ref: 2af92cd99f1f78f596a49dc951d17faeb9363dd3
dir: /silk/bwexpander.c/
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#ifdef HAVE_CONFIG_H
#include "config.h"
#endif
#include "SigProc_FIX.h"
/* Chirp (bandwidth expand) LP AR filter */
void silk_bwexpander(
opus_int16 *ar, /* I/O AR filter to be expanded (without leading 1) */
const opus_int d, /* I Length of ar */
opus_int32 chirp_Q16 /* I Chirp factor (typically in the range 0 to 1) */
)
{
opus_int i;
opus_int32 chirp_minus_one_Q16 = chirp_Q16 - 65536;
/* NB: Dont use silk_SMULWB, instead of silk_RSHIFT_ROUND( silk_MUL(), 16 ), below. */
/* Bias in silk_SMULWB can lead to unstable filters */
for( i = 0; i < d - 1; i++ ) {
ar[ i ] = (opus_int16)silk_RSHIFT_ROUND( silk_MUL( chirp_Q16, ar[ i ] ), 16 );
chirp_Q16 += silk_RSHIFT_ROUND( silk_MUL( chirp_Q16, chirp_minus_one_Q16 ), 16 );
}
ar[ d - 1 ] = (opus_int16)silk_RSHIFT_ROUND( silk_MUL( chirp_Q16, ar[ d - 1 ] ), 16 );
}