annotate libtwamr/lsfwt.c @ 485:751f06541fbb

doc/Codec-utils: clarify lack of DHF in gsmfr-decode-rb
author Mychaela Falconia <falcon@freecalypso.org>
date Mon, 20 May 2024 01:47:22 +0000
parents 8861f41e4507
children
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1 /*
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2 ********************************************************************************
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3 *
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4 * GSM AMR-NB speech codec R98 Version 7.6.0 December 12, 2001
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5 * R99 Version 3.3.0
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6 * REL-4 Version 4.1.0
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7 *
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8 ********************************************************************************
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9 *
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10 * File : lsfwt.c
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11 * Purpose : Compute LSF weighting factors
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12 *
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13 ********************************************************************************
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14 */
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15
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16 /*
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17 ********************************************************************************
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18 * MODULE INCLUDE FILE AND VERSION ID
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19 ********************************************************************************
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20 */
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21 #include "namespace.h"
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22 #include "lsfwt.h"
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23
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24 /*
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25 ********************************************************************************
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26 * INCLUDE FILES
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27 ********************************************************************************
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28 */
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29 #include "typedef.h"
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30 #include "basic_op.h"
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31 #include "no_count.h"
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32 #include "cnst.h"
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33
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34 /*
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35 ********************************************************************************
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36 * PUBLIC PROGRAM CODE
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37 ********************************************************************************
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38 */
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39 /****************************************************
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40 *
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41 * FUNCTION Lsf_wt *
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42 * *
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43 ****************************************************
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44 * Compute LSF weighting factors *
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45 * *
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46 * d[i] = lsf[i+1] - lsf[i-1] *
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47 * *
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48 * The weighting factors are approximated by two line segment. *
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49 * *
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50 * First segment passes by the following 2 points: *
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51 * *
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52 * d[i] = 0Hz wf[i] = 3.347 *
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53 * d[i] = 450Hz wf[i] = 1.8 *
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54 * *
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55 * Second segment passes by the following 2 points: *
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56 * *
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57 * d[i] = 450Hz wf[i] = 1.8 *
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58 * d[i] = 1500Hz wf[i] = 1.0 *
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59 * *
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60 * if( d[i] < 450Hz ) *
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61 * wf[i] = 3.347 - ( (3.347-1.8) / (450-0)) * d[i] *
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62 * else *
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63 * wf[i] = 1.8 - ( (1.8-1.0) / (1500-450)) * (d[i] - 450) *
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64 * *
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65 * *
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66 * if( d[i] < 1843) *
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67 * wf[i] = 3427 - (28160*d[i])>>15 *
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68 * else *
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69 * wf[i] = 1843 - (6242*(d[i]-1843))>>15 *
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70 * *
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71 *--------------------------------------------------------------------------*/
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72
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73 void Lsf_wt (
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74 Word16 *lsf, /* input : LSF vector */
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75 Word16 *wf) /* output: square of weighting factors */
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76 {
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77 Word16 temp;
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78 Word16 i;
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79 /* wf[0] = lsf[1] - 0 */
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80 wf[0] = lsf[1]; move16 ();
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81 for (i = 1; i < 9; i++)
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82 {
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83 wf[i] = sub (lsf[i + 1], lsf[i - 1]); move16 ();
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84 }
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85 /* wf[9] = 0.5 - lsf[8] */
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86 wf[9] = sub (16384, lsf[8]);move16 ();
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87
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88 for (i = 0; i < 10; i++)
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89 {
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90 temp = sub (wf[i], 1843);
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91 test ();
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92 if (temp < 0)
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93 {
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94 wf[i] = sub (3427, mult (wf[i], 28160)); move16 ();
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95 }
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96 else
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97 {
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98 wf[i] = sub (1843, mult (temp, 6242)); move16 ();
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99 }
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100
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101 wf[i] = shl (wf[i], 3); move16 ();
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102 }
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103 return;
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104 }