----- Original Message -----
From: <piclist@xargs.com>
To: Microcontroller discussion list - Public. <piclist@mit.edu>
Sent: Thursday, October 07, 2004 7:34 AM
Subject: Re: [PIC] new optimisation in XCSB


> On Wed, 6 Oct 2004, William Chops Westfield wrote:
>
> > Not exactly a fair comparison; He's bragging about the optimizer,
> > not the quality of the original code.
>
> I don't see anything in that code that requires optimization.  It's
> purely constant expressions that can be evaluated at compile time.
>
> > Does the C compiler still only generate 2 instructions when you add
> > an equivalently convoluted "abstraction" of io port bits?
>
> They're almost identically "abstracted" in the compiler's header file:
>
> > hwreg PORTA = 5
> > const RA3 = (&PORTA << 3) + 3
>
> static volatile unsigned char   PORTA   @ 0x05;
> static volatile bit RA3 @ (unsigned)&PORTA * 8 + 3;
>
> > and define functions?  It's a substantial accomplishment, IMO...
>
> The functions were "inline", so they're probably interpreted more like
> C macros than functions.  But something like this:
>
> #define TEST_BIT(port, bit)     (((port) & (1 << ((bit) & 7))) != 0)
> #define SET_BIT(port, bit)      ((port) |= (1 << ((bit) & 7)))
>
> void main(void)
> {
>     if (TEST_BIT(PORTA, 3))
>         SET_BIT(PORTB, 4);
> }
>
> still generates two instructions.
>
> --
> John W. Temples, III

Ok John, the following still generates only 3 instructions.

proc inline set_bit(uint id)
        *(id >> 3) |= (1 << (id & 7))
endproc

proc inline ubyte test_bit(uint id)
        return (*(id >> 3) & (1 << (id & 7))) != 0
endproc

proc fred()

        byte flags

        if test_bit((&flags * 8) + 0) == 1 then
                set_bit((&flags * 8) + 1)
        endif
endproc

I would be grateful if you could tell me how this compares with the Hi-Tech PICC
you are using.

Regards
Sergio Masci

http://www.xcprod.com/titan/XCSB - optimising PIC compiler




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