libquadmath/math/clogq.c

   1 /* Compute complex natural logarithm.
   2    Copyright (C) 1997-2018 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    <http://www.gnu.org/licenses/>.  */
  19
  20 #include "quadmath-imp.h"
  21
  22 __complex128
  23 clogq (__complex128 x)
  24 {
  25   __complex128 result;
  26   int rcls = fpclassifyq (__real__ x);
  27   int icls = fpclassifyq (__imag__ x);
  28
  29   if (__glibc_unlikely (rcls == QUADFP_ZERO && icls == QUADFP_ZERO))
  30     {
  31       /* Real and imaginary part are 0.0.  */
  32       __imag__ result = signbitq (__real__ x) ? (__float128) M_PIq : 0;
  33       __imag__ result = copysignq (__imag__ result, __imag__ x);
  34       /* Yes, the following line raises an exception.  */
  35       __real__ result = -1 / fabsq (__real__ x);
  36     }
  37   else if (__glibc_likely (rcls != QUADFP_NAN && icls != QUADFP_NAN))
  38     {
  39       /* Neither real nor imaginary part is NaN.  */
  40       __float128 absx = fabsq (__real__ x), absy = fabsq (__imag__ x);
  41       int scale = 0;
  42
  43       if (absx < absy)
  44         {
  45           __float128 t = absx;
  46           absx = absy;
  47           absy = t;
  48         }
  49
  50       if (absx > FLT128_MAX / 2)
  51         {
  52           scale = -1;
  53           absx = scalbnq (absx, scale);
  54           absy = (absy >= FLT128_MIN * 2 ? scalbnq (absy, scale) : 0);
  55         }
  56       else if (absx < FLT128_MIN && absy < FLT128_MIN)
  57         {
  58           scale = FLT128_MANT_DIG;
  59           absx = scalbnq (absx, scale);
  60           absy = scalbnq (absy, scale);
  61         }
  62
  63       if (absx == 1 && scale == 0)
  64         {
  65           __real__ result = log1pq (absy * absy) / 2;
  66           math_check_force_underflow_nonneg (__real__ result);
  67         }
  68       else if (absx > 1 && absx < 2 && absy < 1 && scale == 0)
  69         {
  70           __float128 d2m1 = (absx - 1) * (absx + 1);
  71           if (absy >= FLT128_EPSILON)
  72             d2m1 += absy * absy;
  73           __real__ result = log1pq (d2m1) / 2;
  74         }
  75       else if (absx < 1
  76                && absx >= 0.5Q
  77                && absy < FLT128_EPSILON / 2
  78                && scale == 0)
  79         {
  80           __float128 d2m1 = (absx - 1) * (absx + 1);
  81           __real__ result = log1pq (d2m1) / 2;
  82         }
  83       else if (absx < 1
  84                && absx >= 0.5Q
  85                && scale == 0
  86                && absx * absx + absy * absy >= 0.5Q)
  87         {
  88           __float128 d2m1 = __quadmath_x2y2m1q (absx, absy);
  89           __real__ result = log1pq (d2m1) / 2;
  90         }
  91       else
  92         {
  93           __float128 d = hypotq (absx, absy);
  94           __real__ result = logq (d) - scale * (__float128) M_LN2q;
  95         }
  96
  97       __imag__ result = atan2q (__imag__ x, __real__ x);
  98     }
  99   else
 100     {
 101       __imag__ result = nanq ("");
 102       if (rcls == QUADFP_INFINITE || icls == QUADFP_INFINITE)
 103         /* Real or imaginary part is infinite.  */
 104         __real__ result = HUGE_VALQ;
 105       else
 106         __real__ result = nanq ("");
 107     }
 108
 109   return result;
 110 }