/*---------------------------------------------------------
 *
 * Finite Impulse Response (FIR) Filter (Uniprocessor)
 *
 */

#include<stdlib.h>
#include"fir.h"
#include<cassert.h>


// convention: weights[0] is multiplied by least delayed input
short int weights[TAPS], inputVector[TAPS];
int vectorStart=0;

long int fir(short int in)
{
    int j;
    long int sum = 0;           // 40 bits would be preferred

 // keep vectorStart bounded, code works for all % implementations
vectorStart=(vectorStart+TAPS-1)%TAPS;
    inputVector[vectorStart] = in;
    for (j = 0; j < TAPS; j++) // inner product of weights
        sum += weights[j] * inputVector[(j+vectorStart)%TAPS];

    return (sum);
}