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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 
WebRtcSpl_FilterAR(const int16_t * a,size_t a_length,const int16_t * x,size_t x_length,int16_t * state,size_t state_length,int16_t * state_low,size_t state_low_length,int16_t * filtered,int16_t * filtered_low,size_t filtered_low_length)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