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/* Compute complex base 10 logarithm.
Copyright (C) 1997-2023 Free Software Foundation, Inc.
This file is part of the GNU C Library.
The GNU C Library is free software; you can redistribute it and/or
modify it under the terms of the GNU Lesser General Public
License as published by the Free Software Foundation; either
version 2.1 of the License, or (at your option) any later version.
The GNU C Library is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
Lesser General Public License for more details.
You should have received a copy of the GNU Lesser General Public
License along with the GNU C Library; if not, see
<https://www.gnu.org/licenses/>. */
#include <complex.h>
#include <math.h>
#include <math_private.h>
#include <math-underflow.h>
#include <float.h>
/* log_10 (2). */
#define LOG10_2 M_LIT (0.3010299956639811952137388947244930267682)
/* pi * log10 (e). */
#define PI_LOG10E M_LIT (1.364376353841841347485783625431355770210)
CFLOAT
M_DECL_FUNC (__clog10) (CFLOAT x)
{
CFLOAT result;
int rcls = fpclassify (__real__ x);
int icls = fpclassify (__imag__ x);
if (__glibc_unlikely (rcls == FP_ZERO && icls == FP_ZERO))
{
/* Real and imaginary part are 0.0. */
__imag__ result = signbit (__real__ x) ? PI_LOG10E : 0;
__imag__ result = M_COPYSIGN (__imag__ result, __imag__ x);
/* Yes, the following line raises an exception. */
__real__ result = -1 / M_FABS (__real__ x);
}
else if (__glibc_likely (rcls != FP_NAN && icls != FP_NAN))
{
/* Neither real nor imaginary part is NaN. */
FLOAT absx = M_FABS (__real__ x), absy = M_FABS (__imag__ x);
int scale = 0;
if (absx < absy)
{
FLOAT t = absx;
absx = absy;
absy = t;
}
if (absx > M_MAX / 2)
{
scale = -1;
absx = M_SCALBN (absx, scale);
absy = (absy >= M_MIN * 2 ? M_SCALBN (absy, scale) : 0);
}
else if (absx < M_MIN && absy < M_MIN)
{
scale = M_MANT_DIG;
absx = M_SCALBN (absx, scale);
absy = M_SCALBN (absy, scale);
}
if (absx == 1 && scale == 0)
{
__real__ result = (M_LOG1P (absy * absy)
* (M_MLIT (M_LOG10E) / 2));
math_check_force_underflow_nonneg (__real__ result);
}
else if (absx > 1 && absx < 2 && absy < 1 && scale == 0)
{
FLOAT d2m1 = (absx - 1) * (absx + 1);
if (absy >= M_EPSILON)
d2m1 += absy * absy;
__real__ result = M_LOG1P (d2m1) * (M_MLIT (M_LOG10E) / 2);
}
else if (absx < 1
&& absx >= M_LIT (0.5)
&& absy < M_EPSILON / 2
&& scale == 0)
{
FLOAT d2m1 = (absx - 1) * (absx + 1);
__real__ result = M_LOG1P (d2m1) * (M_MLIT (M_LOG10E) / 2);
}
else if (absx < 1
&& absx >= M_LIT (0.5)
&& scale == 0
&& absx * absx + absy * absy >= M_LIT (0.5))
{
FLOAT d2m1 = M_SUF (__x2y2m1) (absx, absy);
__real__ result = M_LOG1P (d2m1) * (M_MLIT (M_LOG10E) / 2);
}
else
{
FLOAT d = M_HYPOT (absx, absy);
__real__ result = M_SUF (__ieee754_log10) (d) - scale * LOG10_2;
}
__imag__ result = M_MLIT (M_LOG10E) * M_ATAN2 (__imag__ x, __real__ x);
}
else
{
__imag__ result = M_NAN;
if (rcls == FP_INFINITE || icls == FP_INFINITE)
/* Real or imaginary part is infinite. */
__real__ result = M_HUGE_VAL;
else
__real__ result = M_NAN;
}
return result;
}
declare_mgen_alias (__clog10, clog10)
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