FreeCalypso > hg > gsm-codec-lib
annotate libgsmefr/levinson.c @ 66:824ff833bda9
libgsmefr/dtx.c: initial import from ETSI code
author | Mychaela Falconia <falcon@freecalypso.org> |
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date | Sat, 26 Nov 2022 03:52:39 +0000 |
parents | 49dd1ac8e75b |
children | 0e41ca9ebf45 |
rev | line source |
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libgsmefr: import most *.c files from ETSI source
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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 "typedef.h" |
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37 #include "basic_op.h" |
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38 #include "oper_32b.h" |
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39 #include "count.h" |
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40 |
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41 /* Lpc order == 10 */ |
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42 |
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43 #define M 10 |
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44 |
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45 /* Last A(z) for case of unstable filter */ |
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46 |
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47 Word16 old_A[M + 1]; |
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48 |
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49 void Levinson ( |
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50 Word16 Rh[], /* (i) : Rh[m+1] Vector of autocorrelations (msb) */ |
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51 Word16 Rl[], /* (i) : Rl[m+1] Vector of autocorrelations (lsb) */ |
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52 Word16 A[], /* (o) : A[m] LPC coefficients (m = 10) */ |
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53 Word16 rc[] /* (o) : rc[4] First 4 reflection coefficients */ |
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54 |
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55 ) |
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56 { |
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57 Word16 i, j; |
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58 Word16 hi, lo; |
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59 Word16 Kh, Kl; /* reflexion coefficient; hi and lo */ |
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60 Word16 alp_h, alp_l, alp_exp; /* Prediction gain; hi lo and exponent */ |
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61 Word16 Ah[M + 1], Al[M + 1]; /* LPC coef. in double prec. */ |
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62 Word16 Anh[M + 1], Anl[M + 1];/* LPC coef.for next iteration in double |
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63 prec. */ |
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64 Word32 t0, t1, t2; /* temporary variable */ |
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65 |
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66 /* K = A[1] = -R[1] / R[0] */ |
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67 |
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68 t1 = L_Comp (Rh[1], Rl[1]); |
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69 t2 = L_abs (t1); /* abs R[1] */ |
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70 t0 = Div_32 (t2, Rh[0], Rl[0]); /* R[1]/R[0] */ |
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71 test (); |
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72 if (t1 > 0) |
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73 t0 = L_negate (t0); /* -R[1]/R[0] */ |
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74 L_Extract (t0, &Kh, &Kl); /* K in DPF */ |
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75 |
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76 rc[0] = round (t0); move16 (); |
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77 |
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78 t0 = L_shr (t0, 4); /* A[1] in */ |
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79 L_Extract (t0, &Ah[1], &Al[1]); /* A[1] in DPF */ |
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80 |
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81 /* Alpha = R[0] * (1-K**2) */ |
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82 |
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83 t0 = Mpy_32 (Kh, Kl, Kh, Kl); /* K*K */ |
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84 t0 = L_abs (t0); /* Some case <0 !! */ |
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85 t0 = L_sub ((Word32) 0x7fffffffL, t0); /* 1 - K*K */ |
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86 L_Extract (t0, &hi, &lo); /* DPF format */ |
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87 t0 = Mpy_32 (Rh[0], Rl[0], hi, lo); /* Alpha in */ |
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88 |
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89 /* Normalize Alpha */ |
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90 |
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91 alp_exp = norm_l (t0); |
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92 t0 = L_shl (t0, alp_exp); |
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93 L_Extract (t0, &alp_h, &alp_l); /* DPF format */ |
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94 |
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95 /*--------------------------------------* |
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96 * ITERATIONS I=2 to M * |
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97 *--------------------------------------*/ |
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98 |
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99 for (i = 2; i <= M; i++) |
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100 { |
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101 /* t0 = SUM ( R[j]*A[i-j] ,j=1,i-1 ) + R[i] */ |
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102 |
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103 t0 = 0; move32 (); |
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104 for (j = 1; j < i; j++) |
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105 { |
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106 t0 = L_add (t0, Mpy_32 (Rh[j], Rl[j], Ah[i - j], Al[i - j])); |
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107 } |
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108 t0 = L_shl (t0, 4); |
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109 |
