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_HpOutput.c
16
17 ******************************************************************/
18
19 #include "defines.h"
20
21 /*----------------------------------------------------------------*
22 * high-pass filter of output and *2 with saturation
23 *---------------------------------------------------------------*/
24
WebRtcIlbcfix_HpOutput(int16_t * signal,int16_t * ba,int16_t * y,int16_t * x,size_t len)25 void WebRtcIlbcfix_HpOutput(
26 int16_t *signal, /* (i/o) signal vector */
27 int16_t *ba, /* (i) B- and A-coefficients (2:nd order)
28 {b[0] b[1] b[2] -a[1] -a[2]} a[0]
29 is assumed to be 1.0 */
30 int16_t *y, /* (i/o) Filter state yhi[n-1] ylow[n-1]
31 yhi[n-2] ylow[n-2] */
32 int16_t *x, /* (i/o) Filter state x[n-1] x[n-2] */
33 size_t len) /* (i) Number of samples to filter */
34 {
35 size_t i;
36 int32_t tmpW32;
37 int32_t tmpW32b;
38
39 for (i=0; i<len; i++) {
40
41 /*
42 y[i] = b[0]*x[i] + b[1]*x[i-1] + b[2]*x[i-2]
43 + (-a[1])*y[i-1] + (-a[2])*y[i-2];
44 */
45
46 tmpW32 = y[1] * ba[3]; /* (-a[1])*y[i-1] (low part) */
47 tmpW32 += y[3] * ba[4]; /* (-a[2])*y[i-2] (low part) */
48 tmpW32 = (tmpW32>>15);
49 tmpW32 += y[0] * ba[3]; /* (-a[1])*y[i-1] (high part) */
50 tmpW32 += y[2] * ba[4]; /* (-a[2])*y[i-2] (high part) */
51 tmpW32 = (tmpW32<<1);
52
53 tmpW32 += signal[i] * ba[0]; /* b[0]*x[0] */
54 tmpW32 += x[0] * ba[1]; /* b[1]*x[i-1] */
55 tmpW32 += x[1] * ba[2]; /* b[2]*x[i-2] */
56
57 /* Update state (input part) */
58 x[1] = x[0];
59 x[0] = signal[i];
60
61 /* Rounding in Q(12-1), i.e. add 2^10 */
62 tmpW32b = tmpW32 + 1024;
63
64 /* Saturate (to 2^26) so that the HP filtered signal does not overflow */
65 tmpW32b = WEBRTC_SPL_SAT((int32_t)67108863, tmpW32b, (int32_t)-67108864);
66
67 /* Convert back to Q0 and multiply with 2 */
68 signal[i] = (int16_t)(tmpW32b >> 11);
69
70 /* Update state (filtered part) */
71 y[2] = y[0];
72 y[3] = y[1];
73
74 /* upshift tmpW32 by 3 with saturation */
75 if (tmpW32>268435455) {
76 tmpW32 = WEBRTC_SPL_WORD32_MAX;
77 } else if (tmpW32<-268435456) {
78 tmpW32 = WEBRTC_SPL_WORD32_MIN;
79 } else {
80 tmpW32 <<= 3;
81 }
82
83 y[0] = (int16_t)(tmpW32 >> 16);
84 y[1] = (int16_t)((tmpW32 - (y[0] << 16)) >> 1);
85
86 }
87
88 return;
89 }
90