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annotate libgsmefr/levinson.c @ 122:b33f2168fdec

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doc/EFR-rationale article written
author Mychaela Falconia <falcon@freecalypso.org>
date Sat, 10 Dec 2022 08:51:01 +0000
parents 0e41ca9ebf45
children 1cdbaeec7bcc
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1 /*************************************************************************
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2 *
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3 * FUNCTION: Levinson()
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4 *
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5 * PURPOSE: Levinson-Durbin algorithm in double precision. To compute the
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6 * LP filter parameters from the speech autocorrelations.
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7 *
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8 * DESCRIPTION:
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9 * R[i] autocorrelations.
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10 * A[i] filter coefficients.
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11 * K reflection coefficients.
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12 * Alpha prediction gain.
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13 *
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14 * Initialisation:
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15 * A[0] = 1
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16 * K = -R[1]/R[0]
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17 * A[1] = K
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18 * Alpha = R[0] * (1-K**2]
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19 *
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20 * Do for i = 2 to M
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21 *
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22 * S = SUM ( R[j]*A[i-j] ,j=1,i-1 ) + R[i]
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23 *
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24 * K = -S / Alpha
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25 *
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26 * An[j] = A[j] + K*A[i-j] for j=1 to i-1
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27 * where An[i] = new A[i]
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28 * An[i]=K
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29 *
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30 * Alpha=Alpha * (1-K**2)
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31 *
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32 * END
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33 *
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34 *************************************************************************/
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35
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36 #include "gsm_efr.h"
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37 #include "typedef.h"
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38 #include "namespace.h"
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39 #include "basic_op.h"
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40 #include "oper_32b.h"
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41 #include "no_count.h"
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42 #include "sig_proc.h"
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43 #include "cnst.h"
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44 #include "enc_state.h"
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45
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46 /* Lpc order == 10 */
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47
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48 #define M 10
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49
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50 void Levinson (
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51 struct EFR_encoder_state *st,
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52 Word16 Rh[], /* (i) : Rh[m+1] Vector of autocorrelations (msb) */
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53 Word16 Rl[], /* (i) : Rl[m+1] Vector of autocorrelations (lsb) */
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54 Word16 A[], /* (o) : A[m] LPC coefficients (m = 10) */
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55 Word16 rc[] /* (o) : rc[4] First 4 reflection coefficients */
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56
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57 )
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58 {
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59 Word16 i, j;
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60 Word16 hi, lo;
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61 Word16 Kh, Kl; /* reflexion coefficient; hi and lo */
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62 Word16 alp_h, alp_l, alp_exp; /* Prediction gain; hi lo and exponent */
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63 Word16 Ah[M + 1], Al[M + 1]; /* LPC coef. in double prec. */
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64 Word16 Anh[M + 1], Anl[M + 1];/* LPC coef.for next iteration in double
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65 prec. */
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66 Word32 t0, t1, t2; /* temporary variable */
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67
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68 /* K = A[1] = -R[1] / R[0] */
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69
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70 t1 = L_Comp (Rh[1], Rl[1]);
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71 t2 = L_abs (t1); /* abs R[1] */
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72 t0 = Div_32 (t2, Rh[0], Rl[0]); /* R[1]/R[0] */
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73 test ();
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74 if (t1 > 0)
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75 t0 = L_negate (t0); /* -R[1]/R[0] */
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76 L_Extract (t0, &Kh, &Kl); /* K in DPF */
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77
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78 rc[0] = round (t0); move16 ();
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79
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80 t0 = L_shr (t0, 4); /* A[1] in */
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81 L_Extract (t0, &Ah[1], &Al[1]); /* A[1] in DPF */
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82
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83 /* Alpha = R[0] * (1-K**2) */
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84
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85 t0 = Mpy_32 (Kh, Kl, Kh, Kl); /* K*K */
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86 t0 = L_abs (t0); /* Some case <0 !! */
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87 t0 = L_sub ((Word32) 0x7fffffffL, t0); /* 1 - K*K */
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88 L_Extract (t0, &hi, &lo); /* DPF format */
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89 t0 = Mpy_32 (Rh[0], Rl[0], hi, lo); /* Alpha in */
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90
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91 /* Normalize Alpha */
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92
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93 alp_exp = norm_l (t0);
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94 t0 = L_shl (t0, alp_exp);
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95 L_Extract (t0, &alp_h, &alp_l); /* DPF format */
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96
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97 /*--------------------------------------*
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98 * ITERATIONS I=2 to M *
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99 *--------------------------------------*/
