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