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annotate src/dec_lag6.c @ 2:c511bfb36c2a

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beginning of EFR2 decoder, using AMR version of AGC module
author Mychaela Falconia <falcon@freecalypso.org>
date Wed, 03 Apr 2024 05:47:51 +0000
parents 56410792419a
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 "typedef.h"
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20 #include "basic_op.h"
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21 #include "count.h"
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22
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23 /* Old integer lag */
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24
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25 Word16 old_T0;
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26
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27 Word16
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28 Dec_lag6 ( /* output: return integer pitch lag */
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29 Word16 index, /* input : received pitch index */
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30 Word16 pit_min, /* input : minimum pitch lag */
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31 Word16 pit_max, /* input : maximum pitch lag */
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32 Word16 i_subfr, /* input : subframe flag */
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33 Word16 L_frame_by2,/* input : speech frame size divided by 2 */
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34 Word16 *T0_frac, /* output: fractional part of pitch lag */
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35 Word16 bfi /* input : bad frame indicator */
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36 )
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37 {
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38 Word16 pit_flag;
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39 Word16 T0, i;
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40 static Word16 T0_min, T0_max;
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41
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42 pit_flag = i_subfr; move16 (); /* flag for 1st or 3rd subframe */
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43 test ();
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44 if (sub (i_subfr, L_frame_by2) == 0)
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45 {
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46 pit_flag = 0; move16 ();
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47 }
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48 test ();
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49 if (pit_flag == 0) /* if 1st or 3rd subframe */
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50 {
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51 test ();
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52 if (bfi == 0)
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53 { /* if bfi == 0 decode pitch */
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54 test ();
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55 if (sub (index, 463) < 0)
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56 {
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57 /* T0 = (index+5)/6 + 17 */
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58 T0 = add (mult (add (index, 5), 5462), 17);
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59 i = add (add (T0, T0), T0);
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60 /* *T0_frac = index - T0*6 + 105 */
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61 *T0_frac = add (sub (index, add (i, i)), 105);
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62 move16 ();
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63 }
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64 else
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65 {
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66 T0 = sub (index, 368);
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67 *T0_frac = 0; move16 ();
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68 }
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69 }
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70 else
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71 /* bfi == 1 */
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72 {
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73 T0 = old_T0; move16 ();
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74 *T0_frac = 0; move16 ();
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75 }
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76
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77 /* find T0_min and T0_max for 2nd (or 4th) subframe */
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78
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79 T0_min = sub (T0, 5);
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80 test ();
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81 if (sub (T0_min, pit_min) < 0)
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82 {
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83 T0_min = pit_min; move16 ();
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84 }
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85 T0_max = add (T0_min, 9);
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86 test ();
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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; move16 ();
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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 move16 ();
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106 }
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107 else
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108 /* bfi == 1 OR index >= 61 */
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109 {
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110 T0 = old_T0; move16 ();
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111 *T0_frac = 0; move16 ();
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112 }
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113 }
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114
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115 old_T0 = T0; move16 ();
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116
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117 return T0;
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118 }