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annotate libgsmefr/dec_lag6.c @ 183:452c1d5a6268

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libgsmefr BFI w/o data: emit zero output after decoder reset In real-life usage, each EFR decoder session will most likely begin with lots of BFI frames before the first real frame arrives. However, because the spec-defined home state of the decoder is speech rather than CN, our regular logic for BFI w/o data would have to feed pseudorandom noise to the decoder (in the "fixed codebook excitation pulses" part), which is silly to do at the beginning of the decoder session right out of reset. Therefore, let's check reset_flag_old, and if we are still in the reset state, simply emit zero output.
author Mychaela Falconia <falcon@freecalypso.org>
date Tue, 03 Jan 2023 00:12:18 +0000
parents cb080ec1817e
children f387ee919f2c
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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 (sub (i_subfr, L_frame_by2) == 0)
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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 (sub (index, 463) < 0)
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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 = sub (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 (sub (*T0_min, pit_min) < 0)
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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 (sub (*T0_max, pit_max) > 0)
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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) && (sub (index, 61) < 0))
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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 }