ARM VERSION 1.2 manual Setting up a C-type structure, Is equivalent to the C code

Writing ARM and Thumb Assembly Language

Setting up a C-type structure

There are two stages to using structures in C:

1.Declaring the fields that the structure contains.

2.Generating the structure in memory and using it.

For example, the following typedef statement defines a point structure that contains three float fields named x, y and z, but it does not allocate any memory. The second statement allocates three structures of type Point in memory, named origin, oldloc, and newloc:

typedef struct Point

{

float x,y,z; } Point;

Point origin,oldloc,newloc;

The following assembly language code is equivalent to the typedef statement above:

PointBase	RN	r11
	MAP	0,PointBase
Point_x	FIELD	4
Point_y	FIELD	4
Point_z	FIELD	4

The following assembly language code allocates space in memory. This is equivalent to the last line of C code:

origin SPACE 12 oldloc SPACE 12 newloc SPACE 12

You must load the base address of the data structure into the base register before you can use the labels defined in the map. For example:

LDR	PointBase,=origin
MOV	r0,#0
STR	r0,Point_x
MOV	r0,#2
STR	r0,Point_y
MOV	r0,#3
STR	r0,Point_z

is equivalent to the C code:

origin.x = 0; origin.y = 2; origin.z = 3;

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