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annotate libtwamr/enc_lag6.c @ 553:ebcf414b7d99

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doc/TFO-transform: describe details for FRv1, both modes
author Mychaela Falconia <falcon@freecalypso.org>
date Mon, 07 Oct 2024 08:24:24 +0000
parents 0349de7c45b7
children
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0349de7c45b7 libtwamr: integrate enc_lag[36].c
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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 : enc_lag6.c
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11 * Purpose : Encoding of fractional pitch lag with 1/6 resolution.
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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 * MODULE INCLUDE FILE AND VERSION ID
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18 ********************************************************************************
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19 */
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20 #include "namespace.h"
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21 #include "enc_lag6.h"
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22
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23 /*
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24 ********************************************************************************
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25 * INCLUDE FILES
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26 ********************************************************************************
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27 */
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28 #include "typedef.h"
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29 #include "basic_op.h"
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30 #include "no_count.h"
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31
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32 /*
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33 ********************************************************************************
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34 * LOCAL VARIABLES AND TABLES
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35 ********************************************************************************
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36 */
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37
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38 /*
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39 ********************************************************************************
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40 * PUBLIC PROGRAM CODE
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41 ********************************************************************************
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42 */
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43 /*************************************************************************
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44 *
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45 * FUNCTION: Enc_lag6
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46 *
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47 * PURPOSE: Encoding of fractional pitch lag with 1/6 resolution.
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48 *
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49 * DESCRIPTION:
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50 * First and third subframes:
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51 * --------------------------
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52 * The pitch range is divided as follows:
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53 * 17 3/6 to 94 3/6 resolution 1/6
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54 * 95 to 143 resolution 1
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55 *
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56 * The period is encoded with 9 bits.
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57 * For the range with fractions:
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58 * index = (T-17)*6 + frac - 3;
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59 * where T=[17..94] and frac=[-2,-1,0,1,2,3]
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60 * and for the integer only range
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61 * index = (T - 95) + 463; where T=[95..143]
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62 *
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63 * Second and fourth subframes:
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64 * ----------------------------
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65 * For the 2nd and 4th subframes a resolution of 1/6 is always used,
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66 * and the search range is relative to the lag in previous subframe.
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67 * If t0 is the lag in the previous subframe then
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68 * t_min=t0-5 and t_max=t0+4 and the range is given by
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69 * (t_min-1) 3/6 to (t_max) 3/6
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70 *
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71 * The period in the 2nd (and 4th) subframe is encoded with 6 bits:
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72 * index = (T-(t_min-1))*6 + frac - 3;
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73 * where T=[t_min-1..t_max] and frac=[-2,-1,0,1,2,3]
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74 *
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75 * Note that only 61 values are used. If the decoder receives 61, 62,
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76 * or 63 as the relative pitch index, it means that a transmission
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77 * error occurred and the pitch from previous subframe should be used.
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78 *
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79 *************************************************************************/
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80 Word16 Enc_lag6 ( /* o : Return index of encoding */
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81 Word16 T0, /* i : Pitch delay */
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82 Word16 T0_frac, /* i : Fractional pitch delay */
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83 Word16 T0_min, /* i : minimum of search range */
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84 Word16 delta_flag /* i : Flag for 1st (or 3rd) subframe */
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85 )
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86 {
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87 Word16 index, i;
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88
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89 test ();
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90 if (delta_flag == 0) /* if 1st or 3rd subframe */
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91 {
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92 /* encode pitch delay (with fraction) */
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93 test ();
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94 if (sub (T0, 94) <= 0)
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95 {
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96 /* index = T0*6 - 105 + T0_frac */
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97 i = add (add (T0, T0), T0);
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98 index = add (sub (add (i, i), 105), T0_frac);
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99 }
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100 else
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101 {
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102 index = add (T0, 368);
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103 }
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104
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105 }
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106 else
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107 /* if second or fourth subframe */
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108 {
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109 /* index = 6*(T0-T0_min) + 3 + T0_frac */
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110 i = sub (T0, T0_min);
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111 i = add (add (i, i), i);
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112 index = add (add (add (i, i), 3), T0_frac);
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113 }
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114
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115 return index;
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116 }