libquadmath/math/clog10q.c

   1 /* Compute complex base 10 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 /* log_10 (2).  */
  23 #define LOG10_2 0.3010299956639811952137388947244930267682Q
  24
  25 /* pi * log10 (e).  */
  26 #define PI_LOG10E 1.364376353841841347485783625431355770210Q
  27
  28 __complex128
  29 clog10q (__complex128 x)
  30 {
  31   __complex128 result;
  32   int rcls = fpclassifyq (__real__ x);
  33   int icls = fpclassifyq (__imag__ x);
  34
  35   if (__glibc_unlikely (rcls == QUADFP_ZERO && icls == QUADFP_ZERO))
  36     {
  37       /* Real and imaginary part are 0.0.  */
  38       __imag__ result = signbitq (__real__ x) ? PI_LOG10E : 0;
  39       __imag__ result = copysignq (__imag__ result, __imag__ x);
  40       /* Yes, the following line raises an exception.  */
  41       __real__ result = -1 / fabsq (__real__ x);
  42     }
  43   else if (__glibc_likely (rcls != QUADFP_NAN && icls != QUADFP_NAN))
  44     {
  45       /* Neither real nor imaginary part is NaN.  */
  46       __float128 absx = fabsq (__real__ x), absy = fabsq (__imag__ x);
  47       int scale = 0;
  48
  49       if (absx < absy)
  50         {
  51           __float128 t = absx;
  52           absx = absy;
  53           absy = t;
  54         }
  55
  56       if (absx > FLT128_MAX / 2)
  57         {
  58           scale = -1;
  59           absx = scalbnq (absx, scale);
  60           absy = (absy >= FLT128_MIN * 2 ? scalbnq (absy, scale) : 0);
  61         }
  62       else if (absx < FLT128_MIN && absy < FLT128_MIN)
  63         {
  64           scale = FLT128_MANT_DIG;
  65           absx = scalbnq (absx, scale);
  66           absy = scalbnq (absy, scale);
  67         }
  68
  69       if (absx == 1 && scale == 0)
  70         {
  71           __real__ result = (log1pq (absy * absy)
  72                              * ((__float128) M_LOG10Eq / 2));
  73           math_check_force_underflow_nonneg (__real__ result);
  74         }
  75       else if (absx > 1 && absx < 2 && absy < 1 && scale == 0)
  76         {
  77           __float128 d2m1 = (absx - 1) * (absx + 1);
  78           if (absy >= FLT128_EPSILON)
  79             d2m1 += absy * absy;
  80           __real__ result = log1pq (d2m1) * ((__float128) M_LOG10Eq / 2);
  81         }
  82       else if (absx < 1
  83                && absx >= 0.5Q
  84                && absy < FLT128_EPSILON / 2
  85                && scale == 0)
  86         {
  87           __float128 d2m1 = (absx - 1) * (absx + 1);
  88           __real__ result = log1pq (d2m1) * ((__float128) M_LOG10Eq / 2);
  89         }
  90       else if (absx < 1
  91                && absx >= 0.5Q
  92                && scale == 0
  93                && absx * absx + absy * absy >= 0.5Q)
  94         {
  95           __float128 d2m1 = __quadmath_x2y2m1q (absx, absy);
  96           __real__ result = log1pq (d2m1) * ((__float128) M_LOG10Eq / 2);
  97         }
  98       else
  99         {
 100           __float128 d = hypotq (absx, absy);
 101           __real__ result = log10q (d) - scale * LOG10_2;
 102         }
 103
 104       __imag__ result = M_LOG10Eq * atan2q (__imag__ x, __real__ x);
 105     }
 106   else
 107     {
 108       __imag__ result = nanq ("");
 109       if (rcls == QUADFP_INFINITE || icls == QUADFP_INFINITE)
 110         /* Real or imaginary part is infinite.  */
 111         __real__ result = HUGE_VALQ;
 112       else
 113         __real__ result = nanq ("");
 114     }
 115
 116   return result;
 117 }