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_HpInput.c
16
17 ******************************************************************/
18
19 #include "modules/audio_coding/codecs/ilbc/hp_input.h"
20
21 #include "modules/audio_coding/codecs/ilbc/defines.h"
22
23 /*----------------------------------------------------------------*
24 * high-pass filter of input with *0.5 and saturation
25 *---------------------------------------------------------------*/
26
WebRtcIlbcfix_HpInput(int16_t * signal,int16_t * ba,int16_t * y,int16_t * x,size_t len)27 void WebRtcIlbcfix_HpInput(
28 int16_t *signal, /* (i/o) signal vector */
29 int16_t *ba, /* (i) B- and A-coefficients (2:nd order)
30 {b[0] b[1] b[2] -a[1] -a[2]} a[0]
31 is assumed to be 1.0 */
32 int16_t *y, /* (i/o) Filter state yhi[n-1] ylow[n-1]
33 yhi[n-2] ylow[n-2] */
34 int16_t *x, /* (i/o) Filter state x[n-1] x[n-2] */
35 size_t len) /* (i) Number of samples to filter */
36 {
37 size_t i;
38 int32_t tmpW32;
39 int32_t tmpW32b;
40
41 for (i=0; i<len; i++) {
42
43 /*
44 y[i] = b[0]*x[i] + b[1]*x[i-1] + b[2]*x[i-2]
45 + (-a[1])*y[i-1] + (-a[2])*y[i-2];
46 */
47
48 tmpW32 = y[1] * ba[3]; /* (-a[1])*y[i-1] (low part) */
49 tmpW32 += y[3] * ba[4]; /* (-a[2])*y[i-2] (low part) */
50 tmpW32 = (tmpW32>>15);
51 tmpW32 += y[0] * ba[3]; /* (-a[1])*y[i-1] (high part) */
52 tmpW32 += y[2] * ba[4]; /* (-a[2])*y[i-2] (high part) */
53 tmpW32 = (tmpW32<<1);
54
55 tmpW32 += signal[i] * ba[0]; /* b[0]*x[0] */
56 tmpW32 += x[0] * ba[1]; /* b[1]*x[i-1] */
57 tmpW32 += x[1] * ba[2]; /* b[2]*x[i-2] */
58
59 /* Update state (input part) */
60 x[1] = x[0];
61 x[0] = signal[i];
62
63 /* Rounding in Q(12+1), i.e. add 2^12 */
64 tmpW32b = tmpW32 + 4096;
65
66 /* Saturate (to 2^28) so that the HP filtered signal does not overflow */
67 tmpW32b = WEBRTC_SPL_SAT((int32_t)268435455, tmpW32b, (int32_t)-268435456);
68
69 /* Convert back to Q0 and multiply with 0.5 */
70 signal[i] = (int16_t)(tmpW32b >> 13);
71
72 /* Update state (filtered part) */
73 y[2] = y[0];
74 y[3] = y[1];
75
76 /* upshift tmpW32 by 3 with saturation */
77 if (tmpW32>268435455) {
78 tmpW32 = WEBRTC_SPL_WORD32_MAX;
79 } else if (tmpW32<-268435456) {
80 tmpW32 = WEBRTC_SPL_WORD32_MIN;
81 } else {
82 tmpW32 <<= 3;
83 }
84
85 y[0] = (int16_t)(tmpW32 >> 16);
86 y[1] = (int16_t)((tmpW32 - (y[0] << 16)) >> 1);
87 }
88
89 return;
90 }
91