Re: [avr-gcc-list] efficiency of assigning bits

[E. Weddington]

Jamie Morken wrote:

> Hi,
>
> I am trying to turn two bits off on a port as
> quickly as possible, how do these two methods
> compare:
>
> PORTD = (PORTD & ~PD1) & ~PD4;
>
> or:
>
> cbi(PORTD, PD1); 
> cbi(PORTD, PD4);
>
>  
cbi is deprecated and no longer exists in the latest release of avr-libc.

> I am assuming these are equivalent.
>  

Not quite. Do this:

PORTD &= ~(_BV(PD1) | _BV(PD4));

That will clear the two bits at the same time.

Take a look at this thread at the AVR Freaks website for a quick 
tutorial on bit operators in C:
<http://www.avrfreaks.net/index.php?name=PNphpBB2&file=viewtopic&p=40348&highlight=programming+101#40348>