FIR滤波器的C语言程序

#include

#define length 256

int input[length],output[length];

static int filter(int xin[],int xout[],int n, int h[]);

static void dataIO(void);

static int h[37]={ -78,-152,-210,-173,18,355,737,983,903,413,-374,
-1139,-1443,-910,582,2792,5154,6963,7640,6963,5154,2792,582,-910,
-1443,-1139,-374,413,903,983,737,355,18,-173,-210,-152,-78};

static int x1[length+37];

static int filter(int indata[],int outdata[],int n,int h[])
{
int i,j;
long sum;

for(i=0;i x1[n+i-1]=indata[i];

for(i=0;i<(n-1);i++)
x1[n-i-2]=indata[length-i-1];

for(i=0;i {
sum=0;
for(j=0;j sum+=(long)h[j]*x1[i-j+n-1];
outdata[i]=sum>>15;
}
return 1;
}
void main()
{
while(1)
{
dataIO();
filter(input,output,19,h);
}
}
static void dataIO()
{

return;
}
谁能告诉我程序第二行的length是啥意思？是我这组需要滤波数据的个数么？？

length==256

short h[], short y[]) { int i, j, sum; for (j = 0; j < 100; j++) { sum = 0; for (i = 0; i < 32; i++) sum += x[i+j] * h[i]; y[j] = sum >> 15; } } 2 void fir(short x[], short h[], short y[]) { int i, j, sum0, sum1; short x0,x1,h0,h1; for (j = 0; j < 100; j+=2) { sum0 = 0; sum1 = 0; x0 = x[j]; for (i = 0; i < 32; i+=2){ x1 = x[j+i+1]; h0 = h[i]; sum0 += x0 * h0; sum1 += x1 * h0; x0 = x[j+i+2]; h1 = h[i+1]; sum0 += x1 * h1; sum1 += x0 * h1; } y[j] = sum0 >> 15; y[j+1] = sum1 >> 15; } } 3 void fir(short x[], short h[], short y[]) { int i, j, sum0, sum1; short x0,x1,x2,x3,x4,x5,x6,x7,h0,h1,h2,h3,h4,h5,h6,h7; for (j = 0; j < 100; j+=2) { sum0 = 0; sum1 = 0; x0 = x[j]; for (i = 0; i < 32; i+=8){ x1 = x[j+i+1]; h0 = h[i]; sum0 += x0 * h0; sum1 += x1 * h0; x2 = x[j+i+2]; h1 = h[i+1]; sum0 += x1 * h1; sum1 += x2 * h1; x3 = x[j+i+3]; h2 = h[i+2]; sum0 += x2 * h2; sum1 += x3 * h2; x4 = x[j+i+4]; h3 = h[i+3]; sum0 += x3 * h3; sum1 += x4 * h3; x5 = x[j+i+5]; h4 = h[i+4]; sum0 += x4 * h4; sum1 += x5 * h4; x6 = x[j+i+6]; h5 = h[i+5]; sum0 += x5 * h5; sum1 += x6 * h5; x7 = x[j+i+7]; h6 = h[i+6]; sum0 += x6 * h6; sum1 += x7 * h6; x0 = x[j+i+8]; h7 = h[i+7]; sum0 += x7 * h7; sum1 += x0 * h7; } y[j] = sum0 >> 15; y[j+1] = sum1 >> 15; } }