mirror of https://git.ffmpeg.org/ffmpeg.git
avcodec/kbdwin: Avoid computing bessel values twice
Also reduce neeeded temporary storage by half Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>
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@ -23,23 +23,29 @@
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av_cold void ff_kbd_window_init(float *window, float alpha, int n)
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{
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int i, j;
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double sum = 0.0, bessel, tmp;
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double local_window[FF_KBD_WINDOW_MAX];
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double alpha2 = (alpha * M_PI / n) * (alpha * M_PI / n);
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int i;
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double sum = 0.0, tmp;
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double scale = 0.0;
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double temp[FF_KBD_WINDOW_MAX / 2 + 1];
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double alpha2 = 4 * (alpha * M_PI / n) * (alpha * M_PI / n);
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av_assert0(n <= FF_KBD_WINDOW_MAX);
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for (i = 0; i < n; i++) {
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for (i = 0; i <= n / 2; i++) {
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tmp = i * (n - i) * alpha2;
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bessel = av_bessel_i0(sqrt(tmp) * 2);
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sum += bessel;
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local_window[i] = sum;
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temp[i] = av_bessel_i0(sqrt(tmp));
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scale += temp[i] * (1 + (i && i<n/2));
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}
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scale = 1.0/(scale + 1);
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sum++;
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for (i = 0; i < n; i++)
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window[i] = sqrt(local_window[i] / sum);
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for (i = 0; i <= n / 2; i++) {
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sum += temp[i];
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window[i] = sqrt(sum * scale);
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}
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for (; i < n; i++) {
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sum += temp[n - i];
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window[i] = sqrt(sum * scale);
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}
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}
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av_cold void ff_kbd_window_init_fixed(int32_t *window, float alpha, int n)
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