82 lines
2.0 KiB
C
82 lines
2.0 KiB
C
/* Clipper implementation, based on code by Jonathan Olds
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*
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* (C) 2017 by Andreas Eversberg <jolly@eversberg.eu>
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* All Rights Reserved
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*
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* This program 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, either version 3 of the License, or
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* (at your option) any later version.
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*
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* This program 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 this program. If not, see <http://www.gnu.org/licenses/>.
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*/
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#include <stdio.h>
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#include <math.h>
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#include <stdint.h>
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#include <stdlib.h>
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#include "../libsample/sample.h"
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#include "clipper.h"
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static double clipper_lut[6000];
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static double clipper_point = NAN;
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void clipper_init(double point)
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{
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double a;
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int i;
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if (point > 0.99)
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point = 0.99;
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if (point < 0.01)
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point = 0.01;
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clipper_point = point;
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a = M_PI / (2.0 * (1.0 - clipper_point));
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for (i = 0; i < 6000; i++)
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clipper_lut[i] = clipper_point + atan(a * i / 1000.0) / a;
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}
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void clipper_process(sample_t *samples, int length)
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{
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int i;
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double val, inv, shiftmultval;
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int n, q;
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if (isnan(clipper_point)) {
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fprintf(stderr, "Clipper not initialized, aborting!\n");
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abort();
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}
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for (i = 0; i < length; i++) {
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val = samples[i];
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if (val < 0) {
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inv = -1.0;
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val = -val;
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} else
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inv = 1.0;
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shiftmultval = (val - clipper_point) * 1000.0;
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/* no clipping up to clipping point */
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if (shiftmultval <= 0.0)
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continue;
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n = (int)shiftmultval;
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q = n + 1;
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if (q >= 6000) {
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samples[i] = inv;
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continue;
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}
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/* get clipped value from lut, interpolate between table entries */
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val = clipper_lut[n] + (shiftmultval - (double)n) * (clipper_lut[q] - clipper_lut[n]);
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samples[i] = val * inv;
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}
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}
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