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192.168.1.100 / T106_DC / aef17607fcd98e0a897542cd02aed0bab0d12eb5 / . / ap / libc / glibc / glibc-2.23 / math / s_clog10.c
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xf.libdd93d52023-05-12 07:10:14 -0700[diff] [blame]1/* Compute complex base 10 logarithm.
2 Copyright (C) 1997-2016 Free Software Foundation, Inc.
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
18 <http://www.gnu.org/licenses/>. */
19
20#include <complex.h>
21#include <math.h>
22#include <math_private.h>
23#include <float.h>
24
25/* log_10 (2). */
26#define M_LOG10_2 0.3010299956639811952137388947244930267682
27
28/* pi * log10 (e). */
29#define M_PI_LOG10E 1.364376353841841347485783625431355770210
30
31__complex__ double
32__clog10 (__complex__ double x)
33{
34 __complex__ double result;
35 int rcls = fpclassify (__real__ x);
36 int icls = fpclassify (__imag__ x);
37
38 if (__glibc_unlikely (rcls == FP_ZERO && icls == FP_ZERO))
39 {
40 /* Real and imaginary part are 0.0. */
41 __imag__ result = signbit (__real__ x) ? M_PI_LOG10E : 0.0;
42 __imag__ result = __copysign (__imag__ result, __imag__ x);
43 /* Yes, the following line raises an exception. */
44 __real__ result = -1.0 / fabs (__real__ x);
45 }
46 else if (__glibc_likely (rcls != FP_NAN && icls != FP_NAN))
47 {
48 /* Neither real nor imaginary part is NaN. */
49 double absx = fabs (__real__ x), absy = fabs (__imag__ x);
50 int scale = 0;
51
52 if (absx < absy)
53 {
54 double t = absx;
55 absx = absy;
56 absy = t;
57 }
58
59 if (absx > DBL_MAX / 2.0)
60 {
61 scale = -1;
62 absx = __scalbn (absx, scale);
63 absy = (absy >= DBL_MIN * 2.0 ? __scalbn (absy, scale) : 0.0);
64 }
65 else if (absx < DBL_MIN && absy < DBL_MIN)
66 {
67 scale = DBL_MANT_DIG;
68 absx = __scalbn (absx, scale);
69 absy = __scalbn (absy, scale);
70 }
71
72 if (absx == 1.0 && scale == 0)
73 {
74 __real__ result = __log1p (absy * absy) * (M_LOG10E / 2.0);
75 math_check_force_underflow_nonneg (__real__ result);
76 }
77 else if (absx > 1.0 && absx < 2.0 && absy < 1.0 && scale == 0)
78 {
79 double d2m1 = (absx - 1.0) * (absx + 1.0);
80 if (absy >= DBL_EPSILON)
81 d2m1 += absy * absy;
82 __real__ result = __log1p (d2m1) * (M_LOG10E / 2.0);
83 }
84 else if (absx < 1.0
85 && absx >= 0.5
86 && absy < DBL_EPSILON / 2.0
87 && scale == 0)
88 {
89 double d2m1 = (absx - 1.0) * (absx + 1.0);
90 __real__ result = __log1p (d2m1) * (M_LOG10E / 2.0);
91 }
92 else if (absx < 1.0
93 && absx >= 0.5
94 && scale == 0
95 && absx * absx + absy * absy >= 0.5)
96 {
97 double d2m1 = __x2y2m1 (absx, absy);
98 __real__ result = __log1p (d2m1) * (M_LOG10E / 2.0);
99 }
100 else
101 {
102 double d = __ieee754_hypot (absx, absy);
103 __real__ result = __ieee754_log10 (d) - scale * M_LOG10_2;
104 }
105
106 __imag__ result = M_LOG10E * __ieee754_atan2 (__imag__ x, __real__ x);
107 }
108 else
109 {
110 __imag__ result = __nan ("");
111 if (rcls == FP_INFINITE || icls == FP_INFINITE)
112 /* Real or imaginary part is infinite. */
113 __real__ result = HUGE_VAL;
114 else
115 __real__ result = __nan ("");
116 }
117
118 return result;
119}
120weak_alias (__clog10, clog10)
121#ifdef NO_LONG_DOUBLE
122strong_alias (__clog10, __clog10l)
123weak_alias (__clog10, clog10l)
124#endif