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1
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2 /******************************************************************
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3
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4 iLBC Speech Coder ANSI-C Source Code
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5
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6 syntFilter.c
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7
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8 Copyright (C) The Internet Society (2004).
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9 All Rights Reserved.
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10
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11 ******************************************************************/
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12
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13 #include "iLBC_define.h"
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14
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15 /*----------------------------------------------------------------*
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16 * LP synthesis filter.
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17 *---------------------------------------------------------------*/
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18
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19 void syntFilter(float *Out, /* (i/o) Signal to be filtered */
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20 float *a, /* (i) LP parameters */
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21 int len, /* (i) Length of signal */
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22 float *mem /* (i/o) Filter state */
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23 )
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24 {
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25 int i, j;
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26 float *po, *pi, *pa, *pm;
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27
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28 po = Out;
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29
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30 /* Filter first part using memory from past */
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31
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32 for (i = 0; i < LPC_FILTERORDER; i++) {
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33 pi = &Out[i - 1];
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34 pa = &a[1];
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35 pm = &mem[LPC_FILTERORDER - 1];
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36 for (j = 1; j <= i; j++) {
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37 *po -= (*pa++) * (*pi--);
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38 }
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39 for (j = i + 1; j < LPC_FILTERORDER + 1; j++) {
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40 *po -= (*pa++) * (*pm--);
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41 }
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42 po++;
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43 }
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44
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45 /* Filter last part where the state is entirely in
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46 the output vector */
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47
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48 for (i = LPC_FILTERORDER; i < len; i++) {
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49 pi = &Out[i - 1];
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50 pa = &a[1];
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51 for (j = 1; j < LPC_FILTERORDER + 1; j++) {
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52 *po -= (*pa++) * (*pi--);
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53 }
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54 po++;
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55 }
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56
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57 /* Update state vector */
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58
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59 memcpy(mem, &Out[len - LPC_FILTERORDER],
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60 LPC_FILTERORDER * sizeof(float));
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61 }
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