ref: a156c5ece7133383468d4cba33f067595d9da391
dir: /silk/ana_filt_bank_1.c/
/***********************************************************************
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#ifdef HAVE_CONFIG_H
#include "config.h"
#endif
#include "SigProc_FIX.h"
/* Coefficients for 2-band filter bank based on first-order allpass filters */
static opus_int16 A_fb1_20 = 5394 << 1;
static opus_int16 A_fb1_21 = -24290; /* (opus_int16)(20623 << 1) */
/* Split signal into two decimated bands using first-order allpass filters */
void silk_ana_filt_bank_1(
const opus_int16 *in, /* I Input signal [N] */
opus_int32 *S, /* I/O State vector [2] */
opus_int16 *outL, /* O Low band [N/2] */
opus_int16 *outH, /* O High band [N/2] */
const opus_int32 N /* I Number of input samples */
)
{
opus_int k, N2 = silk_RSHIFT( N, 1 );
opus_int32 in32, X, Y, out_1, out_2;
/* Internal variables and state are in Q10 format */
for( k = 0; k < N2; k++ ) {
/* Convert to Q10 */
in32 = silk_LSHIFT( (opus_int32)in[ 2 * k ], 10 );
/* All-pass section for even input sample */
Y = silk_SUB32( in32, S[ 0 ] );
X = silk_SMLAWB( Y, Y, A_fb1_21 );
out_1 = silk_ADD32( S[ 0 ], X );
S[ 0 ] = silk_ADD32( in32, X );
/* Convert to Q10 */
in32 = silk_LSHIFT( (opus_int32)in[ 2 * k + 1 ], 10 );
/* All-pass section for odd input sample, and add to output of previous section */
Y = silk_SUB32( in32, S[ 1 ] );
X = silk_SMULWB( Y, A_fb1_20 );
out_2 = silk_ADD32( S[ 1 ], X );
S[ 1 ] = silk_ADD32( in32, X );
/* Add/subtract, convert back to int16 and store to output */
outL[ k ] = (opus_int16)silk_SAT16( silk_RSHIFT_ROUND( silk_ADD32( out_2, out_1 ), 11 ) );
outH[ k ] = (opus_int16)silk_SAT16( silk_RSHIFT_ROUND( silk_SUB32( out_2, out_1 ), 11 ) );
}
}