Dmitry Kiryashov [zews at AHA.RU] says:
...to convert byte mask back into number. I suggest that somebody else probably has successfully researched this before. This is what I've discovered... It takes 12 clocks/words; W before -> W after ; abcdefgh -> 00000ABC ; 10000000 -> 7 = 4+2+1 ; 01000000 -> 6 = 4+2+0 ; 00100000 -> 5 = 4+0+1 ; 00010000 -> 4 = 4+0+0 ; 00001000 -> 3 = 0+2+1 ; 00000100 -> 2 = 0+2+0 ; 00000010 -> 1 = 0+0+1 ; 00000001 -> 0 = 0+0+0 movwf temp ;save abcdefgh swapf temp,W ;efghabcd xorwf temp,F ;........ andlw 0xF ;0000abcd skpz movlw 4 ;load A=0/4 btfss temp,3 btfsc temp,2 iorlw 2 ;add B=0/2 btfss temp,3 btfsc temp,1 iorlw 1 ;add C=0/1 ;W holds 7..0 of result
Marc [marc at AARGH.FRANKEN.DE] says:
You can make it a table-read, and fill the gaps with other sub functions. Under the presumption that you can make use of any area of 3+ words in size, this method uses 6 cycles (incl call/ret) and 11 words.addwf pc,f (1 wasted word) retlw 0 retlw 1 (1 wasted word) retlw 2 (3 spare words) retlw 3 (7 spare words) retlw 4 (15 spare words) retlw 5 ...
+;Gonzalo Barco ;A looped approach (a bit smaller and lot slower) ;In case you are sure there's at least one bit set you can loose the first bsf COMPACT4BIT MACRO FILE ;Returns bit 3 set on error (no bits set) local loop, tail bsf STATUS, C ;To be sure we don't looooooooooooop forever clrw ;Clear counter loop: rrf FILE, F ;Send bits off the edge... btfsc STATUS, C ;...on to STATUS, C goto tail ;If we hit the bit... stop addlw 1 ;Otherwise add to the counter... goto loop ;...and keep looping tail: movwf FILE ;Overwrite source with result ENDM
|file: /Techref/microchip/math/bit/whatbit.htm, 3KB, , updated: 2009/4/16 14:48, local time: 2018/3/22 20:48,
|©2018 These pages are served without commercial sponsorship. (No popup ads, etc...).Bandwidth abuse increases hosting cost forcing sponsorship or shutdown. This server aggressively defends against automated copying for any reason including offline viewing, duplication, etc... Please respect this requirement and DO NOT RIP THIS SITE. Questions?|
<A HREF="http://www.piclist.com/techref/microchip/math/bit/whatbit.htm"> PIC Microcontoller Bit Math Method </A>
|Did you find what you needed?|
PICList 2018 contributors:
o List host: MIT, Site host massmind.org, Top posters @20180322 RussellMc, Isaac M. Bavaresco, Sean Breheny, Van Horn, David, Neil, alan.b.pearce, Bob Blick, David C Brown, John Gardner, Brent Brown,
* Page Editors: James Newton, David Cary, and YOU!
* Roman Black of Black Robotics donates from sales of Linistep stepper controller kits.
* Ashley Roll of Digital Nemesis donates from sales of RCL-1 RS232 to TTL converters.
* Monthly Subscribers: Gregg Rew. on-going support is MOST appreciated!
* Contributors: Richard Seriani, Sr.
Welcome to www.piclist.com!