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1 /* Compute complex base 10 logarithm.
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2 Copyright (C) 1997-2018 Free Software Foundation, Inc.
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3 This file is part of the GNU C Library.
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4 Contributed by Ulrich Drepper <drepper@cygnus.com>, 1997.
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5
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6 The GNU C Library is free software; you can redistribute it and/or
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7 modify it under the terms of the GNU Lesser General Public
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8 License as published by the Free Software Foundation; either
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9 version 2.1 of the License, or (at your option) any later version.
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10
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11 The GNU C Library is distributed in the hope that it will be useful,
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12 but WITHOUT ANY WARRANTY; without even the implied warranty of
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13 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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14 Lesser General Public License for more details.
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15
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16 You should have received a copy of the GNU Lesser General Public
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17 License along with the GNU C Library; if not, see
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18 <http://www.gnu.org/licenses/>. */
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19
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20 #include "quadmath-imp.h"
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21
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22 /* log_10 (2). */
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23 #define LOG10_2 0.3010299956639811952137388947244930267682Q
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24
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25 /* pi * log10 (e). */
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26 #define PI_LOG10E 1.364376353841841347485783625431355770210Q
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27
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28 __complex128
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29 clog10q (__complex128 x)
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30 {
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31 __complex128 result;
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32 int rcls = fpclassifyq (__real__ x);
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33 int icls = fpclassifyq (__imag__ x);
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34
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35 if (__glibc_unlikely (rcls == QUADFP_ZERO && icls == QUADFP_ZERO))
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36 {
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37 /* Real and imaginary part are 0.0. */
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38 __imag__ result = signbitq (__real__ x) ? PI_LOG10E : 0;
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39 __imag__ result = copysignq (__imag__ result, __imag__ x);
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40 /* Yes, the following line raises an exception. */
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41 __real__ result = -1 / fabsq (__real__ x);
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42 }
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43 else if (__glibc_likely (rcls != QUADFP_NAN && icls != QUADFP_NAN))
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44 {
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45 /* Neither real nor imaginary part is NaN. */
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46 __float128 absx = fabsq (__real__ x), absy = fabsq (__imag__ x);
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47 int scale = 0;
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48
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49 if (absx < absy)
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50 {
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51 __float128 t = absx;
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52 absx = absy;
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53 absy = t;
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54 }
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55
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56 if (absx > FLT128_MAX / 2)
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57 {
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58 scale = -1;
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59 absx = scalbnq (absx, scale);
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60 absy = (absy >= FLT128_MIN * 2 ? scalbnq (absy, scale) : 0);
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61 }
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62 else if (absx < FLT128_MIN && absy < FLT128_MIN)
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63 {
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64 scale = FLT128_MANT_DIG;
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65 absx = scalbnq (absx, scale);
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66 absy = scalbnq (absy, scale);
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67 }
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68
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69 if (absx == 1 && scale == 0)
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70 {
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71 __real__ result = (log1pq (absy * absy)
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72 * ((__float128) M_LOG10Eq / 2));
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73 math_check_force_underflow_nonneg (__real__ result);
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74 }
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75 else if (absx > 1 && absx < 2 && absy < 1 && scale == 0)
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76 {
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77 __float128 d2m1 = (absx - 1) * (absx + 1);
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78 if (absy >= FLT128_EPSILON)
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79 d2m1 += absy * absy;
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80 __real__ result = log1pq (d2m1) * ((__float128) M_LOG10Eq / 2);
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81 }
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82 else if (absx < 1
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83 && absx >= 0.5Q
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84 && absy < FLT128_EPSILON / 2
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85 && scale == 0)
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86 {
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87 __float128 d2m1 = (absx - 1) * (absx + 1);
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88 __real__ result = log1pq (d2m1) * ((__float128) M_LOG10Eq / 2);
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89 }
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90 else if (absx < 1
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91 && absx >= 0.5Q
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92 && scale == 0
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93 && absx * absx + absy * absy >= 0.5Q)
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94 {
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95 __float128 d2m1 = __quadmath_x2y2m1q (absx, absy);
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96 __real__ result = log1pq (d2m1) * ((__float128) M_LOG10Eq / 2);
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97 }
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98 else
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99 {
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100 __float128 d = hypotq (absx, absy);
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101 __real__ result = log10q (d) - scale * LOG10_2;
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102 }
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103
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104 __imag__ result = M_LOG10Eq * atan2q (__imag__ x, __real__ x);
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105 }
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106 else
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107 {
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108 __imag__ result = nanq ("");
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109 if (rcls == QUADFP_INFINITE || icls == QUADFP_INFINITE)
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110 /* Real or imaginary part is infinite. */
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111 __real__ result = HUGE_VALQ;
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112 else
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113 __real__ result = nanq ("");
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114 }
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115
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116 return result;
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117 }
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