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Source: Mastering Embedded Systems

1. Prevent a header file from being included multiple times

1#ifndef COMDEF_H
2#define COMDEF_H
3// Header file content
4#endif

2. Redefine some types to prevent differences in type byte sizes due to various platforms and compilers, facilitating portability.

1typedef unsigned char boolean; /* Boolean value type. */
2typedef unsigned long int uint32; /* Unsigned 32 bit value */
3typedef unsigned short uint16; /* Unsigned 16 bit value */
4typedef unsigned char uint8; /* Unsigned 8 bit value */
5typedef signed long int int32; /* Signed 32 bit value */
6typedef signed short int16; /* Signed 16 bit value */
7typedef signed char int8; /* Signed 8 bit value */

Not recommended:

 1typedef unsigned char byte; /* Unsigned 8 bit value type. */
 2typedef unsigned short word; /* Unsigned 16 bit value type. */
 3typedef unsigned long dword; /* Unsigned 32 bit value type. */
 4typedef unsigned char uint1; /* Unsigned 8 bit value type. */
 5typedef unsigned short uint2; /* Unsigned 16 bit value type. */
 6typedef unsigned long uint4; /* Unsigned 32 bit value type. */
 7typedef signed char int1; /* Signed 8 bit value type. */
 8typedef signed short int2; /* Signed 16 bit value type. */
 9typedef long int int4; /* Signed 32 bit value type. */
10typedef signed long sint31; /* Signed 32 bit value */
11typedef signed short sint15; /* Signed 16 bit value */
12typedef signed char sint7; /* Signed 8 bit value */

3. Get a byte or word at a specified address

1#define MEM_B( x ) ( *( (byte *) (x) ) )
2#define MEM_W( x ) ( *( (word *) (x) ) )

4. Calculate maximum and minimum values

1#define MAX( x, y ) ( ((x) > (y)) ? (x) : (y) )
2#define MIN( x, y ) ( ((x) < (y)) ? (x) : (y) )

5. Get the offset of a field in a structure

1#define FPOS( type, field ) \
2/*lint -e545 */ ( (dword) &(( type *) 0)-> field ) /*lint +e545 */

6. Get the size in bytes of a field in a structure

1#define FSIZ( type, field ) sizeof( ((type *) 0)->field )

7. Convert two bytes to a word in LSB format

1#define FLIPW( ray ) ( (((word) (ray)[0]) * 256) + (ray)[1] )

8. Convert a word to two bytes in LSB format

1#define FLOPW( ray, val ) \
2(ray)[0] = ((val) / 256); \
3(ray)[1] = ((val) & 0xFF)

9. Get the address of a variable (word width)

1#define B_PTR( var ) ( (byte *) (void *) & (var) )
2#define W_PTR( var ) ( (word *) (void *) & (var) )

10. Get the high and low byte of a word

1#define WORD_LO(xxx) ((byte) ((word)(xxx) & 255))
2#define WORD_HI(xxx) ((byte) ((word)(xxx) >> 8))

11. Return the nearest multiple of 8 greater than X

1#define RND8( x ) ((((x) + 7) / 8 ) * 8 )

12. Convert a letter to uppercase

1#define UPCASE( c ) ( ((c) >= 'a' && (c) <= 'z') ? ((c) - 0x20) : (c) )

13. Check if a character is a decimal digit

1#define DECCHK( c ) ((c) >= '0' && (c) <= '9')

14. Check if a character is a hexadecimal digit

1#define HEXCHK( c ) ( ((c) >= '0' && (c) <= '9') ||\
2((c) >= 'A' && (c) <= 'F') ||\
3((c) >= 'a' && (c) <= 'f') )

15. A method to prevent overflow

1#define INC_SAT( val ) (val = ((val)+1 > (val)) ? (val)+1 : (val))

16. Return the number of elements in an array

1#define ARR_SIZE( a ) ( sizeof( (a) ) / sizeof( (a[0]) ) )

17. Return the value of an unsigned number n mod by power of two (X,n)=X%(2^n)

1#define MOD_BY_POWER_OF_TWO( val, mod_by ) \
2( (dword)(val) & (dword)((mod_by)-1) )

18. For IO space mapped in storage space, input and output processing:

1#define inp(port) (*((volatile byte *) (port)))
2#define inpw(port) (*((volatile word *) (port)))
3#define inpdw(port) (*((volatile dword *)(port)))
4#define outp(port, val) (*((volatile byte *) (port)) = ((byte) (val)))
5#define outpw(port, val) (*((volatile word *) (port)) = ((word) (val)))
6#define outpdw(port, val) (*((volatile dword *) (port)) = ((dword) (val)))

19. Use some macros for debugging

The ANSI standard specifies five predefined macro names, which are:

1_ L I N E _
2_ F I L E _
3_ D A T E _
4_ T I M E _
5_ S T D C _

If the compilation is not standard, it may only support a few of the above macro names, or not support them at all. Remember that the compiler may also provide other predefined macro names.<span>_ L I N E _</span> and <span>_ F I L E _</span> macros have been discussed in the section regarding <span># l i n e</span>, here we discuss the remaining macro names.<span>_ D A T E _</span> macro contains a string in the form of month/day/year, indicating the date when the source file was translated into code.The time when the source code is translated into target code is included as a string in <span>_ T I M E _</span>. The string is in the form of hour:minute:second.If the implementation is standard, the macro <span>_ S T D C _</span> contains the decimal constant 1. If it contains any other number, the implementation is non-standard.Macros can be defined, for example: when <span>_DEBUG</span> is defined, output data information and the line number in the file.

1#ifdef _DEBUG
2#define DEBUGMSG(msg,date) printf(msg);printf(“%d%d%d”,date,_LINE_,_FILE_)
3#else
4#define DEBUGMSG(msg,date)
5#endif

20. Macro definitions to prevent errors when used should be enclosed in parentheses.

For example:

1#define ADD(a,b) (a+b)

Use <span>do{}while(0)</span> statement to enclose multiple statements to prevent errors, for example:

1#difne DO(a,b) a+b;\
2a++;

When applied:

1if(….)
2DO(a,b); // produces an error
3else

Solution:

1#define DO(a,b) do{a+b;\
2a++;}while(0)

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