1 /***********************************************************************
2 Copyright (c) 2013, Koen Vos. All rights reserved.
3 Redistribution and use in source and binary forms, with or without
4 modification, are permitted provided that the following conditions
5 are met:
6 - Redistributions of source code must retain the above copyright notice,
7 this list of conditions and the following disclaimer.
8 - Redistributions in binary form must reproduce the above copyright
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13 products derived from this software without specific prior written
14 permission.
15 THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
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17 IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
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24 ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
25 POSSIBILITY OF SUCH DAMAGE.
26 ***********************************************************************/
27 
28 #ifdef HAVE_CONFIG_H
29 #include "config.h"
30 #endif
31 
32 #include "SigProc_FIX.h"
33 
34 /* Convert int32 coefficients to int16 coefs and make sure there's no wrap-around */
silk_LPC_fit(opus_int16 * a_QOUT,opus_int32 * a_QIN,const opus_int QOUT,const opus_int QIN,const opus_int d)35 void silk_LPC_fit(
36     opus_int16                  *a_QOUT,            /* O    Output signal                                               */
37     opus_int32                    *a_QIN,             /* I/O  Input signal                                                */
38     const opus_int              QOUT,               /* I    Input Q domain                                              */
39     const opus_int              QIN,                /* I    Input Q domain                                              */
40     const opus_int              d                   /* I    Filter order                                                */
41 )
42 {
43     opus_int    i, k, idx = 0;
44     opus_int32    maxabs, absval, chirp_Q16;
45 
46     /* Limit the maximum absolute value of the prediction coefficients, so that they'll fit in int16 */
47     for( i = 0; i < 10; i++ ) {
48         /* Find maximum absolute value and its index */
49         maxabs = 0;
50         for( k = 0; k < d; k++ ) {
51             absval = silk_abs( a_QIN[k] );
52             if( absval > maxabs ) {
53                 maxabs = absval;
54                 idx    = k;
55             }
56         }
57         maxabs = silk_RSHIFT_ROUND( maxabs, QIN - QOUT );
58 
59         if( maxabs > silk_int16_MAX ) {
60             /* Reduce magnitude of prediction coefficients */
61             maxabs = silk_min( maxabs, 163838 );  /* ( silk_int32_MAX >> 14 ) + silk_int16_MAX = 163838 */
62             chirp_Q16 = SILK_FIX_CONST( 0.999, 16 ) - silk_DIV32( silk_LSHIFT( maxabs - silk_int16_MAX, 14 ),
63                                         silk_RSHIFT32( silk_MUL( maxabs, idx + 1), 2 ) );
64             silk_bwexpander_32( a_QIN, d, chirp_Q16 );
65         } else {
66             break;
67         }
68     }
69 
70     if( i == 10 ) {
71         /* Reached the last iteration, clip the coefficients */
72         for( k = 0; k < d; k++ ) {
73             a_QOUT[ k ] = (opus_int16)silk_SAT16( silk_RSHIFT_ROUND( a_QIN[ k ], QIN - QOUT ) );
74             a_QIN[ k ] = silk_LSHIFT( (opus_int32)a_QOUT[ k ], QIN - QOUT );
75         }
76     } else {
77         for( k = 0; k < d; k++ ) {
78             a_QOUT[ k ] = (opus_int16)silk_RSHIFT_ROUND( a_QIN[ k ], QIN - QOUT );
79         }
80     }
81 }
82