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avfilter/window_func: Use av_bessel_i0()

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Old code needed about 6 times as long as new with defaults in afftfilt

Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>
This commit is contained in:
Michael Niedermayer 2023-05-23 00:03:31 +02:00
parent 1e9c337e0f
commit 0c7a0514e3
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GPG Key ID: B18E8928B3948D64
1 changed files with 4 additions and 15 deletions
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19
libavfilter/window_func.h
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@ -59,19 +59,6 @@ enum WindowFunc { WFUNC_RECT, WFUNC_HANNING, WFUNC_HAMMING, WFUNC_BLACKMAN,
{ "bohman", "Bohman", 0, AV_OPT_TYPE_CONST, {.i64=WFUNC_BOHMAN}, 0, 0, flag, "win_func" }, \
{ "kaiser", "Kaiser", 0, AV_OPT_TYPE_CONST, {.i64=WFUNC_KAISER}, 0, 0, flag, "win_func" }
static inline double get_i0(double x)
{
double y = 1.0, prev = 1.0, i = 1.0;
while (fabs(prev) > 1e-20) {
double summand = prev * x * x / (4 * i * i);
y += summand;
prev = summand;
i++;
}
return y;
}
static inline void generate_window_func(float *lut, int N, int win_func,
float *overlap)
@ -232,13 +219,15 @@ static inline void generate_window_func(float *lut, int N, int win_func,
*overlap = 0.75;
break;
case WFUNC_KAISER:
{
double scale = 1.0 / av_bessel_i0(12.);
for (n = 0; n < N; n++) {
double x = 2.0 / (double)(N - 1);
lut[n] = get_i0(12. * sqrt(1. - SQR(n * x - 1.))) / get_i0(12.);
lut[n] = av_bessel_i0(12. * sqrt(1. - SQR(n * x - 1.))) * scale;
}
*overlap = 0.75;
break;
}
default:
av_assert0(0);
}