math/s_clog10_template.c

   1 /* Compute complex base 10 logarithm.
   2    Copyright (C) 1997-2022 Free Software Foundation, Inc.
   3    This file is part of the GNU C Library.
   4
   5    The GNU C Library is free software; you can redistribute it and/or
   6    modify it under the terms of the GNU Lesser General Public
   7    License as published by the Free Software Foundation; either
   8    version 2.1 of the License, or (at your option) any later version.
   9
  10    The GNU C Library is distributed in the hope that it will be useful,
  11    but WITHOUT ANY WARRANTY; without even the implied warranty of
  12    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  13    Lesser General Public License for more details.
  14
  15    You should have received a copy of the GNU Lesser General Public
  16    License along with the GNU C Library; if not, see
  17    <https://www.gnu.org/licenses/>.  */
  18
  19 #include <complex.h>
  20 #include <math.h>
  21 #include <math_private.h>
  22 #include <math-underflow.h>
  23 #include <float.h>
  24
  25 /* log_10 (2).  */
  26 #define LOG10_2 M_LIT (0.3010299956639811952137388947244930267682)
  27
  28 /* pi * log10 (e).  */
  29 #define PI_LOG10E M_LIT (1.364376353841841347485783625431355770210)
  30
  31 CFLOAT
  32 M_DECL_FUNC (__clog10) (CFLOAT x)
  33 {
  34   CFLOAT 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) ? PI_LOG10E : 0;
  42       __imag__ result = M_COPYSIGN (__imag__ result, __imag__ x);
  43       /* Yes, the following line raises an exception.  */
  44       __real__ result = -1 / M_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       FLOAT absx = M_FABS (__real__ x), absy = M_FABS (__imag__ x);
  50       int scale = 0;
  51
  52       if (absx < absy)
  53         {
  54           FLOAT t = absx;
  55           absx = absy;
  56           absy = t;
  57         }
  58
  59       if (absx > M_MAX / 2)
  60         {
  61           scale = -1;
  62           absx = M_SCALBN (absx, scale);
  63           absy = (absy >= M_MIN * 2 ? M_SCALBN (absy, scale) : 0);
  64         }
  65       else if (absx < M_MIN && absy < M_MIN)
  66         {
  67           scale = M_MANT_DIG;
  68           absx = M_SCALBN (absx, scale);
  69           absy = M_SCALBN (absy, scale);
  70         }
  71
  72       if (absx == 1 && scale == 0)
  73         {
  74           __real__ result = (M_LOG1P (absy * absy)
  75                              * (M_MLIT (M_LOG10E) / 2));
  76           math_check_force_underflow_nonneg (__real__ result);
  77         }
  78       else if (absx > 1 && absx < 2 && absy < 1 && scale == 0)
  79         {
  80           FLOAT d2m1 = (absx - 1) * (absx + 1);
  81           if (absy >= M_EPSILON)
  82             d2m1 += absy * absy;
  83           __real__ result = M_LOG1P (d2m1) * (M_MLIT (M_LOG10E) / 2);
  84         }
  85       else if (absx < 1
  86                && absx >= M_LIT (0.5)
  87                && absy < M_EPSILON / 2
  88                && scale == 0)
  89         {
  90           FLOAT d2m1 = (absx - 1) * (absx + 1);
  91           __real__ result = M_LOG1P (d2m1) * (M_MLIT (M_LOG10E) / 2);
  92         }
  93       else if (absx < 1
  94                && absx >= M_LIT (0.5)
  95                && scale == 0
  96                && absx * absx + absy * absy >= M_LIT (0.5))
  97         {
  98           FLOAT d2m1 = M_SUF (__x2y2m1) (absx, absy);
  99           __real__ result = M_LOG1P (d2m1) * (M_MLIT (M_LOG10E) / 2);
 100         }
 101       else
 102         {
 103           FLOAT d = M_HYPOT (absx, absy);
 104           __real__ result = M_SUF (__ieee754_log10) (d) - scale * LOG10_2;
 105         }
 106
 107       __imag__ result = M_MLIT (M_LOG10E) * M_ATAN2 (__imag__ x, __real__ x);
 108     }
 109   else
 110     {
 111       __imag__ result = M_NAN;
 112       if (rcls == FP_INFINITE || icls == FP_INFINITE)
 113         /* Real or imaginary part is infinite.  */
 114         __real__ result = M_HUGE_VAL;
 115       else
 116         __real__ result = M_NAN;
 117     }
 118
 119   return result;
 120 }
 121
 122 declare_mgen_alias (__clog10, clog10)