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annotate libgsmfr2/long_term.c @ 478:936a08cc73ce

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doc/AMR-library-API: describe the decoder
author Mychaela Falconia <falcon@freecalypso.org>
date Sun, 19 May 2024 21:32:31 +0000
parents 65d3304502bd
children
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1 /*
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2 * This C source file has been adapted from TU-Berlin libgsm source,
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3 * original notice follows:
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4 *
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5 * Copyright 1992 by Jutta Degener and Carsten Bormann, Technische
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6 * Universitaet Berlin. See the accompanying file "COPYRIGHT" for
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7 * details. THERE IS ABSOLUTELY NO WARRANTY FOR THIS SOFTWARE.
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8 */
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9
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10 #include <stdint.h>
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11 #include <assert.h>
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12 #include "tw_gsmfr.h"
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13 #include "typedef.h"
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14 #include "ed_state.h"
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15 #include "ed_internal.h"
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16
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17 /*
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18 * 4.2.11 .. 4.2.12 LONG TERM PREDICTOR (LTP) SECTION
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19 */
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20
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21
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22 /*
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23 * This module computes the LTP gain (bc) and the LTP lag (Nc)
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24 * for the long term analysis filter. This is done by calculating a
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25 * maximum of the cross-correlation function between the current
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26 * sub-segment short term residual signal d[0..39] (output of
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27 * the short term analysis filter; for simplification the index
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28 * of this array begins at 0 and ends at 39 for each sub-segment of the
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29 * RPE-LTP analysis) and the previous reconstructed short term
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30 * residual signal dp[ -120 .. -1 ]. A dynamic scaling must be
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31 * performed to avoid overflow.
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32 */
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33
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34 static void Calculation_of_the_LTP_parameters (
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35 register word * d, /* [0..39] IN */
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36 register word * dp, /* [-120..-1] IN */
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37 word * bc_out, /* OUT */
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38 word * Nc_out /* OUT */
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39 )
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40 {
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41 register int k, lambda;
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42 word Nc, bc;
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43 word wt[40];
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44
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45 longword L_max, L_power;
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46 word R, S, dmax, scal;
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47 register word temp;
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48
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49 /* Search of the optimum scaling of d[0..39].
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50 */
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51 dmax = 0;
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52
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53 for (k = 0; k <= 39; k++) {
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54 temp = d[k];
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55 temp = GSM_ABS( temp );
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56 if (temp > dmax) dmax = temp;
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57 }
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58
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59 temp = 0;
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60 if (dmax == 0) scal = 0;
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61 else {
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62 assert(dmax > 0);
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63 temp = gsm_norm( (longword)dmax << 16 );
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64 }
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65
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66 if (temp > 6) scal = 0;
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67 else scal = 6 - temp;
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68
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69 assert(scal >= 0);
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70
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71 /* Initialization of a working array wt
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72 */
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73
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74 for (k = 0; k <= 39; k++) wt[k] = SASR( d[k], scal );
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75
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76 /* Search for the maximum cross-correlation and coding of the LTP lag
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77 */
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78 L_max = 0;
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79 Nc = 40; /* index for the maximum cross-correlation */
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80
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81 for (lambda = 40; lambda <= 120; lambda++) {
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82
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83 # undef STEP
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84 # define STEP(k) (longword)wt[k] * dp[k - lambda]
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85
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86 register longword L_result;
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87
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88 L_result = STEP(0) ; L_result += STEP(1) ;
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89 L_result += STEP(2) ; L_result += STEP(3) ;
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90 L_result += STEP(4) ; L_result += STEP(5) ;
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91 L_result += STEP(6) ; L_result += STEP(7) ;
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92 L_result += STEP(8) ; L_result += STEP(9) ;
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93 L_result += STEP(10) ; L_result += STEP(11) ;
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94 L_result += STEP(12) ; L_result += STEP(13) ;
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95 L_result += STEP(14) ; L_result += STEP(15) ;
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96 L_result += STEP(16) ; L_result += STEP(17) ;
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97 L_result += STEP(18) ; L_result += STEP(19) ;
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98 L_result += STEP(20) ; L_result += STEP(21) ;
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99 L_result += STEP(22) ; L_result += STEP(23) ;
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100 L_result += STEP(24) ; L_result += STEP(25) ;
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101 L_result += STEP(26) ; L_result += STEP(27) ;
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102 L_result += STEP(28) ; L_result += STEP(29) ;
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103 L_result += STEP(30) ; L_result += STEP(31) ;
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104 L_result += STEP(32) ; L_result += STEP(33) ;
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105 L_result += STEP(34) ; L_result += STEP(35) ;
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106 L_result += STEP(36) ; L_result += STEP(37) ;
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107 L_result += STEP(38) ; L_result += STEP(39) ;
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108
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109 if (L_result > L_max) {
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110
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111 Nc = lambda;
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112 L_max = L_result;
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113 }
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114 }
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115
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116 *Nc_out = Nc;
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117
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118 L_max <<= 1;
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119
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120 /* Rescaling of L_max
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121 */
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122 assert(scal <= 100 && scal >= -100);
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123 L_max = L_max >> (6 - scal); /* sub(6, scal) */
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124
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125 assert( Nc <= 120 && Nc >= 40);
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diff changeset
126
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diff changeset
127 /* Compute the power of the reconstructed short term residual
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parents:
diff changeset
128 * signal dp[..]
