1*a58d3d2aSXin Li /***********************************************************************
2*a58d3d2aSXin Li Copyright (c) 2006-2011, Skype Limited. All rights reserved.
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7*a58d3d2aSXin Li this list of conditions and the following disclaimer.
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26*a58d3d2aSXin Li ***********************************************************************/
27*a58d3d2aSXin Li
28*a58d3d2aSXin Li #ifdef HAVE_CONFIG_H
29*a58d3d2aSXin Li #include "config.h"
30*a58d3d2aSXin Li #endif
31*a58d3d2aSXin Li
32*a58d3d2aSXin Li #include "SigProc_FIX.h"
33*a58d3d2aSXin Li
34*a58d3d2aSXin Li /* Coefficients for 2-band filter bank based on first-order allpass filters */
35*a58d3d2aSXin Li static opus_int16 A_fb1_20 = 5394 << 1;
36*a58d3d2aSXin Li static opus_int16 A_fb1_21 = -24290; /* (opus_int16)(20623 << 1) */
37*a58d3d2aSXin Li
38*a58d3d2aSXin Li /* 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*a58d3d2aSXin Li void silk_ana_filt_bank_1(
40*a58d3d2aSXin Li const opus_int16 *in, /* I Input signal [N] */
41*a58d3d2aSXin Li opus_int32 *S, /* I/O State vector [2] */
42*a58d3d2aSXin Li opus_int16 *outL, /* O Low band [N/2] */
43*a58d3d2aSXin Li opus_int16 *outH, /* O High band [N/2] */
44*a58d3d2aSXin Li const opus_int32 N /* I Number of input samples */
45*a58d3d2aSXin Li )
46*a58d3d2aSXin Li {
47*a58d3d2aSXin Li opus_int k, N2 = silk_RSHIFT( N, 1 );
48*a58d3d2aSXin Li opus_int32 in32, X, Y, out_1, out_2;
49*a58d3d2aSXin Li
50*a58d3d2aSXin Li /* Internal variables and state are in Q10 format */
51*a58d3d2aSXin Li for( k = 0; k < N2; k++ ) {
52*a58d3d2aSXin Li /* Convert to Q10 */
53*a58d3d2aSXin Li in32 = silk_LSHIFT( (opus_int32)in[ 2 * k ], 10 );
54*a58d3d2aSXin Li
55*a58d3d2aSXin Li /* All-pass section for even input sample */
56*a58d3d2aSXin Li Y = silk_SUB32( in32, S[ 0 ] );
57*a58d3d2aSXin Li X = silk_SMLAWB( Y, Y, A_fb1_21 );
58*a58d3d2aSXin Li out_1 = silk_ADD32( S[ 0 ], X );
59*a58d3d2aSXin Li S[ 0 ] = silk_ADD32( in32, X );
60*a58d3d2aSXin Li
61*a58d3d2aSXin Li /* Convert to Q10 */
62*a58d3d2aSXin Li in32 = silk_LSHIFT( (opus_int32)in[ 2 * k + 1 ], 10 );
63*a58d3d2aSXin Li
64*a58d3d2aSXin Li /* All-pass section for odd input sample, and add to output of previous section */
65*a58d3d2aSXin Li Y = silk_SUB32( in32, S[ 1 ] );
66*a58d3d2aSXin Li X = silk_SMULWB( Y, A_fb1_20 );
67*a58d3d2aSXin Li out_2 = silk_ADD32( S[ 1 ], X );
68*a58d3d2aSXin Li S[ 1 ] = silk_ADD32( in32, X );
69*a58d3d2aSXin Li
70*a58d3d2aSXin Li /* Add/subtract, convert back to int16 and store to output */
71*a58d3d2aSXin Li outL[ k ] = (opus_int16)silk_SAT16( silk_RSHIFT_ROUND( silk_ADD32( out_2, out_1 ), 11 ) );
72*a58d3d2aSXin Li outH[ k ] = (opus_int16)silk_SAT16( silk_RSHIFT_ROUND( silk_SUB32( out_2, out_1 ), 11 ) );
73*a58d3d2aSXin Li }
74*a58d3d2aSXin Li }
75