AW: [Sdcc-user] bitaddressable variables

[<MSoegtrop@Michael-Soegtrop.de>]

Hello Karl,

ANSI C for your modula bits code looks like this:

struct SButtons {
	unsigned up:1;
	unsigned down:1;
	unsigned left:1;
	unsigned right:1;
} buttons;

int main() {
	buttons.left=3D1;

	if(buttons.left) {
		// do something
	}
}

The :1 after each member is the number of bits to assign to this member (=
can
be any number of bits up to the machines wordsize). If the field is signe=
d,
the possible values are 0 and -1, if the field is unsigned, the possible
values are 0 and 1.

I don't know whether SDCC supports this kind of syntax, but probably it
does, because it is very convenient for saving memory. If you try it, ple=
ase
let me know the results. If SDCC does not support this syntax, the best w=
ay
is to use an enum or defines to define bitmasks, and to use bit operators=
 (&
and |).

Regards, Michael

-----Urspr=FCngliche Nachricht-----
Von: sdc...@li...
[mailto:sdc...@li...]Im Auftrag von karl
mowatt-wilson
Gesendet: Sonntag, 8. Juli 2001 13:54
An: sdc...@li...
Betreff: [Sdcc-user] bitaddressable variables


I am translating some code I wrote & tweaked under Modula-51 to compile w=
ith
SDCC (I am new to C).  This is for reading/debouncing/using a set of
buttons.  Under Modula-51 I could have some variable declarations such as
this:

VAR
   buttons      : BYTE BITADDRESSABLE;
   button_up    : BOOLEAN AT buttons.0;
   button_down  : BOOLEAN AT buttons.1;
   button_left  : BOOLEAN AT buttons.2;
   button_right : BOOLEAN AT buttons.3;

This would declare the variable 'buttons' to be somewhere in the range 0x=
20
to 0x2F (I don't care where, just as long as the compiler/linker/whatever
knows).  The variables 'button_up', 'button_down', etc. would be assigned=
 as
bit variables pointing to the bits within the bitaddressable variable
'buttons'.
ie. if buttons is at 0x23 then button_up would be bit address 0x18,
button_down would be bit address 0x19, etc.

I could then read the set of buttons (assuming they're all on P1 and need=
 no
debouncing) and make use of them something like this:

   buttons :=3D P1;
   IF button_up   THEN do_something;
   IF button_down THEN do_somethingelse;

This generated clean & efficient assembler.  How do I do something which
will generate the same nice sort of code in SDCC?

thanks,
Karl.
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