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      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_FilterAR().
     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 size_t WebRtcSpl_FilterAR(const int16_t* a,
     21                           size_t a_length,
     22                           const int16_t* x,
     23                           size_t x_length,
     24                           int16_t* state,
     25                           size_t state_length,
     26                           int16_t* state_low,
     27                           size_t state_low_length,
     28                           int16_t* filtered,
     29                           int16_t* filtered_low,
     30                           size_t filtered_low_length)
     31 {
     32     int32_t o;
     33     int32_t oLOW;
     34     size_t i, j, stop;
     35     const int16_t* x_ptr = &x[0];
     36     int16_t* filteredFINAL_ptr = filtered;
     37     int16_t* filteredFINAL_LOW_ptr = filtered_low;
     38 
     39     for (i = 0; i < x_length; i++)
     40     {
     41         // Calculate filtered[i] and filtered_low[i]
     42         const int16_t* a_ptr = &a[1];
     43         int16_t* filtered_ptr = &filtered[i - 1];
     44         int16_t* filtered_low_ptr = &filtered_low[i - 1];
     45         int16_t* state_ptr = &state[state_length - 1];
     46         int16_t* state_low_ptr = &state_low[state_length - 1];
     47 
     48         o = (int32_t)(*x_ptr++) << 12;
     49         oLOW = (int32_t)0;
     50 
     51         stop = (i < a_length) ? i + 1 : a_length;
     52         for (j = 1; j < stop; j++)
     53         {
     54           o -= *a_ptr * *filtered_ptr--;
     55           oLOW -= *a_ptr++ * *filtered_low_ptr--;
     56         }
     57         for (j = i + 1; j < a_length; j++)
     58         {
     59           o -= *a_ptr * *state_ptr--;
     60           oLOW -= *a_ptr++ * *state_low_ptr--;
     61         }
     62 
     63         o += (oLOW >> 12);
     64         *filteredFINAL_ptr = (int16_t)((o + (int32_t)2048) >> 12);
     65         *filteredFINAL_LOW_ptr++ = (int16_t)(o - ((int32_t)(*filteredFINAL_ptr++)
     66                 << 12));
     67     }
     68 
     69     // Save the filter state
     70     if (x_length >= state_length)
     71     {
     72         WebRtcSpl_CopyFromEndW16(filtered, x_length, a_length - 1, state);
     73         WebRtcSpl_CopyFromEndW16(filtered_low, x_length, a_length - 1, state_low);
     74     } else
     75     {
     76         for (i = 0; i < state_length - x_length; i++)
     77         {
     78             state[i] = state[i + x_length];
     79             state_low[i] = state_low[i + x_length];
     80         }
     81         for (i = 0; i < x_length; i++)
     82         {
     83             state[state_length - x_length + i] = filtered[i];
     84             state[state_length - x_length + i] = filtered_low[i];
     85         }
     86     }
     87 
     88     return x_length;
     89 }
     90