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

[E. Weddington]

Jamie Morken wrote:

>  
>
> > To clear bit 0 and set bits 1,2,3 without disturbing the other bits:
> >
> > PORTD = (PORTD & ~(_BV(0))) | (_BV(1)|_BV(2)|_BV(3));
> >
> >    
>
> Thanks that is working!
>
>  
Great! (*phew* I didn't test it beforehand.)

> I noticed this in the avr-libc usermanual FAQ:
>
> "http://www.nongnu.org/avr-libc/user-manual/FAQ.html#faq_intpromote";
>
> So would it be a good idea (for saving uC time) to convert that above line to 
> this:
>
> PORTD = (PORTD & (unsigned char)~(_BV(0))) | (unsigned 
> char)_BV(1)|_BV(2)|_BV(3));
>  
True. Technically one should do that. I wrote the above line rather quickly.

One could also use the <stdint.h> header and do this:

PORTD = (PORTD & (uint8_t)~(_BV(0))) | (uint8_t)(_BV(1)|_BV(2)|_BV(3)));

At least the type names are a little shorter. Note the extra parentheses around 
the 3 bits on the far right.

Eric