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 "defines.h"
20
21/*----------------------------------------------------------------*
22 *  high-pass filter of input with *0.5 and saturation
23 *---------------------------------------------------------------*/
24
25void WebRtcIlbcfix_HpInput(
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    int16_t len)      /* (i)   Number of samples to filter */
34{
35  int 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  = WEBRTC_SPL_MUL_16_16(y[1], ba[3]);     /* (-a[1])*y[i-1] (low part) */
47    tmpW32 += WEBRTC_SPL_MUL_16_16(y[3], ba[4]);     /* (-a[2])*y[i-2] (low part) */
48    tmpW32 = (tmpW32>>15);
49    tmpW32 += WEBRTC_SPL_MUL_16_16(y[0], ba[3]);     /* (-a[1])*y[i-1] (high part) */
50    tmpW32 += WEBRTC_SPL_MUL_16_16(y[2], ba[4]);     /* (-a[2])*y[i-2] (high part) */
51    tmpW32 = (tmpW32<<1);
52
53    tmpW32 += WEBRTC_SPL_MUL_16_16(signal[i], ba[0]);   /* b[0]*x[0] */
54    tmpW32 += WEBRTC_SPL_MUL_16_16(x[0],      ba[1]);   /* b[1]*x[i-1] */
55    tmpW32 += WEBRTC_SPL_MUL_16_16(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 2^12 */
62    tmpW32b = tmpW32 + 4096;
63
64    /* Saturate (to 2^28) so that the HP filtered signal does not overflow */
65    tmpW32b = WEBRTC_SPL_SAT((int32_t)268435455, tmpW32b, (int32_t)-268435456);
66
67    /* Convert back to Q0 and multiply with 0.5 */
68    signal[i] = (int16_t)WEBRTC_SPL_RSHIFT_W32(tmpW32b, 13);
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 = WEBRTC_SPL_LSHIFT_W32(tmpW32, 3);
81    }
82
83    y[0] = (int16_t)(tmpW32 >> 16);
84    y[1] = (int16_t)((tmpW32 - WEBRTC_SPL_LSHIFT_W32((int32_t)y[0], 16))>>1);
85  }
86
87  return;
88}
89