Post by thread:[PIC]: Counting Bits

I'm unable to search the PICLIST.COM archive, and Jeff Keyser's archive seems to be searchable only by header info, and as well all know the subject line rarely retains much resemblance to the question inside the message. I'm looking for a nice efficient way to count the number of bits set in an 8-bit register. I _know_ there were some nice pieces out there, but I can't seem to find one. Anybody have one I can use? Thanks. Andy -- http://www.piclist.com hint: The PICList is archived three different ways. See http://www.piclist.com/#archives for details.

Andrew Kunz wrote: >I'm looking for a nice efficient way to count the number of bits set in an 8-bit >register. I _know_ there were some nice pieces out there, but I can't seem to >find one. Same here, I *know* Mr Kiryashov made a wonderful solution about two years ago, but I've lost it. /Morgan -- http://www.piclist.com hint: The PICList is archived three different ways. See http://www.piclist.com/#archives for details.

>I'm looking for a nice efficient way to count the number of bits set in an >8-bit >register. I _know_ there were some nice pieces out there, but I can't seem >to >find one. How about: CBLOCK 0x0C Count Loop_Count ENDC clrf Count movlw 0x08 movwf Loop_Count clrc Loop rrf Number btfsc STATUS, C incf Count decfsz Loop_Count goto Loop Where "Count" holds the number of bits set. I don't know about "efficient," but I'm not sure how to do it faster offhand. or, by brute force: clrf Count btfsc Number, 0 incf Count btfsc Number, 1 incf Count ... etc. This would actually have fewer instruction cycles, but would take up just about twice the program memory. --Andrew _________________________________________________________________ Get your FREE download of MSN Explorer at http://explorer.msn.com -- http://www.piclist.com hint: The PICList is archived three different ways. See http://www.piclist.com/#archives for details.

I remember Dmitry had a **very** fast way of doing this, but I can't find it just now. It's probably several generations of computers ago. However there is a good collection of bit counting methods at:- http://www.dattalo.com/technical/software/pic/picprty.html {Quote hidden}>I'm unable to search the PICLIST.COM archive, and Jeff Keyser's archive seems to >be searchable only by header info, and as well all know the subject line rarely >retains much resemblance to the question inside the message. > >I'm looking for a nice efficient way to count the number of bits set in an 8-bit >register. I _know_ there were some nice pieces out there, but I can't seem to >find one. > >Anybody have one I can use? > >Thanks. > >Andy > Ray Gardiner .....rayKILLspam@spam@dsp.com.au mail from: dsp systems -- http://www.piclist.com hint: The PICList is archived three different ways. See http://www.piclist.com/#archives for details.

On Sat, 16 Dec 2000, Ray Gardiner wrote: > I remember Dmitry had a **very** fast way of doing this, but I can't find it > just now. It's probably several generations of computers ago. > However there is a good collection of bit counting methods at:- > > http://www.dattalo.com/technical/software/pic/picprty.html The ones there are slugs compared to Dmitry's. Scott -- http://www.piclist.com hint: The PICList is archived three different ways. See http://www.piclist.com/#archives for details.

Ok, here is the one I was thinking of. It is archived at http://www.piclist.com/techref/microchip/math/bit/countbits.htm Should have looked on http://www.piclist.com first!.. Dmitry's amazing code follows.... ; Less program memory requiring solution ; 14 clock per convertation but only ; 14 words of program memory is required movfw portX movwf temp_w andlw 0x77 addwf temp_w,f rrf temp_w,f andlw 0x33 addwf temp_w,f rrf temp_w,f andlw 0x11 addwf temp_w,f rrf temp_w,f swapf temp_w,w addwf temp_w,w andlw 0x0F Ray Gardiner rayKILLspamdsp.com.au mail from: dsp systems -- http://www.piclist.com hint: The PICList is archived three different ways. See http://www.piclist.com/#archives for details.

Here's what I found in my archive - no message from Dmitry, though - presumably he had the referenced 13 cycle version... BillW Date: Wed, 22 Jul 1998 12:04:33 +0800 From: Regulus Berdin <.....rberdinKILLspam.....SKYINET.NET> Subject: Re: Bit counting (looking for old challenge emails) To: EraseMEPICLISTspam_OUTTakeThisOuTMITVMA.MIT.EDU Hi to all, > From: Scott Dattalo <sdattalospam_OUTUNIX.SRI.COM> [SNIP] > Thanks for the plug Bill. However, the routines on my web page are by no > means the fastest (as I've been shown). One PICLIST member has an > isochronous bitcount routine that runs in 13 cycles. So unless he wishes > to post it, I guess there's a challenge for someone out there. I took the challenge, here is what I got. BITCOUNT: ;untested RRF Q,W ;Q = abcdefgh MOVWF T ;T = 0abcdefg MOVLW B'01010101' ANDWF Q ;Q = 0b0d0f0h ANDWF T,W ;W = 0a0c0e0g ADDWF Q ;Q = (a+b)(c+d)(e+f)(g+h) RRF Q,W MOVWF T RRF T ;T = (xx)(a+b)(c+d)(e+f) MOVLW B'00110011' ANDWF Q ;Q = (00)(c+d)(00)(g+h) ANDWF T,W ;W = (00)(a+b)(00)(e+f) ADDWF Q ;Q = (a+b+c+d)(e+f+g+h) SWAPF Q,W ;W = (e+f+g+h)(a+b+c+d) ADDWF Q,W ;W = (a+b+c+d+e+f+g+h)(a+b+c+d+e+f+g+h) ANDLW H'0F' ;W = (0000)(a+b+c+d+e+f+g+h) Data is in Q and result is placed in W. The routine is isochronous but 16 cycles. I cannot shave it down to 13 or less :(. I wonder how this piclist member did it or what method/algorithm he used. Reggie -- http://www.piclist.com hint: The PICList is archived three different ways. See http://www.piclist.com/#archives for details.

I just realized that Andy was apparently searching the iversoft archive and thinking that it was the new piclist.com archive. The iversoft archive is at http://www2.iversoft.com/piclist and appears to be down. The new piclist.com archive is at http://www.piclist.com/techref/postbot.asp It is working just fine. You must be a piclist.com member (not just a piclist member) to access it. The code Andy is looking for is at www.piclist.com/techref/microchip/math/bit/countbits.htm and there are many other bit related snippets as well at www.piclist.com/techref/microchip/math/bit/index.htm and a ton of code at www.piclist.com/techref/microchip/routines.htm nicely indexed by subject --- James Newton (PICList Admin #3) @spam@jamesnewtonKILLspampiclist.com 1-619-652-0593 PIC/PICList FAQ: http://www.piclist.com or .org {Original Message removed}