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AN669

Embedding Assembly Routines into C Language Using a Floating Point Routine as an Example

Microchip Technology 

AN669

Assembly Language Variables, Include Files,

etc.

For the floating point math routines of AN575, there is

one include file which contains important constant and

register declarations: math16.inc. This file of declara-

tions is rather extensive, however, it is straightforward

to convert it to C. Example 4 shows a segment of the

math16.inc requiring some attention for the conver-

sion.

EXAMPLE 4: MATH16.INC EXCERPT

FROM AN575. ASSEMBLY

LANGUAGE FILE

These Constant and Variable Declarations

Need to be Converted to C Language

Declarations

Example 5 shows the equivalent C constant and vari-

able declarations. The equates in assembly language

create constants. The equivalent C language is a

#define. Moreover, variables are declared in assem-

bly language by equating a variable name to a register

RAM location (i.e. AARGB7 equ 0x20). In C the vari-

ables are declared by assigning a type to the variable.

In the listing in Example 5, AARGB7 is declared as an

unsigned integer data type.

B0

equ

B1

equ

B2

equ

B3

equ

B4

equ

B5

equ

B6

equ

B7

equ

MSB

equ

LSB

equ

.

. etc.

.

AARGB7 equ

AARGB6 equ

AARGB5 equ

AARGB4 equ

AARGB3 equ

AARGB2 equ

AARGB1 equ

AARGB0 equ

AARG equ

0

1

2

3

4

5

6

7

7

0

0x20

0x21

0x22

0x23

0x24

0x25

0x26

0x27

0x27

; most significant

; byte of argument A

EXAMPLE 5: THE CONVERTED MATH16C.C FILE. C LANGUAGE FILE

#define B0

0

#define B1

1

#define B2

2

#define B3

3

#define B4

4

#define B5

5

#define B6

6

#define B7

7

#define MSB 7

#define LSB 0

.

. etc.

.

unsigned int AARGB0 @ ACCB0;

unsigned int AARGB1 @ ACCB1;

unsigned int AARGB2 @ ACCB2;

unsigned int AARGB3 @ ACCB3;

unsigned int AARGB4 @ ACCB4;

unsigned int AARGB5 @ ACCB5;

unsigned int AARGB6 @ ACCB6;

unsigned int AARGB7 @ ACCB7;

unsigned int AARG @ ACC;

// most significant byte of argument A

// least significant byte of argument A

// most significant byte of argument A

© 1997 Microchip Technology Inc.

DS00669A-page 3

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