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annotate src/autocorr.c @ 5:799b56cbccb6

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EFR2 decoder: add post-processing step from AMR
author Mychaela Falconia <falcon@freecalypso.org>
date Wed, 03 Apr 2024 06:09:10 +0000
parents 56410792419a
children
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1 /*************************************************************************
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2 *
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3 * FUNCTION: autocorr
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4 *
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5 * PURPOSE: Compute autocorrelations of signal with windowing
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6 *
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7 * DESCRIPTION:
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8 * - Windowing of input speech: s'[n] = s[n] * w[n]
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9 * - Autocorrelations of input speech:
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10 * r[k] = sum_{i=k}^{239} s'[i]*s'[i-k] k=0,...,10
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11 * The autocorrelations are expressed in normalized double precision
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12 * format.
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13 *
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14 *************************************************************************/
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15
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16 #include "typedef.h"
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17 #include "basic_op.h"
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18 #include "oper_32b.h"
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19 #include "count.h"
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20 #include "cnst.h"
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21
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22 Word16 Autocorr (
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23 Word16 x[], /* (i) : Input signal */
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24 Word16 m, /* (i) : LPC order */
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25 Word16 r_h[], /* (o) : Autocorrelations (msb) */
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26 Word16 r_l[], /* (o) : Autocorrelations (lsb) */
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27 Word16 wind[] /* (i) : window for LPC analysis */
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28 )
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29 {
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30 Word16 i, j, norm;
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31 Word16 y[L_WINDOW];
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32 Word32 sum;
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33 Word16 overfl, overfl_shft;
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34
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35 /* Windowing of signal */
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36
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37 for (i = 0; i < L_WINDOW; i++)
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38 {
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39 y[i] = mult_r (x[i], wind[i]); move16 ();
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40 }
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41
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42 /* Compute r[0] and test for overflow */
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43
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44 overfl_shft = 0; move16 ();
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45
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46 do
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47 {
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48 overfl = 0; move16 ();
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49 sum = 0L; move32 ();
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50
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51 for (i = 0; i < L_WINDOW; i++)
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52 {
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53 sum = L_mac (sum, y[i], y[i]);
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54 }
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55
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56 /* If overflow divide y[] by 4 */
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57
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58 test ();
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59 if (L_sub (sum, MAX_32) == 0L)
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60 {
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61 overfl_shft = add (overfl_shft, 4);
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62 overfl = 1; move16 (); /* Set the overflow flag */
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63
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64 for (i = 0; i < L_WINDOW; i++)
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65 {
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66 y[i] = shr (y[i], 2); move16 ();
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67 }
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68 }
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69 test ();
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70 }
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71 while (overfl != 0);
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72
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73 sum = L_add (sum, 1L); /* Avoid the case of all zeros */
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74
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75 /* Normalization of r[0] */
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76
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77 norm = norm_l (sum);
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78 sum = L_shl (sum, norm);
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79 L_Extract (sum, &r_h[0], &r_l[0]); /* Put in DPF format (see oper_32b) */
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80
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81 /* r[1] to r[m] */
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82
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83 for (i = 1; i <= m; i++)
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84 {
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85 sum = 0; move32 ();
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86
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87 for (j = 0; j < L_WINDOW - i; j++)
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88 {
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89 sum = L_mac (sum, y[j], y[j + i]);
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90 }
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91
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92 sum = L_shl (sum, norm);
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93 L_Extract (sum, &r_h[i], &r_l[i]);
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94 }
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95
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96 norm = sub (norm, overfl_shft);
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97
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98 return norm;
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99 }