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annotate libgsmefr/levinson.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 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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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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parents: 53
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136 A[j] = st->old_A[j];
53
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137 }
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parents:
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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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Mychaela Falconia <falcon@freecalypso.org>
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diff changeset
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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Mychaela Falconia <falcon@freecalypso.org>
parents:
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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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Mychaela Falconia <falcon@freecalypso.org>
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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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parents:
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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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parents:
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166 t0 = L_sub ((Word32) 0x7fffffffL, t0); /* 1 - K*K */
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parents:
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167 L_Extract (t0, &hi, &lo); /* DPF format */
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parents:
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168 t0 = Mpy_32 (alp_h, alp_l, hi, lo);
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parents:
diff changeset
169
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170 /* Normalize Alpha */
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diff changeset
171
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172 j = norm_l (t0);
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parents:
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173 t0 = L_shl (t0, j);
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parents:
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174 L_Extract (t0, &alp_h, &alp_l); /* DPF format */
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parents:
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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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parents:
diff changeset
179
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parents:
diff changeset
180 for (j = 1; j <= i; j++)
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Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
181 {
49dd1ac8e75b libgsmefr: import most *.c files from ETSI source
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
182 Ah[j] = Anh[j]; move16 ();
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Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
183 Al[j] = Anl[j]; move16 ();
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Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
184 }
49dd1ac8e75b libgsmefr: import most *.c files from ETSI source
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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Mychaela Falconia <falcon@freecalypso.org>
parents:
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187 A[0] = 4096; move16 ();
49dd1ac8e75b libgsmefr: import most *.c files from ETSI source
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
188 for (i = 1; i <= M; i++)
49dd1ac8e75b libgsmefr: import most *.c files from ETSI source
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
189 {
49dd1ac8e75b libgsmefr: import most *.c files from ETSI source
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
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 }