math/s_clog_template.c

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