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/* Hilbert function
*
* Copyright © 2021 Wim Taymans
*
* Permission is hereby granted, free of charge, to any person obtaining a
* copy of this software and associated documentation files (the "Software"),
* to deal in the Software without restriction, including without limitation
* the rights to use, copy, modify, merge, publish, distribute, sublicense,
* and/or sell copies of the Software, and to permit persons to whom the
* Software is furnished to do so, subject to the following conditions:
*
* The above copyright notice and this permission notice (including the next
* paragraph) shall be included in all copies or substantial portions of the
* Software.
*
* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
* IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
* FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL
* THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
* LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
* FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
* DEALINGS IN THE SOFTWARE.
*/
#ifndef HILBERT_H
#define HILBERT_H
#ifdef __cplusplus
extern "C" {
#endif
#include <errno.h>
#include <stddef.h>
#include <math.h>
static inline void blackman_window(float *taps, int n_taps)
{
int n;
for (n = 0; n < n_taps; n++) {
float w = 2 * M_PI * n / (n_taps-1);
taps[n] = 0.3635819 - 0.4891775 * cos(w)
+ 0.1365995 * cos(2 * w) - 0.0106411 * cos(3 * w);
}
}
static inline int hilbert_generate(float *taps, int n_taps)
{
int i;
if ((n_taps & 1) == 0)
return -EINVAL;
for (i = 0; i < n_taps; i++) {
int k = -(n_taps / 2) + i;
if (k & 1) {
float pk = M_PI * k;
taps[i] *= (1.0f - cosf(pk)) / pk;
} else {
taps[i] = 0.0f;
}
}
return 0;
}
#ifdef __cplusplus
} /* extern "C" */
#endif
#endif /* HILBERT_H */
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