please dont rip this site

PIC Microcontoller Math Method

Complex number magnitude calculation

Nikolai Golovchenko says:

	cblock 0x20
	Temp, Counter
	ReH, ReL, ImH, ImL
	RekH, RekL, ImkH, ImkL
	endc

#define XX 22520
#define YY 1
	movlw low(XX)
	movwf ReL
	movlw high(XX)
	movwf ReH
	movlw low(YY)
	movwf ImL
	movlw high(YY)
	movwf ImH
again
	call Magnitude16
stop
	nop
	incf ReL, f
	skpnz
	 incf ReH, f
	movf ImL, f
	skpnz
	 decf ImH, f
	decf ImL, f
	goto again


;***********************************************
; Complex number magnitude calculation
; using CORDIC algorithm described at
; www.dspguru.com\info\faqs\cordic.htm
;
; Input:
;  ReH:ReL, ImH:ImL - complex number (16 bit signed)
;
; Output:
;  ReH:ReL - magnitude (16 bit unsigned)
;  ImH:ImL - garbage
;
; Temporaries:
;  RekH:RekL - Re multipled by k (k=2^-L, L=0,1,2,...15)
;  Counter - loop counter
;  Temp
;
; Instructions: 147
; Execution time(worst case including return):
;  18+18+15*(8+2+20+4+7.5*9)+60 ~= 1600 instruction cycles

; Notes:
;  1) Precision is 0.028%, depends on how exact
;  the division by CORDIC gain is implemented:
;	(0.60725293510314)
;	a) 1/2+1/8-1/64-1/512 -> 0.028%
;	b) 1/2+1/8-1/64-1/512-1/4096 -> 0.012384%
;	c) 1/2+1/8-1/64-1/512-1/4096+1/16384 -> 0.002333%
;  2) Range of input data should be restricted so
;  that M=sqrt(Re*Re+Im*Im) is less than 65536*0.60725293510314~=39760
;  to prevent overflow in magnitude during calculation
;  3) To reduce execution time, the number of loops can be
;  reduced to 8. The angle after rotation the initial
;  vector 8 times is less then 0.22381 deg, which is good
;  enough precision. Besides, the gain at 8 rotations is smaller
;  and closer to the approximated gain, which is used in this code.
;  Reduced execution time will be ~800 cycles!
;
; 6 Aug 2000 by Nikolai Golovchenko
;***********************************************
Magnitude16
;Find absolute value of the vector components
	btfss ReH, 7		;Re = abs(Re)
	 goto Magnitude16a
	comf ReL, f
	comf ReH, f
	incf ReL, f
	skpnz
	 incf ReH, f
Magnitude16a
	btfss ImH, 7		;Im = abs(Im)
	 goto Magnitude16b
	comf ImL, f
	comf ImH, f
	incf ImL, f
	skpnz
	 incf ImH, f
Magnitude16b
;Test imaginary part for zero and if yes, quit
	movf ImL, w
	iorwf ImH, w
	skpnz
	 return			;quit if zero imaginary part
;Perform first iteration
	movf ImL, w		;Imk = Im
	movwf ImkL
	movf ImH, w
	movwf ImkH
	
	movf ReL, w		;Im' = Im - Re
	subwf ImL, f
	movf ReH, w
	skpc
	 incfsz ReH, w
	  subwf ImH, f

	movf ImkL, w		;Re' = Re + Im = Re + Imk
	addwf ReL, f
	movf ImkH, w
	skpnc
	 incfsz ImkH, w
	  addwf ReH, f
;Begin loop
	movlw	1
	movwf Counter
Magnitude16loop
;load scaled values
	movf ImL, w		;Imk = Im
	movwf ImkL
	movf ImH, w
	movwf ImkH
	movf ReL, w		;Rek = Re
	movwf RekL
	movf ReH, w
	movwf RekH
;scale them (1 to 15 right shifts)
	movf Counter, w		;load counter value to Temp
	movwf Temp
Magnitude16loop2
	clrc			;unsigned right shift for Rek
	rrf RekH, f
	rrf RekL, f
	rlf ImkH, w		;signed right shift for Imk
	rrf ImkH, f
	rrf ImkL, f
	decfsz Temp, f
	 goto Magnitude16loop2
;update current values
	movf ImkL, w	
	btfsc ImH, 7		;if Im < 0 add a phase, if Im >= 0 substract a phase
	 goto Magnitude16AddPhase
;substract a phase
	addwf ReL, f		;Re' = Re + Imk
	movf ImkH, w
	skpnc
	 incfsz ImkH, w
	  addwf ReH, f

