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/******************************************************************
iLBC Speech Coder ANSI-C Source Code
anaFilter.c
Copyright (C) The Internet Society (2004).
All Rights Reserved.
******************************************************************/
#include <string.h>
#include "iLBC_define.h"
/*----------------------------------------------------------------*
* LP analysis filter.
*---------------------------------------------------------------*/
void anaFilter(
float *In, /* (i) Signal to be filtered */
float *a, /* (i) LP parameters */
int len,/* (i) Length of signal */
float *Out, /* (o) Filtered signal */
float *mem /* (i/o) Filter state */
){
int i, j;
float *po, *pi, *pm, *pa;
po = Out;
/* Filter first part using memory from past */
for (i=0; i<LPC_FILTERORDER; i++) {
pi = &In[i];
pm = &mem[LPC_FILTERORDER-1];
pa = a;
*po=0.0;
for (j=0; j<=i; j++) {
*po+=(*pa++)*(*pi--);
}
for (j=i+1; j<LPC_FILTERORDER+1; j++) {
*po+=(*pa++)*(*pm--);
}
po++;
}
/* Filter last part where the state is entirely
in the input vector */
for (i=LPC_FILTERORDER; i<len; i++) {
pi = &In[i];
pa = a;
*po=0.0;
for (j=0; j<LPC_FILTERORDER+1; j++) {
*po+=(*pa++)*(*pi--);
}
po++;
}
/* Update state vector */
memcpy(mem, &In[len-LPC_FILTERORDER],
LPC_FILTERORDER*sizeof(float));
}
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