65d3304502bd libgsmfr2: integrate long_term.c from libgsm
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diff changeset
129 */
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130 L_power = 0;
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parents:
diff changeset
131 for (k = 0; k <= 39; k++) {
65d3304502bd libgsmfr2: integrate long_term.c from libgsm
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parents:
diff changeset
132
65d3304502bd libgsmfr2: integrate long_term.c from libgsm
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diff changeset
133 register longword L_temp;
65d3304502bd libgsmfr2: integrate long_term.c from libgsm
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diff changeset
134
65d3304502bd libgsmfr2: integrate long_term.c from libgsm
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diff changeset
135 L_temp = SASR( dp[k - Nc], 3 );
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parents:
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136 L_power += L_temp * L_temp;
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diff changeset
137 }
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parents:
diff changeset
138 L_power <<= 1; /* from L_MULT */
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diff changeset
139
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parents:
diff changeset
140 /* Normalization of L_max and L_power
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parents:
diff changeset
141 */
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diff changeset
142
65d3304502bd libgsmfr2: integrate long_term.c from libgsm
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
143 if (L_max <= 0) {
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diff changeset
144 *bc_out = 0;
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Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
145 return;
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Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
146 }
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diff changeset
147 if (L_max >= L_power) {
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148 *bc_out = 3;
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parents:
diff changeset
149 return;
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150 }
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151
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Mychaela Falconia <falcon@freecalypso.org>
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152 temp = gsm_norm( L_power );
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153
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154 R = SASR( L_max << temp, 16 );
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parents:
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155 S = SASR( L_power << temp, 16 );
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parents:
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156
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Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
157 /* Coding of the LTP gain
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158 */
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parents:
diff changeset
159
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parents:
diff changeset
160 /* Table 4.3a must be used to obtain the level DLB[i] for the
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parents:
diff changeset
161 * quantization of the LTP gain b to get the coded version bc.
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162 */
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Mychaela Falconia <falcon@freecalypso.org>
parents:
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163 for (bc = 0; bc <= 2; bc++) if (R <= gsm_mult(S, gsm_DLB[bc])) break;
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Mychaela Falconia <falcon@freecalypso.org>
parents:
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164 *bc_out = bc;
65d3304502bd libgsmfr2: integrate long_term.c from libgsm
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parents:
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165 }
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166
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diff changeset
167 /* 4.2.12 */
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diff changeset
168
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diff changeset
169 static void Long_term_analysis_filtering (
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170 word bc, /* IN */
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diff changeset
171 word Nc, /* IN */
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parents:
diff changeset
172 register word * dp, /* previous d [-120..-1] IN */
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parents:
diff changeset
173 register word * d, /* d [0..39] IN */
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parents:
diff changeset
174 register word * dpp, /* estimate [0..39] OUT */
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parents:
diff changeset
175 register word * e /* long term res. signal [0..39] OUT */
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parents:
diff changeset
176 )
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177 /*
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178 * In this part, we have to decode the bc parameter to compute
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parents:
diff changeset
179 * the samples of the estimate dpp[0..39]. The decoding of bc needs the
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parents:
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180 * use of table 4.3b. The long term residual signal e[0..39]
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parents:
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181 * is then calculated to be fed to the RPE encoding section.
