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annotate libtwamr/dec_lag6.c @ 485:751f06541fbb

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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 7bea058d0640
children
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7bea058d0640 libtwamr: integrate dec_lag6.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 : dec_lag6.c
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11 * Purpose : Decoding 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 /*
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18 ********************************************************************************
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19 * MODULE INCLUDE FILE AND VERSION ID
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20 ********************************************************************************
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21 */
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22 #include "namespace.h"
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23 #include "dec_lag6.h"
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24
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25 /*
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26 ********************************************************************************
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27 * INCLUDE FILES
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28 ********************************************************************************
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29 */
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30 #include "typedef.h"
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31 #include "basic_op.h"
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32 #include "no_count.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: Dec_lag6
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42 *
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43 * PURPOSE: Decoding of fractional pitch lag with 1/6 resolution.
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44 * Extract the integer and fraction parts of the pitch lag from
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45 * the received adaptive codebook index.
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46 *
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47 * See "Enc_lag6.c" for more details about the encoding procedure.
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48 *
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49 * The fractional lag in 1st and 3rd subframes is encoded with 9 bits
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50 * while that in 2nd and 4th subframes is relatively encoded with 6 bits.
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51 * Note that in relative encoding only 61 values are used. If the
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52 * decoder receives 61, 62, or 63 as the relative pitch index, it means
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53 * that a transmission error occurred. In this case, the pitch lag from
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54 * previous subframe (actually from previous frame) is used.
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55 *
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56 ************************************************************************
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57 */
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58 void Dec_lag6 (
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59 Word16 index, /* input : received pitch index */
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60 Word16 pit_min, /* input : minimum pitch lag */
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61 Word16 pit_max, /* input : maximum pitch lag */
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62 Word16 i_subfr, /* input : subframe flag */
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63 Word16 *T0, /* in/out: integer part of pitch lag */
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64 Word16 *T0_frac /* output: fractional part of pitch lag */
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65 )
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66 {
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67 Word16 i;
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68 Word16 T0_min, T0_max;
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69
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70 test ();
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71 if (i_subfr == 0) /* if 1st or 3rd subframe */
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72 {
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73 test ();
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74 if (sub (index, 463) < 0)
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75 {
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76 /* T0 = (index+5)/6 + 17 */
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77 *T0 = add (mult (add (index, 5), 5462), 17);
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78 i = add (add (*T0, *T0), *T0);
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79 /* *T0_frac = index - T0*6 + 105 */
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80 *T0_frac = add (sub (index, add (i, i)), 105);
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81 move16 ();
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82 }
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83 else
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84 {
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85 *T0 = sub (index, 368);
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86 *T0_frac = 0; move16 ();
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87 }
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88 }
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89 else
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90 /* second or fourth subframe */
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91 {
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92 /* find T0_min and T0_max for 2nd (or 4th) subframe */
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93
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94 T0_min = sub (*T0, 5);
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95
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96 test ();
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97 if (sub (T0_min, pit_min) < 0)
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98 {
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99 T0_min = pit_min; move16 ();
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100 }
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101 T0_max = add (T0_min, 9);
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102
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103 test ();
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104 if (sub (T0_max, pit_max) > 0)
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105 {
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106 T0_max = pit_max; move16 ();
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107 T0_min = sub (T0_max, 9);
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108 }
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109
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110 /* i = (index+5)/6 - 1 */
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111 i = sub (mult (add (index, 5), 5462), 1);
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112 *T0 = add (i, T0_min);
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113 i = add (add (i, i), i);
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114 *T0_frac = sub (sub (index, 3), add (i, i));
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115 move16 ();
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116 }
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117 }