/***************************************************************************
 *   Copyright (C) 2020 - 2025 by Federico Amedeo Izzo IU2NUO,             *
 *                                Niccolò Izzo IU2KIN,                     *
 *                                Silvano Seva IU2KWO,                     *
 *                                Frederik Saraci IU2NRO                   *
 *                                                                         *
 *   This program is free software; you can redistribute it and/or modify  *
 *   it under the terms of the GNU General Public License as published by  *
 *   the Free Software Foundation; either version 3 of the License, or     *
 *   (at your option) any later version.                                   *
 *                                                                         *
 *   This program is distributed in the hope that it will be useful,       *
 *   but WITHOUT ANY WARRANTY; without even the implied warranty of        *
 *   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the         *
 *   GNU General Public License for more details.                          *
 *                                                                         *
 *   You should have received a copy of the GNU General Public License     *
 *   along with this program; if not, see <http://www.gnu.org/licenses/>   *
 ***************************************************************************/

#include <dsp.h>

int16_t dsp_dcBlockFilter(struct dcBlock *dcb, int16_t sample)
{
    /*
     * Implementation of a fixed-point DC block filter with noise shaping,
     * ensuring zero DC component at the output.
     * Filter pole set at 0.995
     *
     * Code adapted from https://dspguru.com/dsp/tricks/fixed-point-dc-blocking-filter-with-noise-shaping/
     */
    dcb->accum -= dcb->prevIn;
    dcb->prevIn = static_cast<int32_t>(sample) << 15;
    dcb->accum += dcb->prevIn;
    dcb->accum -= 164 * dcb->prevOut; // 32768.0 * (1.0 - pole)
    dcb->prevOut = dcb->accum >> 15;

    return static_cast<int16_t>(dcb->prevOut);
}