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124 lines
3.5 KiB
C
124 lines
3.5 KiB
C
/* Compute complex base 10 logarithm.
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Copyright (C) 1997-2020 Free Software Foundation, Inc.
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This file is part of the GNU C Library.
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Contributed by Ulrich Drepper <drepper@cygnus.com>, 1997.
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The GNU C Library is free software; you can redistribute it and/or
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modify it under the terms of the GNU Lesser General Public
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License as published by the Free Software Foundation; either
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version 2.1 of the License, or (at your option) any later version.
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The GNU C Library is distributed in the hope that it will be useful,
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but WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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Lesser General Public License for more details.
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You should have received a copy of the GNU Lesser General Public
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License along with the GNU C Library; if not, see
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<https://www.gnu.org/licenses/>. */
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#include <complex.h>
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#include <math.h>
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#include <math_private.h>
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#include <math-underflow.h>
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#include <float.h>
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/* log_10 (2). */
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#define LOG10_2 M_LIT (0.3010299956639811952137388947244930267682)
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/* pi * log10 (e). */
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#define PI_LOG10E M_LIT (1.364376353841841347485783625431355770210)
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CFLOAT
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M_DECL_FUNC (__clog10) (CFLOAT x)
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{
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CFLOAT result;
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int rcls = fpclassify (__real__ x);
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int icls = fpclassify (__imag__ x);
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if (__glibc_unlikely (rcls == FP_ZERO && icls == FP_ZERO))
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{
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/* Real and imaginary part are 0.0. */
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__imag__ result = signbit (__real__ x) ? PI_LOG10E : 0;
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__imag__ result = M_COPYSIGN (__imag__ result, __imag__ x);
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/* Yes, the following line raises an exception. */
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__real__ result = -1 / M_FABS (__real__ x);
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}
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else if (__glibc_likely (rcls != FP_NAN && icls != FP_NAN))
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{
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/* Neither real nor imaginary part is NaN. */
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FLOAT absx = M_FABS (__real__ x), absy = M_FABS (__imag__ x);
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int scale = 0;
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if (absx < absy)
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{
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FLOAT t = absx;
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absx = absy;
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absy = t;
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}
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if (absx > M_MAX / 2)
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{
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scale = -1;
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absx = M_SCALBN (absx, scale);
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absy = (absy >= M_MIN * 2 ? M_SCALBN (absy, scale) : 0);
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}
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else if (absx < M_MIN && absy < M_MIN)
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{
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scale = M_MANT_DIG;
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absx = M_SCALBN (absx, scale);
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absy = M_SCALBN (absy, scale);
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}
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if (absx == 1 && scale == 0)
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{
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__real__ result = (M_LOG1P (absy * absy)
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* ((FLOAT) M_MLIT (M_LOG10E) / 2));
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math_check_force_underflow_nonneg (__real__ result);
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}
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else if (absx > 1 && absx < 2 && absy < 1 && scale == 0)
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{
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FLOAT d2m1 = (absx - 1) * (absx + 1);
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if (absy >= M_EPSILON)
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d2m1 += absy * absy;
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__real__ result = M_LOG1P (d2m1) * ((FLOAT) M_MLIT (M_LOG10E) / 2);
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}
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else if (absx < 1
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&& absx >= M_LIT (0.5)
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&& absy < M_EPSILON / 2
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&& scale == 0)
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{
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FLOAT d2m1 = (absx - 1) * (absx + 1);
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__real__ result = M_LOG1P (d2m1) * ((FLOAT) M_MLIT (M_LOG10E) / 2);
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}
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else if (absx < 1
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&& absx >= M_LIT (0.5)
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&& scale == 0
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&& absx * absx + absy * absy >= M_LIT (0.5))
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{
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FLOAT d2m1 = M_SUF (__x2y2m1) (absx, absy);
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__real__ result = M_LOG1P (d2m1) * ((FLOAT) M_MLIT (M_LOG10E) / 2);
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}
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else
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{
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FLOAT d = M_HYPOT (absx, absy);
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__real__ result = M_SUF (__ieee754_log10) (d) - scale * LOG10_2;
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}
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__imag__ result = M_MLIT (M_LOG10E) * M_ATAN2 (__imag__ x, __real__ x);
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}
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else
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{
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__imag__ result = M_NAN;
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if (rcls == FP_INFINITE || icls == FP_INFINITE)
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/* Real or imaginary part is infinite. */
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__real__ result = M_HUGE_VAL;
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else
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__real__ result = M_NAN;
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}
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return result;
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}
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declare_mgen_alias (__clog10, clog10)
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