math/s_clog_template.c

   1 /* Compute complex natural logarithm.
   2    Copyright (C) 1997-2024 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 CFLOAT
  26 M_DECL_FUNC (__clog) (CFLOAT x)
  27 {
  28   CFLOAT result;
  29   int rcls = fpclassify (__real__ x);
  30   int icls = fpclassify (__imag__ x);
  31
  32   if (__glibc_unlikely (rcls == FP_ZERO && icls == FP_ZERO))
  33     {
  34       /* Real and imaginary part are 0.0.  */
  35       __imag__ result = signbit (__real__ x) ? M_MLIT (M_PI) : 0;
  36       __imag__ result = M_COPYSIGN (__imag__ result, __imag__ x);
  37       /* Yes, the following line raises an exception.  */
  38       __real__ result = -1 / M_FABS (__real__ x);
  39     }
  40   else if (__glibc_likely (rcls != FP_NAN && icls != FP_NAN))
  41     {
  42       /* Neither real nor imaginary part is NaN.  */
  43       FLOAT absx = M_FABS (__real__ x), absy = M_FABS (__imag__ x);
  44       int scale = 0;
  45
  46       if (absx < absy)
  47         {
  48           FLOAT t = absx;
  49           absx = absy;
  50           absy = t;
  51         }
  52
  53       if (absx > M_MAX / 2)
  54         {
  55           scale = -1;
  56           absx = M_SCALBN (absx, scale);
  57           absy = (absy >= M_MIN * 2 ? M_SCALBN (absy, scale) : 0);
  58         }
  59       else if (absx < M_MIN && absy < M_MIN)
  60         {
  61           scale = M_MANT_DIG;
  62           absx = M_SCALBN (absx, scale);
  63           absy = M_SCALBN (absy, scale);
  64         }
  65
  66       if (absx == 1 && scale == 0)
  67         {
  68           __real__ result = M_LOG1P (absy * absy) / 2;
  69           math_check_force_underflow_nonneg (__real__ result);
  70         }
  71       else if (absx > 1 && absx < 2 && absy < 1 && scale == 0)
  72         {
  73           FLOAT d2m1 = (absx - 1) * (absx + 1);
  74           if (absy >= M_EPSILON)
  75             d2m1 += absy * absy;
  76           __real__ result = M_LOG1P (d2m1) / 2;
  77         }
  78       else if (absx < 1
  79                && absx >= M_LIT (0.5)
  80                && absy < M_EPSILON / 2
  81                && scale == 0)
  82         {
  83           FLOAT d2m1 = (absx - 1) * (absx + 1);
  84           __real__ result = M_LOG1P (d2m1) / 2;
  85         }
  86       else if (absx < 1
  87                && absx >= M_LIT (0.5)
  88                && scale == 0
  89                && absx * absx + absy * absy >= M_LIT (0.5))
  90         {
  91           FLOAT d2m1 = M_SUF (__x2y2m1) (absx, absy);
  92           __real__ result = M_LOG1P (d2m1) / 2;
  93         }
  94       else
  95         {
  96           FLOAT d = M_HYPOT (absx, absy);
  97           __real__ result = M_LOG (d) - scale * M_MLIT (M_LN2);
  98         }
  99
 100       __imag__ result = M_ATAN2 (__imag__ x, __real__ x);
 101     }
 102   else
 103     {
 104       __imag__ result = M_NAN;
 105       if (rcls == FP_INFINITE || icls == FP_INFINITE)
 106         /* Real or imaginary part is infinite.  */
 107         __real__ result = M_HUGE_VAL;
 108       else
 109         __real__ result = M_NAN;
 110     }
 111
 112   return result;
 113 }
 114
 115 declare_mgen_alias (__clog, clog)