anaFilter.c

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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));
 }