1 | /* j0.c |
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2 | * |
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3 | * Bessel function of order zero |
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4 | * |
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5 | * |
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6 | * |
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7 | * SYNOPSIS: |
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8 | * |
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9 | * double x, y, j0(); |
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10 | * |
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11 | * y = j0( x ); |
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12 | * |
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13 | * |
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14 | * |
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15 | * DESCRIPTION: |
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16 | * |
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17 | * Returns Bessel function of order zero of the argument. |
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18 | * |
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19 | * The domain is divided into the intervals [0, 5] and |
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20 | * (5, infinity). In the first interval the following rational |
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21 | * approximation is used: |
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22 | * |
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23 | * |
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24 | * 2 2 |
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25 | * (w - r ) (w - r ) P (w) / Q (w) |
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26 | * 1 2 3 8 |
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27 | * |
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28 | * 2 |
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29 | * where w = x and the two r's are zeros of the function. |
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30 | * |
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31 | * In the second interval, the Hankel asymptotic expansion |
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32 | * is employed with two rational functions of degree 6/6 |
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33 | * and 7/7. |
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34 | * |
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35 | * |
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36 | * |
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37 | * ACCURACY: |
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38 | * |
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39 | * Absolute error: |
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40 | * arithmetic domain # trials peak rms |
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41 | * DEC 0, 30 10000 4.4e-17 6.3e-18 |
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42 | * IEEE 0, 30 60000 4.2e-16 1.1e-16 |
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43 | * |
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44 | */ |
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45 | |
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46 | /* |
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47 | Cephes Math Library Release 2.8: June, 2000 |
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48 | Copyright 1984, 1987, 1989, 2000 by Stephen L. Moshier |
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49 | */ |
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50 | |
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51 | /* Note: all coefficients satisfy the relative error criterion |
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52 | * except YP, YQ which are designed for absolute error. */ |
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53 | |
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54 | #if FLOAT_SIZE>4 |
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55 | //Cephes double precission |
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56 | double cephes_j0(double x); |
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57 | |
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58 | constant double PPJ0[8] = { |
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59 | 7.96936729297347051624E-4, |
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60 | 8.28352392107440799803E-2, |
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61 | 1.23953371646414299388E0, |
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62 | 5.44725003058768775090E0, |
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63 | 8.74716500199817011941E0, |
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64 | 5.30324038235394892183E0, |
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65 | 9.99999999999999997821E-1, |
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66 | 0.0 |
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67 | }; |
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68 | |
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69 | constant double PQJ0[8] = { |
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70 | 9.24408810558863637013E-4, |
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71 | 8.56288474354474431428E-2, |
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72 | 1.25352743901058953537E0, |
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73 | 5.47097740330417105182E0, |
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74 | 8.76190883237069594232E0, |
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75 | 5.30605288235394617618E0, |
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76 | 1.00000000000000000218E0, |
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77 | 0.0 |
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78 | }; |
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79 | |
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80 | constant double QPJ0[8] = { |
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81 | -1.13663838898469149931E-2, |
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82 | -1.28252718670509318512E0, |
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83 | -1.95539544257735972385E1, |
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84 | -9.32060152123768231369E1, |
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85 | -1.77681167980488050595E2, |
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86 | -1.47077505154951170175E2, |
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87 | -5.14105326766599330220E1, |
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88 | -6.05014350600728481186E0, |
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89 | }; |
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90 | |
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91 | constant double QQJ0[8] = { |
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92 | /* 1.00000000000000000000E0,*/ |
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93 | 6.43178256118178023184E1, |
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94 | 8.56430025976980587198E2, |
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95 | 3.88240183605401609683E3, |
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96 | 7.24046774195652478189E3, |
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97 | 5.93072701187316984827E3, |
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98 | 2.06209331660327847417E3, |
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99 | 2.42005740240291393179E2, |
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100 | }; |
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101 | |
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102 | constant double YPJ0[8] = { |
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103 | 1.55924367855235737965E4, |
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104 | -1.46639295903971606143E7, |
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105 | 5.43526477051876500413E9, |
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106 | -9.82136065717911466409E11, |
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107 | 8.75906394395366999549E13, |
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108 | -3.46628303384729719441E15, |
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109 | 4.42733268572569800351E16, |
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110 | -1.84950800436986690637E16, |
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111 | }; |
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112 | |
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113 | |
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114 | constant double YQJ0[7] = { |
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115 | /* 1.00000000000000000000E0,*/ |
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116 | 1.04128353664259848412E3, |
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117 | 6.26107330137134956842E5, |
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118 | 2.68919633393814121987E8, |
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119 | 8.64002487103935000337E10, |
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120 | 2.02979612750105546709E13, |
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121 | 3.17157752842975028269E15, |
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122 | 2.50596256172653059228E17, |
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123 | }; |
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124 | |
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125 | constant double RPJ0[8] = { |
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126 | -4.79443220978201773821E9, |
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127 | 1.95617491946556577543E12, |
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128 | -2.49248344360967716204E14, |
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129 | 9.70862251047306323952E15, |
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130 | 0.0, |
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131 | 0.0, |
