text: /*
   *  Copyright (c) 2011 The WebRTC project authors. All Rights Reserved.
   *
   *  Use of this source code is governed by a BSD-style license
   *  that can be found in the LICENSE file in the root of the source
   *  tree. An additional intellectual property rights grant can be found
   *  in the file PATENTS.  All contributing project authors may
   *  be found in the AUTHORS file in the root of the source tree.
   */
  
  
  /*
   * This file contains the function WebRtcSpl_LpcToReflCoef().
   * The description header can be found in signal_processing_library.h
   *
   */
  
  #include "webrtc/common_audio/signal_processing/include/signal_processing_library.h"
  
  #define SPL_LPC_TO_REFL_COEF_MAX_AR_MODEL_ORDER 50
  
  void WebRtcSpl_LpcToReflCoef(int16_t* a16, int use_order, int16_t* k16)
  {
      int m, k;
      int32_t tmp32[SPL_LPC_TO_REFL_COEF_MAX_AR_MODEL_ORDER];
      int32_t tmp_inv_denom32;
      int16_t tmp_inv_denom16;
  
      k16[use_order - 1] = WEBRTC_SPL_LSHIFT_W16(a16[use_order], 3); //Q12<<3 => Q15
      for (m = use_order - 1; m > 0; m--)
      {
          // (1 - k^2) in Q30
          tmp_inv_denom32 = ((int32_t)1073741823) - WEBRTC_SPL_MUL_16_16(k16[m], k16[m]);
          // (1 - k^2) in Q15
          tmp_inv_denom16 = (int16_t)WEBRTC_SPL_RSHIFT_W32(tmp_inv_denom32, 15);
  
          for (k = 1; k <= m; k++)
          {
              // tmp[k] = (a[k] - RC[m] * a[m-k+1]) / (1.0 - RC[m]*RC[m]);
  
              // [Q12<<16 - (Q15*Q12)<<1] = [Q28 - Q28] = Q28
              tmp32[k] = WEBRTC_SPL_LSHIFT_W32((int32_t)a16[k], 16)
                      - WEBRTC_SPL_LSHIFT_W32(WEBRTC_SPL_MUL_16_16(k16[m], a16[m-k+1]), 1);
  
              tmp32[k] = WebRtcSpl_DivW32W16(tmp32[k], tmp_inv_denom16); //Q28/Q15 = Q13
          }
  
          for (k = 1; k < m; k++)
          {
              a16[k] = (int16_t)WEBRTC_SPL_RSHIFT_W32(tmp32[k], 1); //Q13>>1 => Q12
          }
  
          tmp32[m] = WEBRTC_SPL_SAT(8191, tmp32[m], -8191);
          k16[m - 1] = (int16_t)WEBRTC_SPL_LSHIFT_W32(tmp32[m], 2); //Q13<<2 => Q15
      }
      return;
  }
  