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_LpcToReflCoef().
14 * The description header can be found in signal_processing_library.h
15 *
16 */
17
18 #include "signal_processing_library.h"
19
20 #define SPL_LPC_TO_REFL_COEF_MAX_AR_MODEL_ORDER 50
21
WebRtcSpl_LpcToReflCoef(WebRtc_Word16 * a16,int use_order,WebRtc_Word16 * k16)22 void WebRtcSpl_LpcToReflCoef(WebRtc_Word16* a16, int use_order, WebRtc_Word16* k16)
23 {
24 int m, k;
25 WebRtc_Word32 tmp32[SPL_LPC_TO_REFL_COEF_MAX_AR_MODEL_ORDER];
26 WebRtc_Word32 tmp_inv_denom32;
27 WebRtc_Word16 tmp_inv_denom16;
28
29 k16[use_order - 1] = WEBRTC_SPL_LSHIFT_W16(a16[use_order], 3); //Q12<<3 => Q15
30 for (m = use_order - 1; m > 0; m--)
31 {
32 // (1 - k^2) in Q30
33 tmp_inv_denom32 = ((WebRtc_Word32)1073741823) - WEBRTC_SPL_MUL_16_16(k16[m], k16[m]);
34 // (1 - k^2) in Q15
35 tmp_inv_denom16 = (WebRtc_Word16)WEBRTC_SPL_RSHIFT_W32(tmp_inv_denom32, 15);
36
37 for (k = 1; k <= m; k++)
38 {
39 // tmp[k] = (a[k] - RC[m] * a[m-k+1]) / (1.0 - RC[m]*RC[m]);
40
41 // [Q12<<16 - (Q15*Q12)<<1] = [Q28 - Q28] = Q28
42 tmp32[k] = WEBRTC_SPL_LSHIFT_W32((WebRtc_Word32)a16[k], 16)
43 - WEBRTC_SPL_LSHIFT_W32(WEBRTC_SPL_MUL_16_16(k16[m], a16[m-k+1]), 1);
44
45 tmp32[k] = WebRtcSpl_DivW32W16(tmp32[k], tmp_inv_denom16); //Q28/Q15 = Q13
46 }
47
48 for (k = 1; k < m; k++)
49 {
50 a16[k] = (WebRtc_Word16)WEBRTC_SPL_RSHIFT_W32(tmp32[k], 1); //Q13>>1 => Q12
51 }
52
53 tmp32[m] = WEBRTC_SPL_SAT(8191, tmp32[m], -8191);
54 k16[m - 1] = (WebRtc_Word16)WEBRTC_SPL_LSHIFT_W32(tmp32[m], 2); //Q13<<2 => Q15
55 }
56 return;
57 }
58