/*********************************************************************************
Module Name     : .asm
Label Name      : 


   Version     Date          Author        Comments
    
   1.0         15/02/2007     HuBo      	Original 

Description     : 	This function performs FIR filter operation on given input.

Prototype       :	void	_updatafilt(short *h, short *pSig, short send)

return 			:  	None                  
          
Performance		:       
*******************************************************************************/
.section L1_code;
.global   _updatefilt;
.align 8;

/*h(k)=(h(k)<<16+(r(n)<<16)*s(n-k))>>16*/
_updatefilt:
	LINK 0x30 ;
	[ -- SP ] = (R7:4);
	I0 = R0;
	I2 = R0;
	I1 = R1;
	P2 = 256;
	R0 = [I0++];				//load h[0] and increase I0;
	R7 = 0x7fff;
	M0 = 4;
	M1 = 2;
	
	R1 = I1;					/*store address of s_register[256+i]*/
	R3 = 0x00000003;
	R3 = R1 & R3;
	CC = R3 == 0;
	if !CC JUMP	offset_1;

offset_0:	
	/*initiate a0, a1 and R3, a0 and a1 left ashift 15*/
	R1.L = W[I1--]; 
	LSETUP(update_coef_beg_0, update_coef_end_0) LC0 = P2>>1;	
update_coef_beg_0:	A0 = R0.L * R7.L, A1 = R0.H * R7.L || R1.H = W[I1--] ;	/*a0 and a1 left shift 16 bit*/

/*the high half of the result is extracted and stored in the 16-bit destination registers */
					R0.L = (A0 += R2.L * R1.L) , R0.H = (A1 += R2.L * R1.H) || R1.L = W[I1--];
update_coef_end_0:	MNOP ||[I2++M0] = R0 || R0 = [I0++M0];//store R0 and increase I0;
	jump update_end;

offset_1:/*the address of s_register[256+i] isn't aligned by 4-byte */
	
	I1 -= M1;
	LSETUP(update_coef_beg_1, update_coef_end_1) LC0 = P2>>1;
update_coef_beg_1:	A0 = R0.L * R7.L, A1 = R0.H * R7.L || R1 = [I1--] ;/*a0 and a1 left shift 16 bit*/

/*the high half of the result is extracted and stored in the 16-bit destination registers */
					
					R0.L = (A0 += R2.L * R1.L), R0.H = (A1 += R2.L * R1.H);// || R1.L = W[I1--];
update_coef_end_1:	MNOP || [I2++M0]=R0 || R0 = [I0++M0];//store R0 and increase I0;

update_end:
	(R7:4) = [ SP++ ] ;			//Load register R7-R4
	UNLINK;
	RTS;
_updatefilt.end: