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