RE: [AVR-Chat] Exclusive or
2004-06-20 by Dave Hylands
Hi Wagner, The following comninations will also yield a 1: 0111 1011 1101 1110 I think that David made a mistake on his 0111 entry. To check that only one bit is set is the same thing as saying that a number is a power of two. If the expression ( x & ( x - 1 )) yields zero, then x is a power of two. -- Dave Hylands Vancouver, BC, Canada http://www.DaveHylands.com/
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> -----Original Message----- > From: wagner [mailto:wagner@ustr.net] > Sent: Sunday, June 20, 2004 11:28 AM > To: AVR-Chat@yahoogroups.com > Subject: Re: [AVR-Chat] Exclusive or > > > David VanHorn wrote: > > What's the fastest way to get the exclusive or, of four bits in a > > register? > > > > 0000 = 0 > > 0001 = 1 > > 0010 = 1 > > 0011 = 0 > > 0100 = 1 > > 0101 = 0 > > 0110 = 0 > > 0111 = 0 > > and so on... > > > > Not for a parity generator, but I think it ends up as the same > > problem. > > > That is a very tricky question. > > If you assume literaly "Exclusive Or" for 4 bits, you are > stating that when JUST ONE bit is UP you will have output UP, > it means, only the following combinations will have output UP: > > 0001 > 0010 > 0100 > 1000 > > I can think of many fancy ways to verify that, including > digital external and even a jaw dropping 5 resistors tied to > 4 output pins to read an analog voltage via an adc to > identify just one output pin up, but not so simply as 4 easy > comparisons for 1, 2, 4 and 8. This could be done in few > different ways, a loop with a binary shifting 4 comparisons, > pure 4 comparisons with fixed values, etc. > > Wagner > > > --- > Outgoing mail is certified Virus Free. > Checked by AVG anti-virus system (http://www.grisoft.com). > Version: 6.0.706 / Virus Database: 462 - Release Date: 6/14/2004 > > > > ------------------------ Yahoo! Groups Sponsor > --------------------~--> > Make a clean sweep of pop-up ads. Yahoo! Companion Toolbar. > Now with Pop-Up Blocker. Get it for free! > http://us.click.yahoo.com/L5YrjA/eSIIAA/yQLSAA/dN_tlB/TM > -------------------------------------------------------------- > ------~-> > > > Yahoo! Groups Links > > > > > > >