chromium/third_party/opus/src/silk/LP_variable_cutoff.c

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#ifdef HAVE_CONFIG_H
#include "config.h"
#endif

/*
    Elliptic/Cauer filters designed with 0.1 dB passband ripple,
    80 dB minimum stopband attenuation, and
    [0.95 : 0.15 : 0.35] normalized cut off frequencies.
*/

#include "main.h"

/* Helper function, interpolates the filter taps */
static OPUS_INLINE void silk_LP_interpolate_filter_taps(
    opus_int32           B_Q28[ TRANSITION_NB ],
    opus_int32           A_Q28[ TRANSITION_NA ],
    const opus_int       ind,
    const opus_int32     fac_Q16
)
{ … }

/* Low-pass filter with variable cutoff frequency based on  */
/* piece-wise linear interpolation between elliptic filters */
/* Start by setting psEncC->mode <> 0;                      */
/* Deactivate by setting psEncC->mode = 0;                  */
void silk_LP_variable_cutoff(
    silk_LP_state               *psLP,                          /* I/O  LP filter state                             */
    opus_int16                  *frame,                         /* I/O  Low-pass filtered output signal             */
    const opus_int              frame_length                    /* I    Frame length                                */
)
{ … }