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annotate libgsmefr/pre_proc.c @ 53:49dd1ac8e75b

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libgsmefr: import most *.c files from ETSI source
author Mychaela Falconia <falcon@freecalypso.org>
date Fri, 25 Nov 2022 16:18:21 +0000
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children 3ea19a9aa2a1
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1 /*************************************************************************
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2 *
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3 * FUNCTION: Pre_Process()
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4 *
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5 * PURPOSE: Preprocessing of input speech.
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6 *
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7 * DESCRIPTION:
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8 * - 2nd order high pass filtering with cut off frequency at 80 Hz.
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9 * - Divide input by two.
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10 *
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11 *************************************************************************/
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12
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13 #include "typedef.h"
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14 #include "basic_op.h"
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15 #include "oper_32b.h"
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16 #include "count.h"
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17
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18 /*------------------------------------------------------------------------*
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19 * *
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20 * Algorithm: *
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21 * *
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22 * y[i] = b[0]*x[i]/2 + b[1]*x[i-1]/2 + b[2]*x[i-2]/2 *
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23 * + a[1]*y[i-1] + a[2]*y[i-2]; *
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24 * *
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25 * *
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26 * Input is divided by two in the filtering process. *
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27 *------------------------------------------------------------------------*/
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28
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29 /* filter coefficients (fc = 80 Hz, coeff. b[] is divided by 2) */
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30
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31 static const Word16 b[3] = {1899, -3798, 1899};
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32 static const Word16 a[3] = {4096, 7807, -3733};
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33
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34 /* Static values to be preserved between calls */
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35 /* y[] values are kept in double precision */
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36
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37 static Word16 y2_hi, y2_lo, y1_hi, y1_lo, x0, x1;
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38
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39 /* Initialization of static values */
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40
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41 void Init_Pre_Process (void)
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42 {
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43 y2_hi = 0;
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44 y2_lo = 0;
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45 y1_hi = 0;
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46 y1_lo = 0;
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47 x0 = 0;
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48 x1 = 0;
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49 }
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50
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51 void Pre_Process (
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52 Word16 signal[], /* input/output signal */
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53 Word16 lg) /* lenght of signal */
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54 {
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55 Word16 i, x2;
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56 Word32 L_tmp;
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57
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58 for (i = 0; i < lg; i++)
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59 {
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60 x2 = x1; move16 ();
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61 x1 = x0; move16 ();
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62 x0 = signal[i]; move16 ();
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63
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64 /* y[i] = b[0]*x[i]/2 + b[1]*x[i-1]/2 + b140[2]*x[i-2]/2 */
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65 /* + a[1]*y[i-1] + a[2] * y[i-2]; */
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66
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67 L_tmp = Mpy_32_16 (y1_hi, y1_lo, a[1]);
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68 L_tmp = L_add (L_tmp, Mpy_32_16 (y2_hi, y2_lo, a[2]));
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69 L_tmp = L_mac (L_tmp, x0, b[0]);
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70 L_tmp = L_mac (L_tmp, x1, b[1]);
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71 L_tmp = L_mac (L_tmp, x2, b[2]);
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72 L_tmp = L_shl (L_tmp, 3);
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73 signal[i] = round (L_tmp); move16 ();
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74
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75 y2_hi = y1_hi; move16 ();
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76 y2_lo = y1_lo; move16 ();
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77 L_Extract (L_tmp, &y1_hi, &y1_lo);
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78 }
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79 return;
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80 }