Dudes:

John Payson accidentally sent the following message to me directly;
I'm forwarding it to the PICLIST.

-Andy

------- Forwarded Message Follows -------

From:          John Payson <supercat@Mcs.Net>
Subject:       Re: Bit Number to Bit Mask Question
To:            fastfwd@ix.netcom.com
Date:          Wed, 17 Sep 1997 16:39:38 -0500 (CDT)


> > Using a PIC, has anybody figured out a good way to take a number
> > from zero to seven (0 to 7) and use it to generate the
> > corresponding bit mask (i.e., 00000001, 00000010, 00000100, etc.)?
>
> Frank:
>
> Every time I'm faced with this problem, I spend a few minutes trying
> to find a method that's better than a lookup table... So far, I
> haven't found one.

Hmm...
 movlw  $01
 btfsc  BITNUM,1
  movlw $04
 movwf  temp
 bcf    C
 btfsc  BITNUM,0
 rlf    temp
 movf   temp,w
 btfsc  BITNUM,2
  swapf temp,w

Not terribly encouraging (10 words/10 cycles).  Maybe...

 movlw  $FF
 btfsc  BITNUM,0
  andlw $AA
 btfsc  BITNUM,1
  andlw $CC
 btfsc  BITNUM,2
  andlw $F0
 movwf  temp
 comf   temp
 incf   temp
 andwf  temp,w

Interesting, but even worse (unless I'm missing an optimization on
that ending part).  Anyone see any improvements for those two methods
above?

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