Bitfields are no longer limited to 8 bits! Yay!

stryd_one · February 11, 2008, 2:14pm

Hi guys,

Good news, I have just tested a 15-bit bitfield (15, not 16, to test correct alignment of odd sizes across bytes), and all accesses are correct

This was with a post 2.7.0 SDCC release.

AC and I have been warning people of this limitation for years now, I had to add this info to lots of old threads which are used as references in the wiki and such. Ugh!

Definition looks like this:

typedef union {

struct {

unsigned ALL:15;

}

struct {

unsigned test1:1;

unsigned test2:1;

unsigned test3:1;

unsigned test4:1;

unsigned test5:1;

unsigned test6:1;

unsigned test7:1;

unsigned test8:1;

unsigned test9:1;

unsigned test10:1;

unsigned test11:1;

unsigned test12:1;

unsigned test13:1;

unsigned test14:1;

unsigned test15:1;

}

} bitfield_t;

I tested it by sending notes depending on the bits 6,7,8 and 14 (test7, test8, test9 and test15).

More useless info brought to you by stryd_one ;D

audiocommander · February 11, 2008, 2:37pm

jipee

have you also tested bitfields > 15 entries?

Best,

Michael

stryd_one · February 11, 2008, 2:44pm

I haven’t yet, but I suspect they will be almost unlimited… The output ASM is pretty simple, it just uses for EG:

BTFSC (_bitfield) ,6 for bit 6

or

BTFSC (_bitfield +1) ,4 for bit 12

That’s from memory… I’ll test it with some really silly big bitfields tomorrow night, and paste the code.

stryd_one · February 12, 2008, 2:31pm

Yeh, sweet. Our new limit looks like… a whole bank LOL

typedef union {
    struct {
        unsigned ALL:8;
        };
    struct {
        unsigned test1:1;
        unsigned test2:1;
        unsigned test3:1;
        unsigned test4:1;
        unsigned test5:1;
        unsigned test6:1;
        unsigned test7:1;
        unsigned test8:1;
        unsigned test9:1;
        unsigned test10:1;
        unsigned test11:1;
        unsigned test12:1;
        unsigned test13:1;
        unsigned test14:1;
        unsigned test15:1;
        unsigned test16:1;
        unsigned test17:1;
        unsigned test18:1;
        unsigned test19:1;
        unsigned test20:1;
        unsigned test21:1;
        unsigned test22:1;
        unsigned test23:1;
        unsigned test24:1;
        unsigned test25:1;
        unsigned test26:1;
        unsigned test27:1;
        unsigned test28:1;
        unsigned test29:1;
        unsigned test30:1;
        unsigned test31:1;
        unsigned test32:1;
        unsigned test33:1;
        unsigned test34:1;
        unsigned test35:1;
        unsigned test36:1;
        unsigned test37:1;
        unsigned test38:1;
        unsigned test39:1;
        unsigned test40:1;
        unsigned test41:1;
        unsigned test42:1;
        unsigned test43:1;
        unsigned test44:1;
        unsigned test45:1;
        unsigned test46:1;
        unsigned test47:1;
        unsigned test48:1;
        unsigned test49:1;
        unsigned test50:1;
        unsigned test51:1;
        unsigned test52:1;
        unsigned test53:1;
        unsigned test54:1;
        unsigned test55:1;
        unsigned test56:1;
        unsigned test57:1;
        unsigned test58:1;
        unsigned test59:1;
        unsigned test60:1;
        unsigned test61:1;
        unsigned test62:1;
        unsigned test63:1;
        unsigned test64:1;
        unsigned test65:1;
        unsigned test66:1;
        unsigned test67:1;
        unsigned test68:1;
        unsigned test69:1;
        };
} testbits_t;

testbits_t mybitfield;

void MPROC_NotifyReceivedEvnt(unsigned char evnt0, unsigned char evnt1, unsigned char evnt2) __wparam
{


if (evnt0 == 0x92) {


    mybitfield.test6 = 0;
    mybitfield.test15 = 0;
    mybitfield.test55 = 0;


};

if (evnt0 == 0x93) {


    mybitfield.test6 = 1;
    mybitfield.test15 = 1;
    mybitfield.test55 = 1;


};


if (evnt0 == 0x91) {



if (mybitfield.test55) {
MIOS_MIDI_TxBufferPut(0x90);
MIOS_MIDI_TxBufferPut(0x55);
MIOS_MIDI_TxBufferPut(0x7f);
};

if (mybitfield.test15) {
MIOS_MIDI_TxBufferPut(0x90);
MIOS_MIDI_TxBufferPut(0x15);
MIOS_MIDI_TxBufferPut(0x7f);
};

if (mybitfield.test6) {
MIOS_MIDI_TxBufferPut(0x90);
MIOS_MIDI_TxBufferPut(0x06);
MIOS_MIDI_TxBufferPut(0x7f);
};





};

