Line data    Source code

       1             : /***********************************************************************
       2             : Copyright (c) 2006-2011, Skype Limited. All rights reserved.
       3             : Redistribution and use in source and binary forms, with or without
       4             : modification, are permitted provided that the following conditions
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       9             : notice, this list of conditions and the following disclaimer in the
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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"
      16             : AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
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      22             : INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
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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             : /* Chirp (bandwidth expand) LP AR filter */
      35           0 : void silk_bwexpander(
      36             :     opus_int16                  *ar,                /* I/O  AR filter to be expanded (without leading 1)                */
      37             :     const opus_int              d,                  /* I    Length of ar                                                */
      38             :     opus_int32                  chirp_Q16           /* I    Chirp factor (typically in the range 0 to 1)                */
      39             : )
      40             : {
      41             :     opus_int   i;
      42           0 :     opus_int32 chirp_minus_one_Q16 = chirp_Q16 - 65536;
      43             : 
      44             :     /* NB: Dont use silk_SMULWB, instead of silk_RSHIFT_ROUND( silk_MUL(), 16 ), below.  */
      45             :     /* Bias in silk_SMULWB can lead to unstable filters                                */
      46           0 :     for( i = 0; i < d - 1; i++ ) {
      47           0 :         ar[ i ]    = (opus_int16)silk_RSHIFT_ROUND( silk_MUL( chirp_Q16, ar[ i ]             ), 16 );
      48           0 :         chirp_Q16 +=             silk_RSHIFT_ROUND( silk_MUL( chirp_Q16, chirp_minus_one_Q16 ), 16 );
      49             :     }
      50           0 :     ar[ d - 1 ] = (opus_int16)silk_RSHIFT_ROUND( silk_MUL( chirp_Q16, ar[ d - 1 ] ), 16 );
      51           0 : }