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_FilterAR().
   * The description header can be found in signal_processing_library.h
   *
   */
  
  #include "signal_processing_library.h"
  
  int WebRtcSpl_FilterAR(const int16_t* a,
                         int a_length,
                         const int16_t* x,
                         int x_length,
                         int16_t* state,
                         int state_length,
                         int16_t* state_low,
                         int state_low_length,
                         int16_t* filtered,
                         int16_t* filtered_low,
                         int filtered_low_length)
  {
      int32_t o;
      int32_t oLOW;
      int i, j, stop;
      const int16_t* x_ptr = &x[0];
      int16_t* filteredFINAL_ptr = filtered;
      int16_t* filteredFINAL_LOW_ptr = filtered_low;
  
      for (i = 0; i < x_length; i++)
      {
          // Calculate filtered[i] and filtered_low[i]
          const int16_t* a_ptr = &a[1];
          int16_t* filtered_ptr = &filtered[i - 1];
          int16_t* filtered_low_ptr = &filtered_low[i - 1];
          int16_t* state_ptr = &state[state_length - 1];
          int16_t* state_low_ptr = &state_low[state_length - 1];
  
          o = (int32_t)(*x_ptr++) << 12;
          oLOW = (int32_t)0;
  
          stop = (i < a_length) ? i + 1 : a_length;
          for (j = 1; j < stop; j++)
          {
              o -= WEBRTC_SPL_MUL_16_16(*a_ptr, *filtered_ptr--);
              oLOW -= WEBRTC_SPL_MUL_16_16(*a_ptr++, *filtered_low_ptr--);
          }
          for (j = i + 1; j < a_length; j++)
          {
              o -= WEBRTC_SPL_MUL_16_16(*a_ptr, *state_ptr--);
              oLOW -= WEBRTC_SPL_MUL_16_16(*a_ptr++, *state_low_ptr--);
          }
  
          o += (oLOW >> 12);
          *filteredFINAL_ptr = (int16_t)((o + (int32_t)2048) >> 12);
          *filteredFINAL_LOW_ptr++ = (int16_t)(o - ((int32_t)(*filteredFINAL_ptr++)
                  << 12));
      }
  
      // Save the filter state
      if (x_length >= state_length)
      {
          WebRtcSpl_CopyFromEndW16(filtered, x_length, a_length - 1, state);
          WebRtcSpl_CopyFromEndW16(filtered_low, x_length, a_length - 1, state_low);
      } else
      {
          for (i = 0; i < state_length - x_length; i++)
          {
              state[i] = state[i + x_length];
              state_low[i] = state_low[i + x_length];
          }
          for (i = 0; i < x_length; i++)
          {
              state[state_length - x_length + i] = filtered[i];
              state[state_length - x_length + i] = filtered_low[i];
          }
      }
  
      return x_length;
  }
  