}

It’s ugly, but it works!:

            udata_main_0      udata  0x000080      data  0x000009

              _mybitfield  0x000080      data    extern _output\main.asm

; Starting pCode block
S_main__MPROC_NotifyReceivedEvnt	code
_MPROC_NotifyReceivedEvnt:
;	.line	143; main.c	void MPROC_NotifyReceivedEvnt(unsigned char evnt0, unsigned char evnt1, unsigned char evnt2) __wparam
	MOVFF	FSR2L, POSTDEC1
	MOVFF	FSR1L, FSR2L
	MOVFF	r0x00, POSTDEC1
	MOVWF	r0x00
;	.line	147; main.c	if (evnt0 == 0x92) {
	MOVF	r0x00, W
	XORLW	0x92
	BNZ	_00126_DS_
_00146_DS_:
	BANKSEL	_mybitfield
;	.line	150; main.c	mybitfield.test6 = 0;
	BCF	_mybitfield, 5, B
; removed redundant BANKSEL
;	.line	151; main.c	mybitfield.test15 = 0;
	BCF	(_mybitfield + 1), 6, B
; removed redundant BANKSEL
;	.line	152; main.c	mybitfield.test55 = 0;
	BCF	(_mybitfield + 6), 6, B
_00126_DS_:
;	.line	157; main.c	if (evnt0 == 0x93) {
	MOVF	r0x00, W
	XORLW	0x93
	BNZ	_00128_DS_
_00148_DS_:
	BANKSEL	_mybitfield
;	.line	160; main.c	mybitfield.test6 = 1;
	BSF	_mybitfield, 5, B
; removed redundant BANKSEL
;	.line	161; main.c	mybitfield.test15 = 1;
	BSF	(_mybitfield + 1), 6, B
; removed redundant BANKSEL
;	.line	162; main.c	mybitfield.test55 = 1;
	BSF	(_mybitfield + 6), 6, B
_00128_DS_:
;	.line	168; main.c	if (evnt0 == 0x91) {
	MOVF	r0x00, W
	XORLW	0x91
	BNZ	_00137_DS_
_00150_DS_:
	BANKSEL	(_mybitfield + 6)
;	.line	172; main.c	if (mybitfield.test55) {
	BTFSS	(_mybitfield + 6), 6, B
	BRA	_00130_DS_
;	.line	173; main.c	MIOS_MIDI_TxBufferPut(0x90);
	MOVLW	0x90
	CALL	_MIOS_MIDI_TxBufferPut
;	.line	174; main.c	MIOS_MIDI_TxBufferPut(0x55);
	MOVLW	0x55
	CALL	_MIOS_MIDI_TxBufferPut
;	.line	175; main.c	MIOS_MIDI_TxBufferPut(0x7f);
	MOVLW	0x7f
	CALL	_MIOS_MIDI_TxBufferPut
_00130_DS_:
	BANKSEL	(_mybitfield + 1)
;	.line	178; main.c	if (mybitfield.test15) {
	BTFSS	(_mybitfield + 1), 6, B
	BRA	_00132_DS_
;	.line	179; main.c	MIOS_MIDI_TxBufferPut(0x90);
	MOVLW	0x90
	CALL	_MIOS_MIDI_TxBufferPut
;	.line	180; main.c	MIOS_MIDI_TxBufferPut(0x15);
	MOVLW	0x15
	CALL	_MIOS_MIDI_TxBufferPut
;	.line	181; main.c	MIOS_MIDI_TxBufferPut(0x7f);
	MOVLW	0x7f
	CALL	_MIOS_MIDI_TxBufferPut
_00132_DS_:
	BANKSEL	_mybitfield
;	.line	184; main.c	if (mybitfield.test6) {
	BTFSS	_mybitfield, 5, B
	BRA	_00137_DS_
;	.line	185; main.c	MIOS_MIDI_TxBufferPut(0x90);
	MOVLW	0x90
	CALL	_MIOS_MIDI_TxBufferPut
;	.line	186; main.c	MIOS_MIDI_TxBufferPut(0x06);
	MOVLW	0x06
	CALL	_MIOS_MIDI_TxBufferPut
;	.line	187; main.c	MIOS_MIDI_TxBufferPut(0x7f);
	MOVLW	0x7f
	CALL	_MIOS_MIDI_TxBufferPut
_00137_DS_:
	MOVFF	PREINC1, r0x00
	MOVFF	PREINC1, FSR2L
	RETURN

So why a whole bank? cause it does the arithmetic pre-assembly, and optimises out any banksels. I don’t see why it couldn’t access like (_mybitfield + 20) hahah. Something of note:

typedef union {
    struct {
        unsigned ALL:8;
        };
    struct {
        unsigned test1:1;
        unsigned test2:1;
        unsigned test3:1;
        unsigned test4:1;
.........

This works. If you make it ALL:69, it says that each field has a 16 bit max. So ALL:16 is good, ALL:17 bad.

But the rest is happy

Edit: I chose 69 because I wanted to go higher than 64, and that’s how it pasted out. I am not a pervert. Well, I am. But that’s not why I chose 69.

audiocommander · February 12, 2008, 6:18pm

I am not a pervert. Well’ date=’ I am. But that’s not why I chose 69. [/quote’]

ohhhh, I know you are… :

nudge nudge, say no more! Say no more! hehehehehehe ;D

and now for something completely different:

I’m really happy about loosing this 8-bit restriction! Thanks for testing & sharing! =)

stryd_one · February 13, 2008, 8:31am

eh? eh? *click click*

LOL

stryd_one · July 30, 2008, 5:05pm

AAaaaaand we’re back to 8 bits:

SDCC pic16 port error: the port currently does not support *reading*
bitfields of size >=8. Instead of generating wrong code, bailling out...
make: *** [_output/main.o] Error 1

That’s erroneous, it doesnt support >8 (=8 is ok)

lylehaze · July 30, 2008, 10:27pm

The first thing you need to ask yourself is:

How many people can get excited about a bitfield?

Then you need to ask, and how many friends can they share their excitement with?

The internet is truly making the world a global village.

LyleHaze

stryd_one · July 31, 2008, 9:00am

Bitfield obsessed coding geek loner hermits of the world, UNITE!

nILS · August 3, 2008, 1:37am

[me=nILS Podewski]cues comic-style trumpet clip: “mwuah mwuah mwuaaaaaaaaaaaaaah”[/me]