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 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
