FreeCalypso > hg > gsm-codec-lib
annotate libtwamr/enc_lag6.c @ 449:2af2b5c12268
Library-versions: libtwamr is officially version 1.0.0
author | Mychaela Falconia <falcon@freecalypso.org> |
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date | Fri, 10 May 2024 01:43:05 +0000 |
parents | 0349de7c45b7 |
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rev | line source |
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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 } |