math/s_clog10.c

   1 /* Compute complex base 10 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 /* log_10 (2).  */
  26 #define M_LOG10_2 0.3010299956639811952137388947244930267682
  27
  28 __complex__ double
  29 __clog10 (__complex__ double x)
  30 {
  31   __complex__ double result;
  32   int rcls = fpclassify (__real__ x);
  33   int icls = fpclassify (__imag__ x);
  34
  35   if (__builtin_expect (rcls == FP_ZERO && icls == FP_ZERO, 0))
  36     {
  37       /* Real and imaginary part are 0.0.  */
  38       __imag__ result = signbit (__real__ x) ? M_PI : 0.0;
  39       __imag__ result = __copysign (__imag__ result, __imag__ x);
  40       /* Yes, the following line raises an exception.  */
  41       __real__ result = -1.0 / fabs (__real__ x);
  42     }
  43   else if (__builtin_expect (rcls != FP_NAN && icls != FP_NAN, 1))
  44     {
  45       /* Neither real nor imaginary part is NaN.  */
  46       double d;
  47       int scale = 0;
  48
  49       if (fabs (__real__ x) > DBL_MAX / 2.0
  50           || fabs (__imag__ x) > DBL_MAX / 2.0)
  51         {
  52           scale = -1;
  53           __real__ x = __scalbn (__real__ x, scale);
  54           __imag__ x = __scalbn (__imag__ x, scale);
  55         }
  56       else if (fabs (__real__ x) < DBL_MIN
  57                && fabs (__imag__ x) < DBL_MIN)
  58         {
  59           scale = DBL_MANT_DIG;
  60           __real__ x = __scalbn (__real__ x, scale);
  61           __imag__ x = __scalbn (__imag__ x, scale);
  62         }
  63
  64       d = __ieee754_hypot (__real__ x, __imag__ x);
  65
  66       __real__ result = __ieee754_log10 (d) - scale * M_LOG10_2;
  67       __imag__ result = M_LOG10E * __ieee754_atan2 (__imag__ x, __real__ x);
  68     }
  69   else
  70     {
  71       __imag__ result = __nan ("");
  72       if (rcls == FP_INFINITE || icls == FP_INFINITE)
  73         /* Real or imaginary part is infinite.  */
  74         __real__ result = HUGE_VAL;
  75       else
  76         __real__ result = __nan ("");
  77     }
  78
  79   return result;
  80 }
  81 weak_alias (__clog10, clog10)
  82 #ifdef NO_LONG_DOUBLE
  83 strong_alias (__clog10, __clog10l)
  84 weak_alias (__clog10, clog10l)
  85 #endif