p_firdec.c

#include <pal.h>

/**
 * Computes a decimating FIR filter (direct-form) on input data 'x' using
 * coefficient stored in 'h' and places result in 'r'. This function
 * retains the address of the delay filter memory containing the previous
 * delayed values to allow consecutive processing of blocks.
 *
 * @param x     Pointer to input vector of 'n' elements
 *
 * @param h     Pointer to filter coefficients.
 *
 * @param r     Pointer to result vector of size nx/d.
 *
 * @param nx    The number of input samples
 *
 * @param nh    The number of coefficients of the filter.
 *
 * @param df    Decimation factor. (1 output sample per 'd' input samples)
 *
 * @return      None
 *
 */
void p_firdec_f32(const float *x, const float *h, float *r,
                  int nx, int nh, int df)
{
	int t;
	int i;
	for (t = 0; t < nh; ++t)
	{
	 	r[t] = 0;
		for (i = 0; i <= t && t * df < nx; ++i) 
			r[t] += h[i] * x[t * df - i];
	}

	for (t = nh; t < nx; ++t)
	{
		r[t] = 0;
		for (i = 0; i < nh && t * df < nx; ++i)
			r[t] += h[i] * x[t * df - i];
	}
}