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100
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101 for (i = 2; i <= M; i++)
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102 {
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103 /* t0 = SUM ( R[j]*A[i-j] ,j=1,i-1 ) + R[i] */
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104
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105 t0 = 0; move32 ();
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106 for (j = 1; j < i; j++)
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107 {
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108 t0 = L_add (t0, Mpy_32 (Rh[j], Rl[j], Ah[i - j], Al[i - j]));
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109 }
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110 t0 = L_shl (t0, 4);
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111
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112 t1 = L_Comp (Rh[i], Rl[i]);
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113 t0 = L_add (t0, t1); /* add R[i] */
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114
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115 /* K = -t0 / Alpha */
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116
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117 t1 = L_abs (t0);
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118 t2 = Div_32 (t1, alp_h, alp_l); /* abs(t0)/Alpha */
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119 test ();
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120 if (t0 > 0)
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121 t2 = L_negate (t2); /* K =-t0/Alpha */
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122 t2 = L_shl (t2, alp_exp); /* denormalize; compare to Alpha */
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123 L_Extract (t2, &Kh, &Kl); /* K in DPF */
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124
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125 test ();
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126 if (sub (i, 5) < 0)
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127 {
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128 rc[i - 1] = round (t2); move16 ();
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129 }
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130 /* Test for unstable filter. If unstable keep old A(z) */
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131
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132 if (sub (abs_s (Kh), 32750) > 0)
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133 {
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134 for (j = 0; j <= M; j++)
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135 {
76
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136 A[j] = st->old_A[j];
53
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137 }
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138
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139 for (j = 0; j < 4; j++)
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140 {
76
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141 rc[j] = 0;
53
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142 }
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143
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144 return;
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145 }
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146 /*------------------------------------------*
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147 * Compute new LPC coeff. -> An[i] *
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148 * An[j]= A[j] + K*A[i-j] , j=1 to i-1 *
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149 * An[i]= K *
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150 *------------------------------------------*/
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151
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152 for (j = 1; j < i; j++)
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153 {
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154 t0 = Mpy_32 (Kh, Kl, Ah[i - j], Al[i - j]);
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155 t0 = L_mac (t0, Ah[j], 32767);
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156 t0 = L_mac (t0, Al[j], 1);
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157 L_Extract (t0, &Anh[j], &Anl[j]);
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158 }
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159 t2 = L_shr (t2, 4);
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160 L_Extract (t2, &Anh[i], &Anl[i]);
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161
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162 /* Alpha = Alpha * (1-K**2) */
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163
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164 t0 = Mpy_32 (Kh, Kl, Kh, Kl); /* K*K */
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165 t0 = L_abs (t0); /* Some case <0 !! */
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166 t0 = L_sub ((Word32) 0x7fffffffL, t0); /* 1 - K*K */
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167 L_Extract (t0, &hi, &lo); /* DPF format */
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168 t0 = Mpy_32 (alp_h, alp_l, hi, lo);
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diff changeset
169
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170 /* Normalize Alpha */
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171
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172 j = norm_l (t0);
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173 t0 = L_shl (t0, j);
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174 L_Extract (t0, &alp_h, &alp_l); /* DPF format */
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175 alp_exp = add (alp_exp, j); /* Add normalization to
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176 alp_exp */
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diff changeset
177
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178 /* A[j] = An[j] */
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diff changeset
179
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180 for (j = 1; j <= i; j++)
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diff changeset
181 {
49dd1ac8e75b libgsmefr: import most *.c files from ETSI source
Mychaela Falconia <falcon@freecalypso.org>
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182 Ah[j] = Anh[j]; move16 ();
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parents:
diff changeset
183 Al[j] = Anl[j]; move16 ();
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parents:
diff changeset
184 }
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Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
185 }
49dd1ac8e75b libgsmefr: import most *.c files from ETSI source
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
186
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187 A[0] = 4096; move16 ();
49dd1ac8e75b libgsmefr: import most *.c files from ETSI source
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parents:
diff changeset
188 for (i = 1; i <= M; i++)
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Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
189 {
49dd1ac8e75b libgsmefr: import most *.c files from ETSI source
Mychaela Falconia <falcon@freecalypso.org>
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190 t0 = L_Comp (Ah[i], Al[i]);
76
0e41ca9ebf45 libgsmefr: levinson.c compiles
Mychaela Falconia <falcon@freecalypso.org>
parents: 53
diff changeset
191 st->old_A[i] = A[i] = round (L_shl (t0, 1));
53
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Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
192 }
49dd1ac8e75b libgsmefr: import most *.c files from ETSI source
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
193
49dd1ac8e75b libgsmefr: import most *.c files from ETSI source
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
194 return;
49dd1ac8e75b libgsmefr: import most *.c files from ETSI source
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
195 }