math/s_clog10l.c

   1 /* Compute complex base 10 logarithm.
   2    Copyright (C) 1997-2014 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 /* To avoid spurious underflows, use this definition to treat IBM long
  26    double as approximating an IEEE-style format.  */
  27 #if LDBL_MANT_DIG == 106
  28 # undef LDBL_EPSILON
  29 # define LDBL_EPSILON 0x1p-106L
  30 #endif
  31
  32 /* log_10 (2).  */
  33 #define M_LOG10_2l 0.3010299956639811952137388947244930267682L
  34
  35 __complex__ long double
  36 __clog10l (__complex__ long double x)
  37 {
  38   __complex__ long double result;
  39   int rcls = fpclassify (__real__ x);
  40   int icls = fpclassify (__imag__ x);
  41
  42   if (__glibc_unlikely (rcls == FP_ZERO && icls == FP_ZERO))
  43     {
  44       /* Real and imaginary part are 0.0.  */
  45       __imag__ result = signbit (__real__ x) ? M_PIl : 0.0;
  46       __imag__ result = __copysignl (__imag__ result, __imag__ x);
  47       /* Yes, the following line raises an exception.  */
  48       __real__ result = -1.0 / fabsl (__real__ x);
  49     }
  50   else if (__glibc_likely (rcls != FP_NAN && icls != FP_NAN))
  51     {
  52       /* Neither real nor imaginary part is NaN.  */
  53       long double absx = fabsl (__real__ x), absy = fabsl (__imag__ x);
  54       int scale = 0;
  55
  56       if (absx < absy)
  57         {
  58           long double t = absx;
  59           absx = absy;
  60           absy = t;
  61         }
  62
  63       if (absx > LDBL_MAX / 2.0L)
  64         {
  65           scale = -1;
  66           absx = __scalbnl (absx, scale);
  67           absy = (absy >= LDBL_MIN * 2.0L ? __scalbnl (absy, scale) : 0.0L);
  68         }
  69       else if (absx < LDBL_MIN && absy < LDBL_MIN)
  70         {
  71           scale = LDBL_MANT_DIG;
  72           absx = __scalbnl (absx, scale);
  73           absy = __scalbnl (absy, scale);
  74         }
  75
  76       if (absx == 1.0L && scale == 0)
  77         {
  78           long double absy2 = absy * absy;
  79           if (absy2 <= LDBL_MIN * 2.0L * M_LN10l)
  80             __real__ result
  81               = (absy2 / 2.0L - absy2 * absy2 / 4.0L) * M_LOG10El;
  82           else
  83             __real__ result = __log1pl (absy2) * (M_LOG10El / 2.0L);
  84         }
  85       else if (absx > 1.0L && absx < 2.0L && absy < 1.0L && scale == 0)
  86         {
  87           long double d2m1 = (absx - 1.0L) * (absx + 1.0L);
  88           if (absy >= LDBL_EPSILON)
  89             d2m1 += absy * absy;
  90           __real__ result = __log1pl (d2m1) * (M_LOG10El / 2.0L);
  91         }
  92       else if (absx < 1.0L
  93                && absx >= 0.75L
  94                && absy < LDBL_EPSILON / 2.0L
  95                && scale == 0)
  96         {
  97           long double d2m1 = (absx - 1.0L) * (absx + 1.0L);
  98           __real__ result = __log1pl (d2m1) * (M_LOG10El / 2.0L);
  99         }
 100       else if (absx < 1.0L && (absx >= 0.75L || absy >= 0.5L) && scale == 0)
 101         {
 102           long double d2m1 = __x2y2m1l (absx, absy);
 103           __real__ result = __log1pl (d2m1) * (M_LOG10El / 2.0L);
 104         }
 105       else
 106         {
 107           long double d = __ieee754_hypotl (absx, absy);
 108           __real__ result = __ieee754_log10l (d) - scale * M_LOG10_2l;
 109         }
 110
 111       __imag__ result = M_LOG10El * __ieee754_atan2l (__imag__ x, __real__ x);
 112     }
 113   else
 114     {
 115       __imag__ result = __nanl ("");
 116       if (rcls == FP_INFINITE || icls == FP_INFINITE)
 117         /* Real or imaginary part is infinite.  */
 118         __real__ result = HUGE_VALL;
 119       else
 120         __real__ result = __nanl ("");
 121     }
 122
 123   return result;
 124 }
 125 weak_alias (__clog10l, clog10l)