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27
28 #ifdef HAVE_CONFIG_H
29 #include "config.h"
30 #endif
31
32 #include "SigProc_FIX.h"
33
34 /* Chirp (bandwidth expand) LP AR filter */
silk_bwexpander(opus_int16 * ar,const opus_int d,opus_int32 chirp_Q16)35 void silk_bwexpander(
36 opus_int16 *ar, /* I/O AR filter to be expanded (without leading 1) */
37 const opus_int d, /* I Length of ar */
38 opus_int32 chirp_Q16 /* I Chirp factor (typically in the range 0 to 1) */
39 )
40 {
41 opus_int i;
42 opus_int32 chirp_minus_one_Q16 = chirp_Q16 - 65536;
43
44 /* NB: Dont use silk_SMULWB, instead of silk_RSHIFT_ROUND( silk_MUL(), 16 ), below. */
45 /* Bias in silk_SMULWB can lead to unstable filters */
46 for( i = 0; i < d - 1; i++ ) {
47 ar[ i ] = (opus_int16)silk_RSHIFT_ROUND( silk_MUL( chirp_Q16, ar[ i ] ), 16 );
48 chirp_Q16 += silk_RSHIFT_ROUND( silk_MUL( chirp_Q16, chirp_minus_one_Q16 ), 16 );
49 }
50 ar[ d - 1 ] = (opus_int16)silk_RSHIFT_ROUND( silk_MUL( chirp_Q16, ar[ d - 1 ] ), 16 );
51 }
52