1*a58d3d2aSXin Li /***********************************************************************
2*a58d3d2aSXin Li Copyright (c) 2006-2011, Skype Limited. All rights reserved.
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4*a58d3d2aSXin Li modification, are permitted provided that the following conditions
5*a58d3d2aSXin Li are met:
6*a58d3d2aSXin Li - Redistributions of source code must retain the above copyright notice,
7*a58d3d2aSXin Li this list of conditions and the following disclaimer.
8*a58d3d2aSXin Li - Redistributions in binary form must reproduce the above copyright
9*a58d3d2aSXin Li notice, this list of conditions and the following disclaimer in the
10*a58d3d2aSXin Li documentation and/or other materials provided with the distribution.
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13*a58d3d2aSXin Li products derived from this software without specific prior written
14*a58d3d2aSXin Li permission.
15*a58d3d2aSXin Li THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
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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 #include "resampler_rom.h"
34*a58d3d2aSXin Li
35*a58d3d2aSXin Li /* Downsample by a factor 2 */
silk_resampler_down2(opus_int32 * S,opus_int16 * out,const opus_int16 * in,opus_int32 inLen)36*a58d3d2aSXin Li void silk_resampler_down2(
37*a58d3d2aSXin Li opus_int32 *S, /* I/O State vector [ 2 ] */
38*a58d3d2aSXin Li opus_int16 *out, /* O Output signal [ floor(len/2) ] */
39*a58d3d2aSXin Li const opus_int16 *in, /* I Input signal [ len ] */
40*a58d3d2aSXin Li opus_int32 inLen /* I Number of input samples */
41*a58d3d2aSXin Li )
42*a58d3d2aSXin Li {
43*a58d3d2aSXin Li opus_int32 k, len2 = silk_RSHIFT32( inLen, 1 );
44*a58d3d2aSXin Li opus_int32 in32, out32, Y, X;
45*a58d3d2aSXin Li
46*a58d3d2aSXin Li celt_assert( silk_resampler_down2_0 > 0 );
47*a58d3d2aSXin Li celt_assert( silk_resampler_down2_1 < 0 );
48*a58d3d2aSXin Li
49*a58d3d2aSXin Li /* Internal variables and state are in Q10 format */
50*a58d3d2aSXin Li for( k = 0; k < len2; k++ ) {
51*a58d3d2aSXin Li /* Convert to Q10 */
52*a58d3d2aSXin Li in32 = silk_LSHIFT( (opus_int32)in[ 2 * k ], 10 );
53*a58d3d2aSXin Li
54*a58d3d2aSXin Li /* All-pass section for even input sample */
55*a58d3d2aSXin Li Y = silk_SUB32( in32, S[ 0 ] );
56*a58d3d2aSXin Li X = silk_SMLAWB( Y, Y, silk_resampler_down2_1 );
57*a58d3d2aSXin Li out32 = silk_ADD32( S[ 0 ], X );
58*a58d3d2aSXin Li S[ 0 ] = silk_ADD32( in32, X );
59*a58d3d2aSXin Li
60*a58d3d2aSXin Li /* Convert to Q10 */
61*a58d3d2aSXin Li in32 = silk_LSHIFT( (opus_int32)in[ 2 * k + 1 ], 10 );
62*a58d3d2aSXin Li
63*a58d3d2aSXin Li /* All-pass section for odd input sample, and add to output of previous section */
64*a58d3d2aSXin Li Y = silk_SUB32( in32, S[ 1 ] );
65*a58d3d2aSXin Li X = silk_SMULWB( Y, silk_resampler_down2_0 );
66*a58d3d2aSXin Li out32 = silk_ADD32( out32, S[ 1 ] );
67*a58d3d2aSXin Li out32 = silk_ADD32( out32, X );
68*a58d3d2aSXin Li S[ 1 ] = silk_ADD32( in32, X );
69*a58d3d2aSXin Li
70*a58d3d2aSXin Li /* Add, convert back to int16 and store to output */
71*a58d3d2aSXin Li out[ k ] = (opus_int16)silk_SAT16( silk_RSHIFT_ROUND( out32, 11 ) );
72*a58d3d2aSXin Li }
73*a58d3d2aSXin Li }
74*a58d3d2aSXin Li
75