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source: webrtc/webrtc/modules/audio_coding/codecs/ilbc/lsf_to_poly.c @ 0:4bda6873e34c

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Last change on this file since 0:4bda6873e34c was 0:4bda6873e34c, checked in by Michael Prittie <mprittie@…>, 6 years ago

Scrubbed password for publication.

File size: 2.1 KB
Line 
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 iLBC Speech Coder ANSI-C Source Code
14
15 WebRtcIlbcfix_Lsf2Poly.c
16
17******************************************************************/
18
19#include "defines.h"
20#include "lsf_to_lsp.h"
21#include "get_lsp_poly.h"
22#include "constants.h"
23
24void WebRtcIlbcfix_Lsf2Poly(
25    int16_t *a,     /* (o) predictor coefficients (order = 10) in Q12 */
26    int16_t *lsf    /* (i) line spectral frequencies in Q13 */
27                            ) {
28  int32_t f[2][6]; /* f[0][] and f[1][] corresponds to
29                            F1(z) and F2(z) respectivly */
30  int32_t *f1ptr, *f2ptr;
31  int16_t *a1ptr, *a2ptr;
32  int32_t tmpW32;
33  int16_t lsp[10];
34  int i;
35
36  /* Convert lsf to lsp */
37  WebRtcIlbcfix_Lsf2Lsp(lsf, lsp, LPC_FILTERORDER);
38
39  /* Get F1(z) and F2(z) from the lsp */
40  f1ptr=f[0];
41  f2ptr=f[1];
42  WebRtcIlbcfix_GetLspPoly(&lsp[0],f1ptr);
43  WebRtcIlbcfix_GetLspPoly(&lsp[1],f2ptr);
44
45  /* for i = 5 down to 1
46     Compute f1[i] += f1[i-1];
47     and     f2[i] += f2[i-1];
48  */
49  f1ptr=&f[0][5];
50  f2ptr=&f[1][5];
51  for (i=5; i>0; i--)
52  {
53    (*f1ptr) += (*(f1ptr-1));
54    (*f2ptr) -= (*(f2ptr-1));
55    f1ptr--;
56    f2ptr--;
57  }
58
59  /* Get the A(z) coefficients
60     a[0] = 1.0
61     for i = 1 to 5
62     a[i] = (f1[i] + f2[i] + round)>>13;
63     for i = 1 to 5
64     a[11-i] = (f1[i] - f2[i] + round)>>13;
65  */
66  a[0]=4096;
67  a1ptr=&a[1];
68  a2ptr=&a[10];
69  f1ptr=&f[0][1];
70  f2ptr=&f[1][1];
71  for (i=5; i>0; i--)
72  {
73    tmpW32 = (*f1ptr) + (*f2ptr);
74    (*a1ptr) = (int16_t)WEBRTC_SPL_RSHIFT_W32((tmpW32+4096),13);
75
76    tmpW32 = (*f1ptr) - (*f2ptr);
77    (*a2ptr) = (int16_t)WEBRTC_SPL_RSHIFT_W32((tmpW32+4096),13);
78
79    a1ptr++;
80    a2ptr--;
81    f1ptr++;
82    f2ptr++;
83  }
84
85  return;
86}
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