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110 t1 = L_Comp (Rh[i], Rl[i]); |
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111 t0 = L_add (t0, t1); /* add R[i] */ |
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112 |
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113 /* K = -t0 / Alpha */ |
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114 |
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115 t1 = L_abs (t0); |
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116 t2 = Div_32 (t1, alp_h, alp_l); /* abs(t0)/Alpha */ |
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117 test (); |
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118 if (t0 > 0) |
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119 t2 = L_negate (t2); /* K =-t0/Alpha */ |
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120 t2 = L_shl (t2, alp_exp); /* denormalize; compare to Alpha */ |
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121 L_Extract (t2, &Kh, &Kl); /* K in DPF */ |
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122 |
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123 test (); |
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124 if (sub (i, 5) < 0) |
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125 { |
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126 rc[i - 1] = round (t2); move16 (); |
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127 } |
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128 /* Test for unstable filter. If unstable keep old A(z) */ |
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129 |
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130 test (); |
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131 if (sub (abs_s (Kh), 32750) > 0) |
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132 { |
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133 for (j = 0; j <= M; j++) |
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134 { |
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135 A[j] = old_A[j]; move16 (); |
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136 } |
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137 |
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138 for (j = 0; j < 4; j++) |
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139 { |
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140 rc[j] = 0; move16 (); |
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141 } |
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142 |
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143 return; |
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144 } |
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145 /*------------------------------------------* |
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146 * Compute new LPC coeff. -> An[i] * |
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147 * An[j]= A[j] + K*A[i-j] , j=1 to i-1 * |
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148 * An[i]= K * |
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149 *------------------------------------------*/ |
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150 |
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151 for (j = 1; j < i; j++) |
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152 { |
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153 t0 = Mpy_32 (Kh, Kl, Ah[i - j], Al[i - j]); |
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154 t0 = L_mac (t0, Ah[j], 32767); |
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155 t0 = L_mac (t0, Al[j], 1); |
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156 L_Extract (t0, &Anh[j], &Anl[j]); |
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157 } |
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158 t2 = L_shr (t2, 4); |
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159 L_Extract (t2, &Anh[i], &Anl[i]); |
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160 |
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161 /* Alpha = Alpha * (1-K**2) */ |
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162 |
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163 t0 = Mpy_32 (Kh, Kl, Kh, Kl); /* K*K */ |
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164 t0 = L_abs (t0); /* Some case <0 !! */ |
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165 t0 = L_sub ((Word32) 0x7fffffffL, t0); /* 1 - K*K */ |
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166 L_Extract (t0, &hi, &lo); /* DPF format */ |
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167 t0 = Mpy_32 (alp_h, alp_l, hi, lo); |
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168 |
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169 /* Normalize Alpha */ |
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170 |
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171 j = norm_l (t0); |
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172 t0 = L_shl (t0, j); |
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173 L_Extract (t0, &alp_h, &alp_l); /* DPF format */ |
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174 alp_exp = add (alp_exp, j); /* Add normalization to |
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175 alp_exp */ |
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176 |
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177 /* A[j] = An[j] */ |
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178 |
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179 for (j = 1; j <= i; j++) |
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180 { |
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181 Ah[j] = Anh[j]; move16 (); |
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182 Al[j] = Anl[j]; move16 (); |
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183 } |
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184 } |
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185 |
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186 A[0] = 4096; move16 (); |
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187 for (i = 1; i <= M; i++) |
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188 { |
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189 t0 = L_Comp (Ah[i], Al[i]); |
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190 old_A[i] = A[i] = round (L_shl (t0, 1));move16 (); move16 (); |
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191 } |
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192 |
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193 return; |
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194 } |