FreeCalypso > hg > gsm-codec-lib

annotate libgsmefr/dec_lag6.c @ 303:4034c2b06ec8

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doc/FR1-Rx-DTX: update for libgsmfr2 and the new landscape
author Mychaela Falconia <falcon@freecalypso.org>
date Mon, 15 Apr 2024 22:07:00 +0000
parents f387ee919f2c
children
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1 /*************************************************************************
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2 * FUNCTION: Dec_lag6
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3 *
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4 * PURPOSE: Decoding of fractional pitch lag with 1/6 resolution.
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5 * Extract the integer and fraction parts of the pitch lag from
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6 * the received adaptive codebook index.
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7 *
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8 * See "Enc_lag6.c" for more details about the encoding procedure.
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9 *
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10 * The fractional lag in 1st and 3rd subframes is encoded with 9 bits
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11 * while that in 2nd and 4th subframes is relatively encoded with 6 bits.
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12 * Note that in relative encoding only 61 values are used. If the
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13 * decoder receives 61, 62, or 63 as the relative pitch index, it means
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14 * that a transmission error occurred. In this case, the pitch lag from
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15 * previous subframe is used.
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16 *
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17 *************************************************************************/
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18
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19 #include "gsm_efr.h"
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20 #include "typedef.h"
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21 #include "namespace.h"
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22 #include "basic_op.h"
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23 #include "no_count.h"
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24 #include "codec.h"
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25 #include "cnst.h"
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26 #include "dec_state.h"
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27
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28 Word16 Dec_lag6 ( /* output: return integer pitch lag */
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29 struct EFR_decoder_state *st,
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30 Word16 index, /* input : received pitch index */
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31 Word16 pit_min, /* input : minimum pitch lag */
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32 Word16 pit_max, /* input : maximum pitch lag */
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33 Word16 i_subfr, /* input : subframe flag */
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34 Word16 L_frame_by2,/* input : speech frame size divided by 2 */
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35 Word16 *T0_frac, /* output: fractional part of pitch lag */
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36 Word16 bfi, /* input : bad frame indicator */
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37 Word16 *T0_min,
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38 Word16 *T0_max
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39 )
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40 {
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41 Word16 pit_flag;
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42 Word16 T0, i;
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43
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44 pit_flag = i_subfr; move16 (); /* flag for 1st or 3rd subframe */
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45 test ();
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46 if (i_subfr == L_frame_by2)
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47 {
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48 pit_flag = 0; move16 ();
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49 }
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50 test ();
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51 if (pit_flag == 0) /* if 1st or 3rd subframe */
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52 {
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53 test ();
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54 if (bfi == 0)
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55 { /* if bfi == 0 decode pitch */
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56 test ();
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57 if (index < 463)
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58 {
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59 /* T0 = (index+5)/6 + 17 */
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60 T0 = add (mult (add (index, 5), 5462), 17);
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61 i = add (add (T0, T0), T0);
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62 /* *T0_frac = index - T0*6 + 105 */
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63 *T0_frac = add (sub (index, add (i, i)), 105);
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64 move16 ();
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65 }
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66 else
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67 {
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68 T0 = index - 368;
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69 *T0_frac = 0; move16 ();
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70 }
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71 }
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72 else
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73 /* bfi == 1 */
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74 {
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75 T0 = st->old_T0;
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76 *T0_frac = 0;
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77 }
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78
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79 /* find T0_min and T0_max for 2nd (or 4th) subframe */
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80
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81 *T0_min = sub (T0, 5);
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82 if (*T0_min < pit_min)
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83 {
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84 *T0_min = pit_min;
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85 }
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86 *T0_max = add (*T0_min, 9);
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87 if (*T0_max > pit_max)
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88 {
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89 *T0_max = pit_max;
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90 *T0_min = sub (*T0_max, 9);
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91 }
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92 }
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93 else
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94 /* second or fourth subframe */
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95 {
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96 test (); test ();
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97 /* if bfi == 0 decode pitch */
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98 if ((bfi == 0) && (index < 61))
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99 {
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100 /* i = (index+5)/6 - 1 */
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101 i = sub (mult (add (index, 5), 5462), 1);
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102 T0 = add (i, *T0_min);
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103 i = add (add (i, i), i);
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104 *T0_frac = sub (sub (index, 3), add (i, i));
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105 }
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106 else
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107 /* bfi == 1 OR index >= 61 */
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108 {
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109 T0 = st->old_T0;
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110 *T0_frac = 0;
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111 }
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112 }
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113
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114 st->old_T0 = T0;
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115
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116 return T0;
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117 }