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27
28 #ifdef HAVE_CONFIG_H
29 #include "config.h"
30 #endif
31
32 #include "SigProc_FIX.h"
33
34 /* Coefficients for 2-band filter bank based on first-order allpass filters */
35 static opus_int16 A_fb1_20 = 5394 << 1;
36 static opus_int16 A_fb1_21 = -24290; /* (opus_int16)(20623 << 1) */
37
38 /* Split signal into two decimated bands using first-order allpass filters */
silk_ana_filt_bank_1(const opus_int16 * in,opus_int32 * S,opus_int16 * outL,opus_int16 * outH,const opus_int32 N)39 void silk_ana_filt_bank_1(
40 const opus_int16 *in, /* I Input signal [N] */
41 opus_int32 *S, /* I/O State vector [2] */
42 opus_int16 *outL, /* O Low band [N/2] */
43 opus_int16 *outH, /* O High band [N/2] */
44 const opus_int32 N /* I Number of input samples */
45 )
46 {
47 opus_int k, N2 = silk_RSHIFT( N, 1 );
48 opus_int32 in32, X, Y, out_1, out_2;
49
50 /* Internal variables and state are in Q10 format */
51 for( k = 0; k < N2; k++ ) {
52 /* Convert to Q10 */
53 in32 = silk_LSHIFT( (opus_int32)in[ 2 * k ], 10 );
54
55 /* All-pass section for even input sample */
56 Y = silk_SUB32( in32, S[ 0 ] );
57 X = silk_SMLAWB( Y, Y, A_fb1_21 );
58 out_1 = silk_ADD32( S[ 0 ], X );
59 S[ 0 ] = silk_ADD32( in32, X );
60
61 /* Convert to Q10 */
62 in32 = silk_LSHIFT( (opus_int32)in[ 2 * k + 1 ], 10 );
63
64 /* All-pass section for odd input sample, and add to output of previous section */
65 Y = silk_SUB32( in32, S[ 1 ] );
66 X = silk_SMULWB( Y, A_fb1_20 );
67 out_2 = silk_ADD32( S[ 1 ], X );
68 S[ 1 ] = silk_ADD32( in32, X );
69
70 /* Add/subtract, convert back to int16 and store to output */
71 outL[ k ] = (opus_int16)silk_SAT16( silk_RSHIFT_ROUND( silk_ADD32( out_2, out_1 ), 11 ) );
72 outH[ k ] = (opus_int16)silk_SAT16( silk_RSHIFT_ROUND( silk_SUB32( out_2, out_1 ), 11 ) );
73 }
74 }
75