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132 | 0.0, |
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133 | 0.0 |
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134 | }; |
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135 | |
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136 | constant double RQJ0[8] = { |
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137 | /* 1.00000000000000000000E0,*/ |
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138 | 4.99563147152651017219E2, |
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139 | 1.73785401676374683123E5, |
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140 | 4.84409658339962045305E7, |
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141 | 1.11855537045356834862E10, |
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142 | 2.11277520115489217587E12, |
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143 | 3.10518229857422583814E14, |
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144 | 3.18121955943204943306E16, |
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145 | 1.71086294081043136091E18, |
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146 | }; |
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147 | |
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148 | double cephes_j0(double x) |
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149 | { |
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150 | double w, z, p, q, xn; |
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151 | |
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152 | //const double TWOOPI = 6.36619772367581343075535E-1; |
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153 | const double SQ2OPI = 7.9788456080286535587989E-1; |
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154 | const double PIO4 = 7.85398163397448309616E-1; |
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155 | |
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156 | const double DR1 = 5.78318596294678452118E0; |
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157 | const double DR2 = 3.04712623436620863991E1; |
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158 | |
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159 | |
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160 | if( x < 0 ) |
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161 | x = -x; |
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162 | |
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163 | if( x <= 5.0 ) { |
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164 | z = x * x; |
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165 | if( x < 1.0e-5 ) |
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166 | return( 1.0 - z/4.0 ); |
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167 | |
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168 | p = (z - DR1) * (z - DR2); |
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169 | p = p * polevl( z, RPJ0, 3)/p1evl( z, RQJ0, 8 ); |
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170 | return( p ); |
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171 | } |
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172 | |
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173 | w = 5.0/x; |
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174 | q = 25.0/(x*x); |
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175 | p = polevl( q, PPJ0, 6)/polevl( q, PQJ0, 6 ); |
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176 | q = polevl( q, QPJ0, 7)/p1evl( q, QQJ0, 7 ); |
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177 | xn = x - PIO4; |
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178 | |
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179 | double sn, cn; |
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180 | SINCOS(xn, sn, cn); |
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181 | p = p * cn - w * q * sn; |
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182 | |
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183 | return( p * SQ2OPI / sqrt(x) ); |
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184 | } |
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185 | #else |
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186 | //Cephes single precission |
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187 | float cephes_j0f(float x); |
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188 | |
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189 | constant float MOJ0[8] = { |
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190 | -6.838999669318810E-002, |
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191 | 1.864949361379502E-001, |
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192 | -2.145007480346739E-001, |
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193 | 1.197549369473540E-001, |
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194 | -3.560281861530129E-003, |
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195 | -4.969382655296620E-002, |
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196 | -3.355424622293709E-006, |
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197 | 7.978845717621440E-001 |
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198 | }; |
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199 | |
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200 | constant float PHJ0[8] = { |
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201 | 3.242077816988247E+001, |
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202 | -3.630592630518434E+001, |
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203 | 1.756221482109099E+001, |
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204 | -4.974978466280903E+000, |
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205 | 1.001973420681837E+000, |
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206 | -1.939906941791308E-001, |
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207 | 6.490598792654666E-002, |
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208 | -1.249992184872738E-001 |
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209 | }; |
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210 | |
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211 | constant float JPJ0[8] = { |
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212 | -6.068350350393235E-008, |
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213 | 6.388945720783375E-006, |
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214 | -3.969646342510940E-004, |
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215 | 1.332913422519003E-002, |
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216 | -1.729150680240724E-001, |
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217 | 0.0, |
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218 | 0.0, |
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219 | 0.0 |
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220 | }; |
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221 | |
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222 | float cephes_j0f(float x) |
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223 | { |
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224 | float xx, w, z, p, q, xn; |
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225 | |
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226 | //const double YZ1 = 0.43221455686510834878; |
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227 | //const double YZ2 = 22.401876406482861405; |
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228 | //const double YZ3 = 64.130620282338755553; |
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229 | const float DR1 = 5.78318596294678452118; |
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230 | const float PIO4F = 0.7853981633974483096; |
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231 | |
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232 | if( x < 0 ) |
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233 | xx = -x; |
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234 | else |
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235 | xx = x; |
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236 | |
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237 | // 2017-05-18 PAK - support negative x |
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238 | if( xx <= 2.0 ) { |
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239 | z = xx * xx; |
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240 | if( xx < 1.0e-3 ) |
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241 | return( 1.0 - 0.25*z ); |
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242 | |
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243 | p = (z-DR1) * polevl( z, JPJ0, 4); |
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244 | return( p ); |
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245 | } |
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246 | |
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247 | q = 1.0/xx; |
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248 | w = sqrt(q); |
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249 | |
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250 | p = w * polevl( q, MOJ0, 7); |
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251 | w = q*q; |
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252 | xn = q * polevl( w, PHJ0, 7) - PIO4F; |
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253 | p = p * cos(xn + xx); |
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254 | return(p); |
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255 | } |
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256 | #endif |
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257 | |
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258 | #if FLOAT_SIZE>4 |
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259 | #define sas_J0 cephes_j0 |
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260 | #else |
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261 | #define sas_J0 cephes_j0f |
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262 | #endif |
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