fir.c

C语言DSPFFT算法

#include "fir.h"

#define N 48
#define N2 24

float shifter[N];	//the shift registers

float coefficient1[] = 
		{0.0001454484984531, -0.001861906583965, -0.004237972639138, -0.007619623174828,
		-0.01101687204104, -0.0130983131512, -0.01247543991195, -0.00829899182837,
		-0.0008481734259407, 0.008172132934125, 0.01586052144191, 0.0189324366954,
	 	0.01494241097688, 0.003527321898082, -0.0128310339597, -0.02893726515597,
   		-0.03804005078092, -0.03379048931743, -0.01243833306669,  0.02548243007452,
    	0.07462839331434, 0.1257854928957, 0.1681154506852, 0.1920693684775};

float coefficient2[] = {
   0.007892214281376, 0.001700541806004,0.0007270681388075,-0.001082649543886,
  -0.003583478321026,-0.006430348602174, -0.00912652004365, -0.01105549148905,
   -0.01159847831035, -0.01021782078312, -0.00658544236293,-0.0006722672874986,
   0.007142445809834,  0.01605787734213,  0.02492050445769,  0.03220436016868,
    0.03618649333017,  0.03502915902538,  0.02676627807414,  0.00912441892671,
   -0.02146971320706, -0.07340651140725,  -0.1780343231821,  -0.6249128084001};

float prefilter(float data, float coefficient[],int whichFilter)
{
	static int pointer=-1;

	int i,j,k;
	float temp;
	temp=0.0;
	
	pointer=(pointer+1)%N;
	shifter[pointer] = data;
	if(whichFilter == 1)
	{
		for(i=0;i<N2;i++)
		{
			j=(pointer+i)%N;
			k=(pointer-i-1+N)%N;
			temp+=(shifter[j]+shifter[k])*coefficient[i];
		}
	}
	else if(whichFilter == 2)
	{
		for(i=0;i<N2;i++)
		{
			j=(pointer+i)%N;
			k=(pointer-i-1+N)%N;
			temp+=(shifter[j]-shifter[k])*coefficient[i];
		}
	}
	return temp;
}

void initial_filter(void)
{
	int i;
	for(i=0;i<N;i++)
	{
		shifter[i]=0;
	}
}