/****************************************************************** | |
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)); | |
} | |