asterisk/codecs/ilbc/anaFilter.c

 
/****************************************************************** 
 
    iLBC Speech Coder ANSI-C Source Code 
 
    anaFilter.c  
 
    Copyright (c) 2001, 
    Global IP Sound AB. 
    All rights reserved. 
 
******************************************************************/ 
 
#include <string.h> 
#include "iLBC_define.h" 
#include "anaFilter.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 entierly  
       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)); 
}