77 lines
2.1 KiB
C
77 lines
2.1 KiB
C
/*
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* iLBC - a library for the iLBC codec
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*
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* anaFilter.c - The iLBC low bit rate speech codec.
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*
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* Adapted by Steve Underwood <steveu@coppice.org> from the reference
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* iLBC code supplied in RFC3951.
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*
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* Original code Copyright (C) The Internet Society (2004).
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* All changes to produce this version Copyright (C) 2008 by Steve Underwood
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* All Rights Reserved.
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*
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* This program is distributed in the hope that it will be useful,
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* but WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
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*
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* $Id: anaFilter.c,v 1.2 2008/03/06 12:27:37 steveu Exp $
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*/
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/*! \file */
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#ifdef HAVE_CONFIG_H
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#include <config.h>
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#endif
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#include <inttypes.h>
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#include <string.h>
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#include "anaFilter.h"
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#include "ilbc.h"
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/*----------------------------------------------------------------*
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* LP analysis filter.
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*---------------------------------------------------------------*/
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void anaFilter(float *In, /* (i) Signal to be filtered */
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float *a, /* (i) LP parameters */
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int len, /* (i) Length of signal */
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float *Out, /* (o) Filtered signal */
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float *mem) /* (i/o) Filter state */
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{
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int i;
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int j;
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float *po;
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float *pi;
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float *pm;
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float *pa;
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po = Out;
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/* Filter first part using memory from past */
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for (i = 0; i < ILBC_LPC_FILTERORDER; i++)
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{
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pi = &In[i];
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pm = &mem[ILBC_LPC_FILTERORDER - 1];
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pa = a;
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*po = 0.0;
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for (j = 0; j <= i; j++)
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*po += (*pa++)*(*pi--);
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for (j = i + 1; j < ILBC_LPC_FILTERORDER + 1; j++)
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*po += (*pa++)*(*pm--);
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po++;
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}
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/* Filter last part where the state is entirely
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in the input vector */
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for (i = ILBC_LPC_FILTERORDER; i < len; i++)
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{
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pi = &In[i];
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pa = a;
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*po = 0.0;
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for (j = 0; j < ILBC_LPC_FILTERORDER + 1; j++)
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*po += (*pa++)*(*pi--);
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po++;
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}
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/* Update state vector */
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memcpy(mem, &In[len - ILBC_LPC_FILTERORDER], ILBC_LPC_FILTERORDER*sizeof(float));
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}
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