dsps_firmr_s16_ansi.c File Reference

#include "dsps_fir.h"
#include "dsp_common.h"
#include "dsp_tests.h"

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Functions
int32_t	dsps_firmr_s16_ansi (fir_s16_t *fir, const int16_t *input, int16_t *output, int32_t input_len)
	16 bit signed fixed point multi-rate FIR filter

Function Documentation

dsps_firmr_s16_ansi()

int32_t dsps_firmr_s16_ansi	(	fir_s16_t *	fir,
		const int16_t *	input,
		int16_t *	output,
		int32_t	input_len )

16 bit signed fixed point multi-rate FIR filter

Function implements FIR filter with decimation The extension (_ansi) uses ANSI C and could be compiled and run on any platform. The extension (_ae32) is optimized for ESP32 chip.

Parameters

fir	pointer to fir filter structure, that must be initialized before
input	input array
output	array with the result of the FIR filter
input_len	length of the intput array

Returns

: function returns the number of samples stored in the output array depends on the previous state value could be [0..len*intepr/decimation]

Definition at line 11 of file dsps_firmr_s16_ansi.c.

{
    int32_t result = 0;
    long long rounding = 0;
    const int32_t final_shift = fir->shift - 15;
    rounding = (long long)(fir->rounding_val);
 
    if (fir->shift >= 0) {
        rounding = (rounding >> fir->shift) & 0xFFFFFFFFFF;         // 40-bit mask
    } else {
        rounding = (rounding << (-fir->shift)) & 0xFFFFFFFFFF;      // 40-bit mask
    }
 
    int32_t m = fir->start_pos;
 
    for (int i = 0; i < input_len; i++) {
        fir->delay[fir->pos] = input[i];
 
        for (m = fir->start_pos; m < fir->interp; m += fir->decim) {
            long long acc = rounding;
            int coeff_pos = 0;
            for (int n = fir->pos; n < fir->delay_size; n++) {
                acc += (int32_t)fir->delay[n] * (int32_t)fir->coeffs[coeff_pos++ * fir->interp + m];
            }
            for (int n = 0; n < fir->pos; n++) {
                acc += (int32_t)fir->delay[n] * (int32_t)fir->coeffs[coeff_pos++ * fir->interp + m];
            }
 
            if (final_shift > 0) {
                output[result++] = (int16_t)(acc << final_shift);
            } else {
                output[result++] = (int16_t)(acc >> (-final_shift));
            }
        }
        fir->start_pos = m - fir->interp;
 
        fir->pos--;
        if (fir->pos < 0) {
            fir->pos = fir->delay_size - 1;
        }
    }
 
    return result;
}

References fir_s16_s::coeffs, fir_s16_s::decim, fir_s16_s::delay, fir_s16_s::delay_size, fir_s16_s::interp, m, n, fir_s16_s::pos, fir_s16_s::rounding_val, fir_s16_s::shift, and fir_s16_s::start_pos.