Line data    Source code

       1             : /*
       2             :  *  Copyright (c) 2011 The WebRTC project authors. All Rights Reserved.
       3             :  *
       4             :  *  Use of this source code is governed by a BSD-style license
       5             :  *  that can be found in the LICENSE file in the root of the source
       6             :  *  tree. An additional intellectual property rights grant can be found
       7             :  *  in the file PATENTS.  All contributing project authors may
       8             :  *  be found in the AUTHORS file in the root of the source tree.
       9             :  */
      10             : 
      11             : 
      12             : /*
      13             :  * This file contains the function WebRtcSpl_LpcToReflCoef().
      14             :  * The description header can be found in signal_processing_library.h
      15             :  *
      16             :  */
      17             : 
      18             : #include "webrtc/common_audio/signal_processing/include/signal_processing_library.h"
      19             : 
      20             : #define SPL_LPC_TO_REFL_COEF_MAX_AR_MODEL_ORDER 50
      21             : 
      22           0 : void WebRtcSpl_LpcToReflCoef(int16_t* a16, int use_order, int16_t* k16)
      23             : {
      24             :     int m, k;
      25             :     int32_t tmp32[SPL_LPC_TO_REFL_COEF_MAX_AR_MODEL_ORDER];
      26             :     int32_t tmp_inv_denom32;
      27             :     int16_t tmp_inv_denom16;
      28             : 
      29           0 :     k16[use_order - 1] = a16[use_order] << 3;  // Q12<<3 => Q15
      30           0 :     for (m = use_order - 1; m > 0; m--)
      31             :     {
      32             :         // (1 - k^2) in Q30
      33           0 :         tmp_inv_denom32 = 1073741823 - k16[m] * k16[m];
      34             :         // (1 - k^2) in Q15
      35           0 :         tmp_inv_denom16 = (int16_t)(tmp_inv_denom32 >> 15);
      36             : 
      37           0 :         for (k = 1; k <= m; k++)
      38             :         {
      39             :             // tmp[k] = (a[k] - RC[m] * a[m-k+1]) / (1.0 - RC[m]*RC[m]);
      40             : 
      41             :             // [Q12<<16 - (Q15*Q12)<<1] = [Q28 - Q28] = Q28
      42           0 :             tmp32[k] = (a16[k] << 16) - (k16[m] * a16[m - k + 1] << 1);
      43             : 
      44           0 :             tmp32[k] = WebRtcSpl_DivW32W16(tmp32[k], tmp_inv_denom16); //Q28/Q15 = Q13
      45             :         }
      46             : 
      47           0 :         for (k = 1; k < m; k++)
      48             :         {
      49           0 :             a16[k] = (int16_t)(tmp32[k] >> 1);  // Q13>>1 => Q12
      50             :         }
      51             : 
      52           0 :         tmp32[m] = WEBRTC_SPL_SAT(8191, tmp32[m], -8191);
      53           0 :         k16[m - 1] = (int16_t)WEBRTC_SPL_LSHIFT_W32(tmp32[m], 2); //Q13<<2 => Q15
      54             :     }
      55           0 :     return;
      56             : }