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  * Contains the core loop function for the lattice filter AR routine
13  * for iSAC codec.
14  *
15  */
16 
17 #include "settings.h"
18 #include "signal_processing_library.h"
19 #include "webrtc/typedefs.h"
20 
21 /* Filter ar_g_Q0[] and ar_f_Q0[] through an AR filter with coefficients
22  * cth_Q15[] and sth_Q15[].
23  */
WebRtcIsacfix_FilterArLoop(int16_t * ar_g_Q0,int16_t * ar_f_Q0,int16_t * cth_Q15,int16_t * sth_Q15,size_t order_coef)24 void WebRtcIsacfix_FilterArLoop(int16_t* ar_g_Q0,     // Input samples
25                                 int16_t* ar_f_Q0,     // Input samples
26                                 int16_t* cth_Q15,     // Filter coefficients
27                                 int16_t* sth_Q15,     // Filter coefficients
28                                 size_t order_coef) { // order of the filter
29   int n = 0;
30 
31   for (n = 0; n < HALF_SUBFRAMELEN - 1; n++) {
32     size_t k = 0;
33     int16_t tmpAR = 0;
34     int32_t tmp32 = 0;
35     int32_t tmp32_2 = 0;
36 
37     tmpAR = ar_f_Q0[n + 1];
38     for (k = order_coef; k > 0; k--) {
39       tmp32 = (cth_Q15[k - 1] * tmpAR - sth_Q15[k - 1] * ar_g_Q0[k - 1] +
40                16384) >> 15;
41       tmp32_2 = (sth_Q15[k - 1] * tmpAR + cth_Q15[k - 1] * ar_g_Q0[k - 1] +
42                  16384) >> 15;
43       tmpAR   = (int16_t)WebRtcSpl_SatW32ToW16(tmp32);
44       ar_g_Q0[k] = (int16_t)WebRtcSpl_SatW32ToW16(tmp32_2);
45     }
46     ar_f_Q0[n + 1] = tmpAR;
47     ar_g_Q0[0] = tmpAR;
48   }
49 }
50