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182 */
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183 {
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184 register int k;
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parents:
diff changeset
185 register longword ltmp;
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186
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187 # undef STEP
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188 # define STEP(BP) \
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189 for (k = 0; k <= 39; k++) { \
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parents:
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190 dpp[k] = GSM_MULT_R( BP, dp[k - Nc]); \
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parents:
diff changeset
191 e[k] = GSM_SUB( d[k], dpp[k] ); \
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192 }
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193
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194 switch (bc) {
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parents:
diff changeset
195 case 0: STEP( 3277 ); break;
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parents:
diff changeset
196 case 1: STEP( 11469 ); break;
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parents:
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197 case 2: STEP( 21299 ); break;
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198 case 3: STEP( 32767 ); break;
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diff changeset
199 }
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diff changeset
200 }
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diff changeset
201
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Mychaela Falconia <falcon@freecalypso.org>
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diff changeset
202 void Gsm_Long_Term_Predictor ( /* 4x for 160 samples */
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parents:
diff changeset
203 struct gsmfr_0610_state * S,
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parents:
diff changeset
204
65d3304502bd libgsmfr2: integrate long_term.c from libgsm
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diff changeset
205 word * d, /* [0..39] residual signal IN */
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parents:
diff changeset
206 word * dp, /* [-120..-1] d' IN */
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parents:
diff changeset
207
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diff changeset
208 word * e, /* [0..39] OUT */
65d3304502bd libgsmfr2: integrate long_term.c from libgsm
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parents:
diff changeset
209 word * dpp, /* [0..39] OUT */
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parents:
diff changeset
210 word * Nc, /* correlation lag OUT */
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parents:
diff changeset
211 word * bc /* gain factor OUT */
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parents:
diff changeset
212 )
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Mychaela Falconia <falcon@freecalypso.org>
parents:
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213 {
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parents:
diff changeset
214 assert( d ); assert( dp ); assert( e );
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parents:
diff changeset
215 assert( dpp); assert( Nc ); assert( bc );
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parents:
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216
65d3304502bd libgsmfr2: integrate long_term.c from libgsm
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diff changeset
217 Calculation_of_the_LTP_parameters(d, dp, bc, Nc);
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parents:
diff changeset
218 Long_term_analysis_filtering( *bc, *Nc, dp, d, dpp, e );
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parents:
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219 }
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220
65d3304502bd libgsmfr2: integrate long_term.c from libgsm
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diff changeset
221 /* 4.3.2 */
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parents:
diff changeset
222 void Gsm_Long_Term_Synthesis_Filtering (
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parents:
diff changeset
223 struct gsmfr_0610_state * S,
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parents:
diff changeset
224
65d3304502bd libgsmfr2: integrate long_term.c from libgsm
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diff changeset
225 word Ncr,
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diff changeset
226 word bcr,
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Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
227 register word * erp, /* [0..39] IN */
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parents:
diff changeset
228 register word * drp /* [-120..-1] IN, [-120..40] OUT */
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parents:
diff changeset
229 )
65d3304502bd libgsmfr2: integrate long_term.c from libgsm
Mychaela Falconia <falcon@freecalypso.org>
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diff changeset
230 /*
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parents:
diff changeset
231 * This procedure uses the bcr and Ncr parameter to realize the
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parents:
diff changeset
232 * long term synthesis filtering. The decoding of bcr needs
65d3304502bd libgsmfr2: integrate long_term.c from libgsm
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
233 * table 4.3b.
65d3304502bd libgsmfr2: integrate long_term.c from libgsm
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
234 */
65d3304502bd libgsmfr2: integrate long_term.c from libgsm
Mychaela Falconia <falcon@freecalypso.org>
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diff changeset
235 {
65d3304502bd libgsmfr2: integrate long_term.c from libgsm
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
236 register longword ltmp; /* for ADD */
65d3304502bd libgsmfr2: integrate long_term.c from libgsm
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
237 register int k;
65d3304502bd libgsmfr2: integrate long_term.c from libgsm
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
238 word brp, drpp, Nr;
65d3304502bd libgsmfr2: integrate long_term.c from libgsm
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
239
65d3304502bd libgsmfr2: integrate long_term.c from libgsm
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
240 /* Check the limits of Nr.
65d3304502bd libgsmfr2: integrate long_term.c from libgsm
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
241 */
65d3304502bd libgsmfr2: integrate long_term.c from libgsm
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
242 Nr = Ncr < 40 || Ncr > 120 ? S->nrp : Ncr;
65d3304502bd libgsmfr2: integrate long_term.c from libgsm
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
243 S->nrp = Nr;
65d3304502bd libgsmfr2: integrate long_term.c from libgsm
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
244 assert(Nr >= 40 && Nr <= 120);
65d3304502bd libgsmfr2: integrate long_term.c from libgsm
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parents:
diff changeset
245
65d3304502bd libgsmfr2: integrate long_term.c from libgsm
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
246 /* Decoding of the LTP gain bcr
65d3304502bd libgsmfr2: integrate long_term.c from libgsm
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
247 */
65d3304502bd libgsmfr2: integrate long_term.c from libgsm
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
248 brp = gsm_QLB[ bcr ];
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diff changeset
249
65d3304502bd libgsmfr2: integrate long_term.c from libgsm
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
250 /* Computation of the reconstructed short term residual
65d3304502bd libgsmfr2: integrate long_term.c from libgsm
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
251 * signal drp[0..39]
65d3304502bd libgsmfr2: integrate long_term.c from libgsm
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
252 */
65d3304502bd libgsmfr2: integrate long_term.c from libgsm
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
253 assert(brp != MIN_WORD);
65d3304502bd libgsmfr2: integrate long_term.c from libgsm
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parents:
diff changeset
254
65d3304502bd libgsmfr2: integrate long_term.c from libgsm
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
255 for (k = 0; k <= 39; k++) {
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256 drpp = GSM_MULT_R( brp, drp[ k - Nr ] );
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257 drp[k] = GSM_ADD( erp[k], drpp );
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258 }
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259
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260 /*
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261 * Update of the reconstructed short term residual signal
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262 * drp[ -1..-120 ]
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263 */
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264
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265 for (k = 0; k <= 119; k++) drp[ -120 + k ] = drp[ -80 + k ];
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266 }