math/s_clog.c

   1 /* Compute complex natural logarithm.
   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 <complex.h>
  21 #include <math.h>
  22 #include <math_private.h>
  23 #include <float.h>
  24
  25 __complex__ double
  26 __clog (__complex__ double x)
  27 {
  28   __complex__ double result;
  29   int rcls = fpclassify (__real__ x);
  30   int icls = fpclassify (__imag__ x);
  31
  32   if (__builtin_expect (rcls == FP_ZERO && icls == FP_ZERO, 0))
  33     {
  34       /* Real and imaginary part are 0.0.  */
  35       __imag__ result = signbit (__real__ x) ? M_PI : 0.0;
  36       __imag__ result = __copysign (__imag__ result, __imag__ x);
  37       /* Yes, the following line raises an exception.  */
  38       __real__ result = -1.0 / fabs (__real__ x);
  39     }
  40   else if (__builtin_expect (rcls != FP_NAN && icls != FP_NAN, 1))
  41     {
  42       /* Neither real nor imaginary part is NaN.  */
  43       double absx = fabs (__real__ x), absy = fabs (__imag__ x);
  44       double d;
  45       int scale = 0;
  46
  47       if (absx > DBL_MAX / 2.0)
  48         {
  49           scale = -1;
  50           absx = __scalbn (absx, scale);
  51           absy = (absy >= DBL_MIN * 2.0 ? __scalbn (absy, scale) : 0.0);
  52         }
  53       else if (absy > DBL_MAX / 2.0)
  54         {
  55           scale = -1;
  56           absx = (absx >= DBL_MIN * 2.0 ? __scalbn (absx, scale) : 0.0);
  57           absy = __scalbn (absy, scale);
  58         }
  59       else if (absx < DBL_MIN && absy < DBL_MIN)
  60         {
  61           scale = DBL_MANT_DIG;
  62           absx = __scalbn (absx, scale);
  63           absy = __scalbn (absy, scale);
  64         }
  65
  66       d = __ieee754_hypot (absx, absy);
  67
  68       __real__ result = __ieee754_log (d) - scale * M_LN2;
  69       __imag__ result = __ieee754_atan2 (__imag__ x, __real__ x);
  70     }
  71   else
  72     {
  73       __imag__ result = __nan ("");
  74       if (rcls == FP_INFINITE || icls == FP_INFINITE)
  75         /* Real or imaginary part is infinite.  */
  76         __real__ result = HUGE_VAL;
  77       else
  78         __real__ result = __nan ("");
  79     }
  80
  81   return result;
  82 }
  83 weak_alias (__clog, clog)
  84 #ifdef NO_LONG_DOUBLE
  85 strong_alias (__clog, __clogl)
  86 weak_alias (__clog, clogl)
  87 #endif