Recommendation for declaring constants

[vmorilla]

Are there good practices for declaring constants in z88dk? I have tried the following three options:

a) Using #define:

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#define SCRM_TEXT1 0x1000
set_screen_mode(SCRM_TEXT1);

Obviously works, but in the assembler code produced there is no trace of 'SCRM_TEXT', so it becomes hard to debug:

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	ld	hl,0x1000
	call	_screen_mode

b) using const:

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const uint16_t SCRM_TEXT1 = 0x1000;
set_screen_mode(SCRM_TEXT1);

Which produces less efficient code:

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	ld	hl, (_SCRM_TEXT1)
	call	_screen_mode

c) using enums:

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typedef enum ScreenModeEnum {
    SCRM_TEXT1 = 0x1000
} ScreenMode;

which produces similar results to the first option: no trace of SCRM_TEXT in the generated code:

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	ld	hl,0x1000
	call	_screen_mode

What I would to achieve is the following kind of result:

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SCRM_TEXT1   equ  0x1000
		      
		ld hl, SCRM_TEXT1
		call _screen_mode

Any suggestion?

Thanks!

[dom]

My preferred way is #define or enums, but you can achieve what you want this way:

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extern __at(0x1000) int SCRM_TEXT1;

extern void screenmode(int);

void func()
{
   screenmode((int)&SCRM_TEXT1);
}

And several permutations of similar ideas.

[vmorilla]

Thank you. Is there any possibility of defining such constants in assembler and using them in C. If this is the case, would the code generated improve in any way?

[dom]

It's the same pattern - we use this one in the library to pass link time values from the crt to the library. The generated code is the same as my previous example.

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; Assembler file

PUBLIC _SCRM_TEXT1
defc _SCRM_TEXT1 = 0x1000

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// C file

extern void screenmode(int);

extern void *SCRM_TEXT1;
#define SCRM_TEXT1 (int)&SCRM_TEXT1

void func()
{
   screenmode(SCRM_TEXT1);
}

[vmorilla]

Thank you!

[jorgegv]

It's the same pattern - we use this one in the library to pass link time values from the crt to the library. The generated code is the same as my previous example.

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; Assembler file

PUBLIC _SCRM_TEXT1
defc _SCRM_TEXT1 = 0x1000

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// C file

extern void screenmode(int);

extern void *SCRM_TEXT1;
#define SCRM_TEXT1 (int)&SCRM_TEXT1

void func()
{
   screenmode(SCRM_TEXT1);
}

Nice trick Dom. In this case, int and void* are both 16-bits, but what about constants that are just 8 bits? Are DEFC always defined as 16-bit numbers, and I should just change the (int) in the #define for a (uint8_t), for example?

[jorgegv]

I mean this:

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public _VAL8
defc _VAL8 = 0x25

And then:

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extern void *VAL8;
#define VAL8 (uint8_t)&VAL8