libquadmath/math/clog10q.c

   1 /* Compute complex base 10 logarithm for complex __float128.
   2    Copyright (C) 1997-2012 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
  23 /* log_10 (2).  */
  24 #define M_LOG10_2q 0.3010299956639811952137388947244930267682Q
  25
  26
  27 __complex128
  28 clog10q (__complex128 x)
  29 {
  30   __complex128 result;
  31   int rcls = fpclassifyq (__real__ x);
  32   int icls = fpclassifyq (__imag__ x);
  33
  34   if (__builtin_expect (rcls == QUADFP_ZERO && icls == QUADFP_ZERO, 0))
  35     {
  36       /* Real and imaginary part are 0.0.  */
  37       __imag__ result = signbitq (__real__ x) ? M_PIq : 0.0Q;
  38       __imag__ result = copysignq (__imag__ result, __imag__ x);
  39       /* Yes, the following line raises an exception.  */
  40       __real__ result = -1.0Q / fabsq (__real__ x);
  41     }
  42   else if (__builtin_expect (rcls != QUADFP_NAN && icls != QUADFP_NAN, 1))
  43     {
  44       /* Neither real nor imaginary part is NaN.  */
  45       __float128 absx = fabsq (__real__ x), absy = fabsq (__imag__ x);
  46       int scale = 0;
  47
  48       if (absx < absy)
  49         {
  50           __float128 t = absx;
  51           absx = absy;
  52           absy = t;
  53         }
  54
  55       if (absx > FLT128_MAX / 2.0Q)
  56         {
  57           scale = -1;
  58           absx = scalbnq (absx, scale);
  59           absy = (absy >= FLT128_MIN * 2.0Q ? scalbnq (absy, scale) : 0.0Q);
  60         }
  61       else if (absx < FLT128_MIN && absy < FLT128_MIN)
  62         {
  63           scale = FLT128_MANT_DIG;
  64           absx = scalbnq (absx, scale);
  65           absy = scalbnq (absy, scale);
  66         }
  67
  68       if (absx == 1.0Q && scale == 0)
  69         {
  70           __float128 absy2 = absy * absy;
  71           if (absy2 <= FLT128_MIN * 2.0Q * M_LN10q)
  72             __real__ result
  73               = (absy2 / 2.0Q - absy2 * absy2 / 4.0Q) * M_LOG10Eq;
  74           else
  75             __real__ result = log1pq (absy2) * (M_LOG10Eq / 2.0Q);
  76         }
  77       else if (absx > 1.0Q && absx < 2.0Q && absy < 1.0Q && scale == 0)
  78         {
  79           __float128 d2m1 = (absx - 1.0Q) * (absx + 1.0Q);
  80           if (absy >= FLT128_EPSILON)
  81             d2m1 += absy * absy;
  82           __real__ result = log1pq (d2m1) * (M_LOG10Eq / 2.0Q);
  83         }
  84       else if (absx < 1.0Q
  85                && absx >= 0.75Q
  86                && absy < FLT128_EPSILON / 2.0Q
  87                && scale == 0)
  88         {
  89           __float128 d2m1 = (absx - 1.0Q) * (absx + 1.0Q);
  90           __real__ result = log1pq (d2m1) * (M_LOG10Eq / 2.0Q);
  91         }
  92       else if (absx < 1.0Q && (absx >= 0.75Q || absy >= 0.5Q) && scale == 0)
  93         {
  94           __float128 d2m1 = __quadmath_x2y2m1q (absx, absy);
  95           __real__ result = log1pq (d2m1) * (M_LOG10Eq / 2.0Q);
  96         }
  97       else
  98         {
  99           __float128 d = hypotq (absx, absy);
 100           __real__ result = log10q (d) - scale * M_LOG10_2q;
 101         }
 102
 103       __imag__ result = M_LOG10Eq * atan2q (__imag__ x, __real__ x);
 104     }
 105   else
 106     {
 107       __imag__ result = nanq ("");
 108       if (rcls == QUADFP_INFINITE || icls == QUADFP_INFINITE)
 109         /* Real or imaginary part is infinite.  */
 110         __real__ result = HUGE_VALQ;
 111       else
 112         __real__ result = nanq ("");
 113     }
 114
 115   return result;
 116 }