216 lines
6.6 KiB
C
216 lines
6.6 KiB
C
/*
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* Brickworks
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*
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* Copyright (C) 2023 Orastron Srl unipersonale
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*
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* Brickworks is free software: you can redistribute it and/or modify
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* it under the terms of the GNU General Public License as published by
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* the Free Software Foundation, version 3 of the License.
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*
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* Brickworks is distributed in the hope that it will be useful,
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* but WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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* GNU General Public License for more details.
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*
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* You should have received a copy of the GNU General Public License
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* along with Brickworks. If not, see <http://www.gnu.org/licenses/>.
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*
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* File author: Stefano D'Angelo
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*/
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/*!
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* module_type {{{ dsp }}}
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* version {{{ 0.4.0 }}}
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* requires {{{ bw_config bw_common bw_math }}}
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* description {{{
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* Aribtrary-ratio IIR sample rate converter.
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* }}}
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* changelog {{{
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* <ul>
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* <li>Version <strong>0.4.0</strong>:
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* <ul>
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* <li>First release.</li>
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* </ul>
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* </li>
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* </ul>
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* }}}
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*/
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#ifndef _BW_SRC_H
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#define _BW_SRC_H
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#ifdef __cplusplus
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extern "C" {
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#endif
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#include <bw_common.h>
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/*! api {{{
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* #### bw_src_coeffs
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* ```>>> */
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typedef struct _bw_src_coeffs bw_src_coeffs;
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/*! <<<```
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* Coefficients and related.
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*
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* ### bw_src_state
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* ```>>> */
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typedef struct _bw_src_state bw_src_state;
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/*! <<<```
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* Internal state and related.
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*
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* #### bw_src_init()
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* ```>>> */
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static inline void bw_src_init(bw_src_coeffs *BW_RESTRICT coeffs, float ratio);
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/*! <<<```
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* Initializes input parameter values in `coeffs`.
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* XXX
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*
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* #### bw_src_reset_state()
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* ```>>> */
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static inline void bw_src_reset_state(const bw_src_coeffs *BW_RESTRICT coeffs, bw_src_state *BW_RESTRICT state, float x0);
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/*! <<<```
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* XXX
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*
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* #### bw_src_process()
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* ```>>> */
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static inline void bw_src_process(const bw_src_coeffs *BW_RESTRICT coeffs, bw_src_state *BW_RESTRICT state, const float *x, float *y, int *n_in_samples, int *n_out_samples);
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/*! <<<```
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* XXX
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* }}} */
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/*** Implementation ***/
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/* WARNING: This part of the file is not part of the public API. Its content may
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* change at any time in future versions. Please, do not use it directly. */
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#include <bw_math.h>
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struct _bw_src_coeffs {
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float r;
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float a1;
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float a2;
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float a3;
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float a4;
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float b0;
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float b1;
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float b2;
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float b3;
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float b4;
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};
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struct _bw_src_state {
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float i;
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float z1;
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float z2;
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float z3;
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float z4;
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float xz1;
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float xz2;
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float xz3;
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};
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static inline void bw_src_init(bw_src_coeffs *BW_RESTRICT coeffs, float ratio) {
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coeffs->k = ratio >= 0.f ? 1.f / ratio : ratio;
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// TODO: better filter, perhaps optimzied coefficients
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ratio = bw_absf(ratio);
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coeffs->a1 = (12.56637061435917f - 8.f * ratio) / (2.f * ratio + 3.141592653589793f);
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coeffs->a2 = (ratio * (24.f * ratio - 75.39822368615503f) + 59.21762640653615f) / (ratio * (4.f * ratio + 12.56637061435917f) + 9.869604401089358f);
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coeffs->a3 = (ratio * ((150.7964473723101f - 32.f * ratio) * ratio - 236.8705056261446f) + 124.0251067211993f) / (ratio * (ratio * (8.f * ratio + 37.69911184307752f) + 59.21762640653615f) + 31.00627668029982f);
