
is a
variable
|
The same technique is used
to implement the
dynamic array
|
Base address of
a
static
array
|
Base address of
a
dynamic
array
|
|
|
|
The base address of a
static array
is a
constant number
|
The base address of a
dynamic
array
is a
variable
|
I.e.:
you can use this
method to
fetch the
base address of a
dynamic array
❮
❯