	movf RekL, w		;Im' = Im - Rek
	subwf ImL, f
	movf RekH, w
	skpc
	 incfsz RekH, w
	  subwf ImH, f

	goto Magnitude16loopend
Magnitude16AddPhase
;add a phase
	skpnc			;correct Imk, because shifts of negative
	 incfsz ImkL, w 	;values like (-1 >> 1 = -1) can
	decf ImkH, f		;accumulate error. With this correction,
	incf ImkH, f		;shifts of negative values will work like
				;shifts of positive values (i.e. round to zero)
				
	subwf ReL, f		;Re' = Re - Imk
	movf ImkH, w
	skpc
	 incfsz ImkH, w
	  subwf ReH, f

	movf RekL, w		;Im' = Im + Rek
	addwf ImL, f
	movf RekH, w
	skpnc
	 incfsz RekH, w
	  addwf ImH, f
Magnitude16loopend
	incf Counter, f
	btfss Counter, 4	;repeat untill counter reaches 16
;or uncomment this for better performance
;	btfss Counter, 3	;repeat untill counter reaches 8
	 goto Magnitude16loop

;Optional:
;Divide result by 1.64676025786545 (CORDIC gain)
;or multiply by 0.60725293510314 = 1/2+1/8-1/64-1/512 - 0.028%
	movf	ReH, w
	movwf	RekH
	movf	ReL, w
	movwf	RekL
	clrc
	rrf	ReH, f
	rrf	ReL, f
	clrc
	rrf	ReH, f
	rrf	ReL, f
	clrc
	rrf	ReH, f
	rrf	ReL, f
	comf	ReL, f
	comf	ReH, f
	incf	ReL, f
	skpnz
	incf	ReH, f
	clrf	Temp
	btfsc	ReH, 7
	comf	Temp, f
	subwf	ReL, f
	movf	RekH, w
	skpc
	incfsz	RekH, w
	subwf	ReH, f
	skpc
	 decf Temp, f
	rrf	Temp, f
	rrf	ReH, f
	rrf	ReL, f
	rrf	Temp, f
	rrf	ReH, f
	rrf	ReL, f
	rlf	ReH, w
	rrf	ReH, f
	rrf	ReL, f
	movf	RekL, w
	addwf	ReL, f
	movf	RekH, w
	skpnc
	incfsz	RekH, w
	addwf	ReH, f
	clrc
	rrf	ReH, f
	rrf	ReL, f
	clrc
	rrf	ReH, f
	rrf	ReL, f
	movf	RekL, w
	addwf	ReL, f
	movf	RekH, w
	skpnc
	incfsz	RekH, w
	addwf	ReH, f
	rrf	ReH, f
	rrf	ReL, f

;Done!
	return
;***********************************************






Comments:


file: /Techref/microchip/math/vector/mag-ng.htm, 5KB, , updated: 2007/2/13 13:43, local time: 2024/3/19 06:59,
TOP NEW HELP FIND: 
3.85.63.190:LOG IN

 ©2024 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! / MAKE!

<A HREF="http://www.piclist.com/techref/microchip/math/vector/mag-ng.htm"> PIC Microcontoller Math Method </A>

After you find an appropriate page, you are invited to your to this massmind site! (posts will be visible only to you before review) Just type a nice message (short messages are blocked as spam) in the box and press the Post button. (HTML welcomed, but not the <A tag: Instead, use the link box to link to another page. 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: 
Attn spammers: All posts are reviewed before being made visible to anyone other than the poster.
Did you find what you needed?

  PICList 2024 contributors:
o List host: MIT, Site host massmind.org, Top posters @none found
- 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!

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

  .