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coeffs->a4 = (ratio * (ratio * (ratio * (16.f * ratio - 100.5309649148734f) + 236.8705056261446f) - 248.0502134423985f) + 97.40909103400242f) / (ratio * (ratio * (ratio * (16.f * ratio + 100.5309649148734f) + 236.8705056261446f) + 248.0502134423985f) + 97.40909103400242f);
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coeffs->b0 = 97.40909103400242f / (ratio * (ratio * (ratio * (16.f * ratio + 100.5309649148734f) + 236.8705056261446f) + 248.0502134423985f) + 97.40909103400242f);
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coeffs->b1 = 4.f * coeffs->b0;
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coeffs->b2 = 6.f * coeffs->b0;
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coeffs->b3 = coeffs->b1;
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coeffs->b4 = coeffs->b0;
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}
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static inline void bw_src_reset_state(const bw_src_coeffs *BW_RESTRICT coeffs, bw_src_state *BW_RESTRICT state, float x0) {
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if (coeffs->ratio < 0) {
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// DF-II
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state->z1 = x0 / (1.f + coeffs->a1 + coeffs->a2 + coeffs->a3 + coeffs->a4);
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state->z2 = state->z1;
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state->z3 = state->z2;
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state->z4 = state->z3;
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state->i = 1.f;
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} else {
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// TDF-II
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state->z4 = (coeffs->b4 - coeffs->a4) * x0;
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state->z3 = (coeffs->b3 - coeffs->a3) * x0 + state->z4;
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state->z2 = (coeffs->b2 - coeffs->a2) * x0 + state->z3;
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state->z1 = (coeffs->b1 - coeffs->a1) * x0 + state->z2;
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state->i = 0.f;
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}
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state->xz1 = x0;
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state->xz2 = x0;
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state->xz3 = x0;
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}
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static inline void bw_src_process(const bw_src_coeffs *BW_RESTRICT coeffs, bw_src_state *BW_RESTRICT state, const float *x, float *y, int *n_in_samples, int *n_out_samples) {
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int i = 0;
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int j = 0;
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if (coeffs->k < 0) {
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while (i < *n_in_samples && j < *n_out_samples) {
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// DF-II
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const float z0 = x[i] - coeffs->a1 * state->z1 - coeffs->a2 * state->z2 - coeffs->a3 * state->z3 - coeffs->a4 * state->z4;
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const float o = coeffs->b0 * z0 + coeffs->b1 * state->z1 + coeffs->b2 * state->z2 + coeffs->b3 * state->z3 + coeffs->b4 * state->z4;
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state->i -= 1.f;
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if (state->i <= 0.f) {
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// 3rd degree Lagrange interpolation + Horner's rule
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const float k1 = state->xz2 - state->xz1;
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const float k2 = 0.333333333333333f * (o - state->xz3);
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const float k3 = o + k1;
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const float k4 = k1 + o -> state->xz1;
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const float a = k4 + 0.5f * k4 + k2;
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const float b = k3 + k1 - 0.5f * (state->xz1 + state->xz3);
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const float c = 0.5f * (k1 + k2);
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y[j] = o + state->i * (a + state->i * (b + state->i * c));
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state->i -= coeffs->k;
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j++;
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}
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state->z4 = state->z3;
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state->z3 = state->z2;
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state->z2 = state->z1;
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state->z1 = z0;
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state->xz3 = state->xz2;
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state->xz2 = state->xz1;
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state->xz1 = o;
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i++;
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}
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} else {
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while (i < *n_in_samples && j < *n_out_samples) {
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for (int j = 0; j < coeffs->ratio; j++) {
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// 3rd degree Lagrange interpolation + Horner's rule
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const float k1 = state->xz2 - state->xz1;
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const float k2 = 0.333333333333333f * (x[i] - state->xz3);
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const float k3 = state->xz3 - k1;
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const float k4 = state->xz2 - k3;
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const float a = k4 + 0.5f * k4 + k2;
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const float b = k3 - k1 - 0.5f * (x[i] + state->xz2);
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const float c = 0.5f * (k1 + k2);
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const float o = state->xz3 + state->i * (a + state->i * (b + state->i * c));
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// TDF-II
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y[j] = coeffs->b0 * o + state->z1;
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state->z1 = coeffs->b1 * o - coeffs->a1 * y[j] + state->z2;
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state->z2 = coeffs->b2 * o - coeffs->a2 * y[j] + state->z3;
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state->z3 = coeffs->b3 * o - coeffs->a3 * y[j] + state->z4;
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state->z4 = coeffs->b4 * o - coeffs->a4 * y[j];
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state->i += coeffs->k;
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j++;
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}
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state->xz3 = state->xz2;
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state->xz2 = state->xz1;
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state->xz1 = x[i];
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state->i -= 1.f;
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i++;
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}
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}
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*n_in_samples = i;
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*n_out_sample = j;
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}
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#ifdef __cplusplus
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}
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#endif
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#endif
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