git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@7221 65c4cc65-6c06-0410-ace0-fbb531ad65f3
169 lines
5.2 KiB
C
169 lines
5.2 KiB
C
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/******************************************************************
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iLBC Speech Coder ANSI-C Source Code
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filter.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 "filter.h"
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/*----------------------------------------------------------------*
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* all-pole filter
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*---------------------------------------------------------------*/
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void AllPoleFilter(
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float *InOut, /* (i/o) on entrance InOut[-orderCoef] to
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InOut[-1] contain the state of the
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filter (delayed samples). InOut[0] to
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InOut[lengthInOut-1] contain the filter
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input, on en exit InOut[-orderCoef] to
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InOut[-1] is unchanged and InOut[0] to
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InOut[lengthInOut-1] contain filtered
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samples */
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float *Coef,/* (i) filter coefficients, Coef[0] is assumed
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to be 1.0 */
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int lengthInOut,/* (i) number of input/output samples */
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int orderCoef /* (i) number of filter coefficients */
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){
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int n,k;
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for(n=0;n<lengthInOut;n++){
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for(k=1;k<=orderCoef;k++){
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*InOut -= Coef[k]*InOut[-k];
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}
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InOut++;
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}
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}
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/*----------------------------------------------------------------*
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* all-zero filter
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*---------------------------------------------------------------*/
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void AllZeroFilter(
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float *In, /* (i) In[0] to In[lengthInOut-1] contain
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filter input samples */
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float *Coef,/* (i) filter coefficients (Coef[0] is assumed
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to be 1.0) */
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int lengthInOut,/* (i) number of input/output samples */
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int orderCoef, /* (i) number of filter coefficients */
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float *Out /* (i/o) on entrance Out[-orderCoef] to Out[-1]
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contain the filter state, on exit Out[0]
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to Out[lengthInOut-1] contain filtered
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samples */
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){
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int n,k;
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for(n=0;n<lengthInOut;n++){
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*Out = Coef[0]*In[0];
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for(k=1;k<=orderCoef;k++){
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*Out += Coef[k]*In[-k];
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}
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Out++;
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In++;
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}
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}
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/*----------------------------------------------------------------*
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* pole-zero filter
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*---------------------------------------------------------------*/
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void ZeroPoleFilter(
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float *In, /* (i) In[0] to In[lengthInOut-1] contain
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filter input samples In[-orderCoef] to
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In[-1] contain state of all-zero
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section */
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float *ZeroCoef,/* (i) filter coefficients for all-zero
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section (ZeroCoef[0] is assumed to
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be 1.0) */
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float *PoleCoef,/* (i) filter coefficients for all-pole section
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(ZeroCoef[0] is assumed to be 1.0) */
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int lengthInOut,/* (i) number of input/output samples */
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int orderCoef, /* (i) number of filter coefficients */
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float *Out /* (i/o) on entrance Out[-orderCoef] to Out[-1]
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contain state of all-pole section. On
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exit Out[0] to Out[lengthInOut-1]
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contain filtered samples */
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){
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AllZeroFilter(In,ZeroCoef,lengthInOut,orderCoef,Out);
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AllPoleFilter(Out,PoleCoef,lengthInOut,orderCoef);
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}
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/*----------------------------------------------------------------*
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* downsample (LP filter and decimation)
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*---------------------------------------------------------------*/
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void DownSample (
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float *In, /* (i) input samples */
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float *Coef, /* (i) filter coefficients */
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int lengthIn, /* (i) number of input samples */
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float *state, /* (i) filter state */
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float *Out /* (o) downsampled output */
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){
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float o;
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float *Out_ptr = Out;
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float *Coef_ptr, *In_ptr;
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float *state_ptr;
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int i, j, stop;
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/* LP filter and decimate at the same time */
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for (i = DELAY_DS; i < lengthIn; i+=FACTOR_DS)
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{
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Coef_ptr = &Coef[0];
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In_ptr = &In[i];
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state_ptr = &state[FILTERORDER_DS-2];
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o = (float)0.0;
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stop = (i < FILTERORDER_DS) ? i + 1 : FILTERORDER_DS;
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for (j = 0; j < stop; j++)
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{
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o += *Coef_ptr++ * (*In_ptr--);
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}
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for (j = i + 1; j < FILTERORDER_DS; j++)
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{
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o += *Coef_ptr++ * (*state_ptr--);
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}
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*Out_ptr++ = o;
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}
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/* Get the last part (use zeros as input for the future) */
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for (i=(lengthIn+FACTOR_DS); i<(lengthIn+DELAY_DS);
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i+=FACTOR_DS) {
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o=(float)0.0;
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if (i<lengthIn) {
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Coef_ptr = &Coef[0];
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In_ptr = &In[i];
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for (j=0; j<FILTERORDER_DS; j++) {
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o += *Coef_ptr++ * (*Out_ptr--);
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}
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} else {
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Coef_ptr = &Coef[i-lengthIn];
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In_ptr = &In[lengthIn-1];
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for (j=0; j<FILTERORDER_DS-(i-lengthIn); j++) {
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o += *Coef_ptr++ * (*In_ptr--);
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}
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}
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*Out_ptr++ = o;
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}
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}
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