Efficient Fixed-Point Trigonometry For PIC16F

[mister_e]

looking at the asm... i'm aware that my asm skills sucks, but, i don't understand why they used the line in red...

ATAN
	banksel	   _Z_H				; Z_H & Z_L is loaded with 0x0000
	movlw		0x00				; Y & X is the input
	movwf		_Z_H				; X(i+1)	=	Xi - Yi*_Di*2^-i
	movlw		0x00				; Y(I+1)	=	Yi + Xi*_Di*2^-i
	movwf		_Z_L				; Z(i+1)	=	Zi - _Di*ATAN(2^-i)
	banksel	   _Di					; _Di		=	1 if Yi < 0 ELSE _Di	=	0
	bsf		      RV					; Set Vectoring Mode
	goto		CORDIC_Alg		

SINCOS
	banksel	   _Y_L				; Z_H & Z_L is the input
	movlw		0x00				; Y_H & Y_L is loaded with 0x0000	
	movwf		_Y_L				; X_H & X_L is loaded with 6070 (1/An constant)
	movlw		0x00			
	movwf		_Y_H			
	movlw		LOW .6070	
	movwf		_X_L				; X(i+1)	=	Xi - Yi*_Di*2^-i
	movlw		HIGH .6070		; Y(I+1)	=	Yi + Xi*_Di*2^-i
	movwf		_X_H				; Z(i+1)	=	Zi - _Di*ATAN(2^-i)
	banksel	   _Di					; _Di		=	0 if Zi < 0 ELSE _Di	=	1
	bcf		      RV					; Set Rotational Mode

w already hold 0x00 and they reload it again for the next MOVWF? BTW i would use CLRF instead... no big deal, it remove 4 instructions... long run, it may decrease a little bit the calculation latency. OK OK no big improvement, but... i couldn't resist. maybe i'll find something else?

so, once modified, the above code section should look like...

ATAN
	CHK?RP	_Z_H		; Z_H & Z_L is loaded with 0x0000
				; Y & X is the input
	clrf	_Z_H		; X(i+1) = Xi - Yi*_Di*2^-i
				; Y(I+1) = Yi + Xi*_Di*2^-i
	clrf	_Z_L		; Z(i+1) = Zi - _Di*ATAN(2^-i)
	CHK?RP	_Di		; _Di	 = 1 if Yi < 0 ELSE _Di	= 0
	bsf	RV		; Set Vectoring Mode
	goto	CORDIC_Alg		

SINCOS
	CHK?RP	_Y_L		; Z_H & Z_L is the input
				; Y_H & Y_L is loaded with 0x0000	
	clrf	_Y_L		; X_H & X_L is loaded with 6070 (1/An constant)
				
	clrf	_Y_H	
	movlw	LOW .6070
	movwf	_X_L		; X(i+1) = Xi - Yi*_Di*2^-i
	movlw	HIGH .6070	; Y(I+1) = Yi + Xi*_Di*2^-i
	movwf	_X_H		; Z(i+1) = Zi - _Di*ATAN(2^-i)
	CHK?RP	_Di		; _Di	 = 0 if Zi < 0 ELSE _Di	= 1
	bcf	RV		; Set Rotational Mode

But yeah, i think we're not at the optimization stage yet