please dont rip this site

PIC Microcontoller Basic Math Multiplication Methods

Archive:

4x4 bit multiply 


; 4x4 bit multiply
; result in W
; by  John Payson
       movlw   0
       bcf     C
       btfss   n1,0
       addwf   n2,w
       rlf     n2,f
       btfss   n1,1
       addwf   n2,w
       rlf     n2,f
       btfss   n1,2
       addwf   n2,w
       rlf     n2,f
       btfss   n1,3
       addwf   n2,w
       rlf     n2,f
       swapf   n2,f
; 15 cycles, putting the result in W and
; leaving n1 and n2 untouched at the end.
; Striking the requirement that n2 be untouched would save the
; last two cycles.
; Note that if n1<=15 and n1*n2<=255 this routine will ; produce a correct result even if n2>15;
; the value in n2 will be trashed in such a case, though.


; 4x4 bit multiply
; by  John Payson
; result in n2...
       swapf   n1,w    ; Assume top 4 bits zero
       btfss   n2,0
       addwf   n2,f
       rrf     n2,f

If we have Cy=1 before entering this code fragment and we skip first addition we'll got error. 


       btfss   n2,0
       addwf   n2,f
       rrf     n2,f
       btfss   n2,0
       addwf   n2,f
       rrf     n2,f
       btfss   n2,0
       addwf   n2,f
       rrf     n2,f
; 13 cycles, leaving the result in n2.
; This one won't work if either factor is oversized.




; 4x4 bit multiply
; by Ray Gardiner
       ;  X*Y ; result left in W
       ;  X and Y are 4 bits
       ;
       ;
       CLRW            ; Clear Result
       CLRC            ; Clear Carry for RLF later                     ;
       BTFSC   Y,0     ; ?*1
       ADDWF   X,W     ; W = ?X
       RLF     X,F     ; X = 2X
                       ;
       BTFSC   Y,1     ; ?*2
       ADDWF   X,W     ; W = ?X + ?2X
       RLF     X,F     ; W = 4X

       BTFSC   Y,2     ; ?*4
       ADDWF   X,W     ; W = ?X + ?2X + ?4X
       RLF     X,F     ; W = 8X

       BTFSC   Y,3     ; ?*8
       ADDWF   X,W     ; ?X + ?2X + ?4X + ?8X
       ;;;;;;;;;;;;;;;;;;;;;;;;;

       13 cycles result in W  13 bytes of code space


Looking back, I now realise that is what John Payson has already
posted. Albeit in a different form. Sigh(!)




;       4 X 4 multiplication
; by Dmitry Kiryashov
       movfw   x       ;0000abcd
       addwf   x,F
       btfss   y,0     ;0000efgh
       movlw   0
       btfsc   y,1
       addwf   x,W
       rlf     x,F
       btfsc   y,2
       addwf   x,W
       rlf     x,F
       btfsc   y,3
       addwf   x,W     ;result in W
;       12 clocks/words

Interested:

See:

32-bit signed integer math routines. add, subtract, multiply, divide, round, sqrt, bin2dec, dec2bin. By Peter Hemsley. +

Questions:

Comments:

file: /techref/microchip/math/mul/index.htm, 10KB, , updated: 2008/9/1 12:50, local time: 2008/10/11 19:12,
TOP NEW HELP FIND: 
38.103.63.61:LOG IN
©2008 PLEASE DON'T RIP! DO: LINK / DIGG! / MAKE!
 ©2008 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?
Please DO link to this page! Digg it!
<A HREF="http://piclist.com/techref/microchip/math/mul/index.htm"> PIC Microcontoller Basic Math Multiplication Methods</A>
After you find an appropriate page, you are invited to your to this massmind site! (posts will be reviewed) Just type in the box and press the Post button. (HTML welcomed!): A tutorial is available Members can login to post directly, become page editors, and be credited for their posts.


Link? Put it here: 
if you want a response, please enter your email address: 
Did you find what you needed?
  PICList 2008 contributors:
o List host: MIT, Site host massmind.org, Top posters @20081011 Apptech, Jinx, Xiaofan Chen, olin piclist, Vitaliy, Alan B. Pearce, William \Chops\ Westfield, JonnyMac, Tamas Rudnai, Gerhard Fiedler,
* 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: Shultz Electronics, Timothy Weber, on-going support is MOST appreciated!
* Contributors: Richard Seriani, Sr.
  'What can I do?' - SiCKO

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

  .