math/s_clog10_template.c

   1 /* Compute complex base 10 logarithm.
   2    Copyright (C) 1997-2021 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    <https://www.gnu.org/licenses/>.  */
  19
  20 #include <complex.h>
  21 #include <math.h>
  22 #include <math_private.h>
  23 #include <math-underflow.h>
  24 #include <float.h>
  25
  26 /* log_10 (2).  */
  27 #define LOG10_2 M_LIT (0.3010299956639811952137388947244930267682)
  28
  29 /* pi * log10 (e).  */
  30 #define PI_LOG10E M_LIT (1.364376353841841347485783625431355770210)
  31
  32 CFLOAT
  33 M_DECL_FUNC (__clog10) (CFLOAT x)
  34 {
  35   CFLOAT result;
  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.  */
  42       __imag__ result = signbit (__real__ x) ? PI_LOG10E : 0;
  43       __imag__ result = M_COPYSIGN (__imag__ result, __imag__ x);
  44       /* Yes, the following line raises an exception.  */
  45       __real__ result = -1 / M_FABS (__real__ x);
  46     }
  47   else if (__glibc_likely (rcls != FP_NAN && icls != FP_NAN))
  48     {
  49       /* Neither real nor imaginary part is NaN.  */
  50       FLOAT absx = M_FABS (__real__ x), absy = M_FABS (__imag__ x);
  51       int scale = 0;
  52
  53       if (absx < absy)
  54         {
  55           FLOAT t = absx;
  56           absx = absy;
  57           absy = t;
  58         }
  59
  60       if (absx > M_MAX / 2)
  61         {
  62           scale = -1;
  63           absx = M_SCALBN (absx, scale);
  64           absy = (absy >= M_MIN * 2 ? M_SCALBN (absy, scale) : 0);
  65         }
  66       else if (absx < M_MIN && absy < M_MIN)
  67         {
  68           scale = M_MANT_DIG;
  69           absx = M_SCALBN (absx, scale);
  70           absy = M_SCALBN (absy, scale);
  71         }
  72
  73       if (absx == 1 && scale == 0)
  74         {
  75           __real__ result = (M_LOG1P (absy * absy)
  76                              * ((FLOAT) M_MLIT (M_LOG10E) / 2));
  77           math_check_force_underflow_nonneg (__real__ result);
  78         }
  79       else if (absx > 1 && absx < 2 && absy < 1 && scale == 0)
  80         {
  81           FLOAT d2m1 = (absx - 1) * (absx + 1);
  82           if (absy >= M_EPSILON)
  83             d2m1 += absy * absy;
  84           __real__ result = M_LOG1P (d2m1) * ((FLOAT) M_MLIT (M_LOG10E) / 2);
  85         }
  86       else if (absx < 1
  87                && absx >= M_LIT (0.5)
  88                && absy < M_EPSILON / 2
  89                && scale == 0)
  90         {
  91           FLOAT d2m1 = (absx - 1) * (absx + 1);
  92           __real__ result = M_LOG1P (d2m1) * ((FLOAT) M_MLIT (M_LOG10E) / 2);
  93         }
  94       else if (absx < 1
  95                && absx >= M_LIT (0.5)
  96                && scale == 0
  97                && absx * absx + absy * absy >= M_LIT (0.5))
  98         {
  99           FLOAT d2m1 = M_SUF (__x2y2m1) (absx, absy);
 100           __real__ result = M_LOG1P (d2m1) * ((FLOAT) M_MLIT (M_LOG10E) / 2);
 101         }
 102       else
 103         {
 104           FLOAT d = M_HYPOT (absx, absy);
 105           __real__ result = M_SUF (__ieee754_log10) (d) - scale * LOG10_2;
 106         }
 107
 108       __imag__ result = M_MLIT (M_LOG10E) * M_ATAN2 (__imag__ x, __real__ x);
 109     }
 110   else
 111     {
 112       __imag__ result = M_NAN;
 113       if (rcls == FP_INFINITE || icls == FP_INFINITE)
 114         /* Real or imaginary part is infinite.  */
 115         __real__ result = M_HUGE_VAL;
 116       else
 117         __real__ result = M_NAN;
 118     }
 119
 120   return result;
 121 }
 122
 123 declare_mgen_alias (__clog10, clog10)