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/*
* Copyright (c) 2011 The WebRTC project authors. All Rights Reserved.
*
* Use of this source code is governed by a BSD-style license
* that can be found in the LICENSE file in the root of the source
* tree. An additional intellectual property rights grant can be found
* in the file PATENTS. All contributing project authors may
* be found in the AUTHORS file in the root of the source tree.
*/
/******************************************************************
iLBC Speech Coder ANSI-C Source Code
WebRtcIlbcfix_HpInput.c
******************************************************************/
#include "modules/audio_coding/codecs/ilbc/hp_input.h"
#include "modules/audio_coding/codecs/ilbc/defines.h"
/*----------------------------------------------------------------*
* high-pass filter of input with *0.5 and saturation
*---------------------------------------------------------------*/
void WebRtcIlbcfix_HpInput(
int16_t *signal, /* (i/o) signal vector */
int16_t *ba, /* (i) B- and A-coefficients (2:nd order)
{b[0] b[1] b[2] -a[1] -a[2]} a[0]
is assumed to be 1.0 */
int16_t *y, /* (i/o) Filter state yhi[n-1] ylow[n-1]
yhi[n-2] ylow[n-2] */
int16_t *x, /* (i/o) Filter state x[n-1] x[n-2] */
size_t len) /* (i) Number of samples to filter */
{
size_t i;
int32_t tmpW32;
int32_t tmpW32b;
for (i=0; i<len; i++) {
/*
y[i] = b[0]*x[i] + b[1]*x[i-1] + b[2]*x[i-2]
+ (-a[1])*y[i-1] + (-a[2])*y[i-2];
*/
tmpW32 = y[1] * ba[3]; /* (-a[1])*y[i-1] (low part) */
tmpW32 += y[3] * ba[4]; /* (-a[2])*y[i-2] (low part) */
tmpW32 = (tmpW32>>15);
tmpW32 += y[0] * ba[3]; /* (-a[1])*y[i-1] (high part) */
tmpW32 += y[2] * ba[4]; /* (-a[2])*y[i-2] (high part) */
tmpW32 = (tmpW32<<1);
tmpW32 += signal[i] * ba[0]; /* b[0]*x[0] */
tmpW32 += x[0] * ba[1]; /* b[1]*x[i-1] */
tmpW32 += x[1] * ba[2]; /* b[2]*x[i-2] */
/* Update state (input part) */
x[1] = x[0];
x[0] = signal[i];
/* Rounding in Q(12+1), i.e. add 2^12 */
tmpW32b = tmpW32 + 4096;
/* Saturate (to 2^28) so that the HP filtered signal does not overflow */
tmpW32b = WEBRTC_SPL_SAT((int32_t)268435455, tmpW32b, (int32_t)-268435456);
/* Convert back to Q0 and multiply with 0.5 */
signal[i] = (int16_t)(tmpW32b >> 13);
/* Update state (filtered part) */
y[2] = y[0];
y[3] = y[1];
/* upshift tmpW32 by 3 with saturation */
if (tmpW32>268435455) {
tmpW32 = WEBRTC_SPL_WORD32_MAX;
} else if (tmpW32<-268435456) {
tmpW32 = WEBRTC_SPL_WORD32_MIN;
} else {
tmpW32 <<= 3;
}
y[0] = (int16_t)(tmpW32 >> 16);
y[1] = (int16_t)((tmpW32 - (y[0] << 16)) >> 1);
}
return;
}
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