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