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1dbc54f6 | 1 | /* Compute complex base 10 logarithm. |
2b778ceb | 2 | Copyright (C) 1997-2021 Free Software Foundation, Inc. |
1dbc54f6 PM |
3 | This file is part of the GNU C Library. |
4 | Contributed by Ulrich Drepper <drepper@cygnus.com>, 1997. | |
5 | ||
6 | The GNU C Library is free software; you can redistribute it and/or | |
7 | modify it under the terms of the GNU Lesser General Public | |
8 | License as published by the Free Software Foundation; either | |
9 | version 2.1 of the License, or (at your option) any later version. | |
10 | ||
11 | The GNU C Library is distributed in the hope that it will be useful, | |
12 | but WITHOUT ANY WARRANTY; without even the implied warranty of | |
13 | MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU | |
14 | Lesser General Public License for more details. | |
15 | ||
16 | You should have received a copy of the GNU Lesser General Public | |
17 | License along with the GNU C Library; if not, see | |
5a82c748 | 18 | <https://www.gnu.org/licenses/>. */ |
1dbc54f6 PM |
19 | |
20 | #include <complex.h> | |
21 | #include <math.h> | |
22 | #include <math_private.h> | |
8f5b00d3 | 23 | #include <math-underflow.h> |
1dbc54f6 PM |
24 | #include <float.h> |
25 | ||
26 | /* log_10 (2). */ | |
feb62dda | 27 | #define LOG10_2 M_LIT (0.3010299956639811952137388947244930267682) |
1dbc54f6 PM |
28 | |
29 | /* pi * log10 (e). */ | |
feb62dda | 30 | #define PI_LOG10E M_LIT (1.364376353841841347485783625431355770210) |
1dbc54f6 | 31 | |
feb62dda PM |
32 | CFLOAT |
33 | M_DECL_FUNC (__clog10) (CFLOAT x) | |
1dbc54f6 | 34 | { |
feb62dda | 35 | CFLOAT result; |
1dbc54f6 PM |
36 | int rcls = fpclassify (__real__ x); |
37 | int icls = fpclassify (__imag__ x); | |
38 | ||
39 | if (__glibc_unlikely (rcls == FP_ZERO && icls == FP_ZERO)) | |
40 | { | |
41 | /* Real and imaginary part are 0.0. */ | |
feb62dda PM |
42 | __imag__ result = signbit (__real__ x) ? PI_LOG10E : 0; |
43 | __imag__ result = M_COPYSIGN (__imag__ result, __imag__ x); | |
1dbc54f6 | 44 | /* Yes, the following line raises an exception. */ |
feb62dda | 45 | __real__ result = -1 / M_FABS (__real__ x); |
1dbc54f6 PM |
46 | } |
47 | else if (__glibc_likely (rcls != FP_NAN && icls != FP_NAN)) | |
48 | { | |
49 | /* Neither real nor imaginary part is NaN. */ | |
feb62dda | 50 | FLOAT absx = M_FABS (__real__ x), absy = M_FABS (__imag__ x); |
1dbc54f6 PM |
51 | int scale = 0; |
52 | ||
53 | if (absx < absy) | |
54 | { | |
feb62dda | 55 | FLOAT t = absx; |
1dbc54f6 PM |
56 | absx = absy; |
57 | absy = t; | |
58 | } | |
59 | ||
feb62dda | 60 | if (absx > M_MAX / 2) |
1dbc54f6 PM |
61 | { |
62 | scale = -1; | |
feb62dda PM |
63 | absx = M_SCALBN (absx, scale); |
64 | absy = (absy >= M_MIN * 2 ? M_SCALBN (absy, scale) : 0); | |
1dbc54f6 | 65 | } |
feb62dda | 66 | else if (absx < M_MIN && absy < M_MIN) |
1dbc54f6 | 67 | { |
feb62dda PM |
68 | scale = M_MANT_DIG; |
69 | absx = M_SCALBN (absx, scale); | |
70 | absy = M_SCALBN (absy, scale); | |
1dbc54f6 PM |
71 | } |
72 | ||
feb62dda | 73 | if (absx == 1 && scale == 0) |
1dbc54f6 | 74 | { |
feb62dda PM |
75 | __real__ result = (M_LOG1P (absy * absy) |
76 | * ((FLOAT) M_MLIT (M_LOG10E) / 2)); | |
1dbc54f6 PM |
77 | math_check_force_underflow_nonneg (__real__ result); |
78 | } | |
feb62dda | 79 | else if (absx > 1 && absx < 2 && absy < 1 && scale == 0) |
1dbc54f6 | 80 | { |
feb62dda PM |
81 | FLOAT d2m1 = (absx - 1) * (absx + 1); |
82 | if (absy >= M_EPSILON) | |
1dbc54f6 | 83 | d2m1 += absy * absy; |
feb62dda | 84 | __real__ result = M_LOG1P (d2m1) * ((FLOAT) M_MLIT (M_LOG10E) / 2); |
1dbc54f6 | 85 | } |
feb62dda PM |
86 | else if (absx < 1 |
87 | && absx >= M_LIT (0.5) | |
88 | && absy < M_EPSILON / 2 | |
1dbc54f6 PM |
89 | && scale == 0) |
90 | { | |
feb62dda PM |
91 | FLOAT d2m1 = (absx - 1) * (absx + 1); |
92 | __real__ result = M_LOG1P (d2m1) * ((FLOAT) M_MLIT (M_LOG10E) / 2); | |
1dbc54f6 | 93 | } |
feb62dda PM |
94 | else if (absx < 1 |
95 | && absx >= M_LIT (0.5) | |
1dbc54f6 | 96 | && scale == 0 |
feb62dda | 97 | && absx * absx + absy * absy >= M_LIT (0.5)) |
1dbc54f6 | 98 | { |
feb62dda PM |
99 | FLOAT d2m1 = M_SUF (__x2y2m1) (absx, absy); |
100 | __real__ result = M_LOG1P (d2m1) * ((FLOAT) M_MLIT (M_LOG10E) / 2); | |
1dbc54f6 PM |
101 | } |
102 | else | |
103 | { | |
feb62dda PM |
104 | FLOAT d = M_HYPOT (absx, absy); |
105 | __real__ result = M_SUF (__ieee754_log10) (d) - scale * LOG10_2; | |
1dbc54f6 PM |
106 | } |
107 | ||
feb62dda | 108 | __imag__ result = M_MLIT (M_LOG10E) * M_ATAN2 (__imag__ x, __real__ x); |
1dbc54f6 PM |
109 | } |
110 | else | |
111 | { | |
feb62dda | 112 | __imag__ result = M_NAN; |
1dbc54f6 PM |
113 | if (rcls == FP_INFINITE || icls == FP_INFINITE) |
114 | /* Real or imaginary part is infinite. */ | |
feb62dda | 115 | __real__ result = M_HUGE_VAL; |
1dbc54f6 | 116 | else |
feb62dda | 117 | __real__ result = M_NAN; |
1dbc54f6 PM |
118 | } |
119 | ||
120 | return result; | |
121 | } | |
feb62dda PM |
122 | |
123 | declare_mgen_alias (__clog10, clog10) |