math/s_clog10f.c

   1 /* Compute complex base 10 logarithm.
   2    Copyright (C) 1997-2013 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_2f 0.3010299956639811952137388947244930267682f
  27
  28 __complex__ float
  29 __clog10f (__complex__ float x)
  30 {
  31   __complex__ float 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 = __copysignf (__imag__ result, __imag__ x);
  40       /* Yes, the following line raises an exception.  */
  41       __real__ result = -1.0 / fabsf (__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       float absx = fabsf (__real__ x), absy = fabsf (__imag__ x);
  47       int scale = 0;
  48
  49       if (absx < absy)
  50         {
  51           float t = absx;
  52           absx = absy;
  53           absy = t;
  54         }
  55
  56       if (absx > FLT_MAX / 2.0f)
  57         {
  58           scale = -1;
  59           absx = __scalbnf (absx, scale);
  60           absy = (absy >= FLT_MIN * 2.0f ? __scalbnf (absy, scale) : 0.0f);
  61         }
  62       else if (absx < FLT_MIN && absy < FLT_MIN)
  63         {
  64           scale = FLT_MANT_DIG;
  65           absx = __scalbnf (absx, scale);
  66           absy = __scalbnf (absy, scale);
  67         }
  68
  69       if (absx == 1.0f && scale == 0)
  70         {
  71           float absy2 = absy * absy;
  72           if (absy2 <= FLT_MIN * 2.0f * (float) M_LN10)
  73             {
  74 #if __FLT_EVAL_METHOD__ == 0
  75               __real__ result
  76                 = (absy2 / 2.0f - absy2 * absy2 / 4.0f) * (float) M_LOG10E;
  77 #else
  78               volatile float force_underflow = absy2 * absy2 / 4.0f;
  79               __real__ result
  80                 = (absy2 / 2.0f - force_underflow) * (float) M_LOG10E;
  81 #endif
  82             }
  83           else
  84             __real__ result = __log1pf (absy2) * ((float) M_LOG10E / 2.0f);
  85         }
  86       else if (absx > 1.0f && absx < 2.0f && absy < 1.0f && scale == 0)
  87         {
  88           float d2m1 = (absx - 1.0f) * (absx + 1.0f);
  89           if (absy >= FLT_EPSILON)
  90             d2m1 += absy * absy;
  91           __real__ result = __log1pf (d2m1) * ((float) M_LOG10E / 2.0f);
  92         }
  93       else if (absx < 1.0f
  94                && absx >= 0.75f
  95                && absy < FLT_EPSILON / 2.0f
  96                && scale == 0)
  97         {
  98           float d2m1 = (absx - 1.0f) * (absx + 1.0f);
  99           __real__ result = __log1pf (d2m1) * ((float) M_LOG10E / 2.0f);
 100         }
 101       else if (absx < 1.0f && (absx >= 0.75f || absy >= 0.5f) && scale == 0)
 102         {
 103           float d2m1 = __x2y2m1f (absx, absy);
 104           __real__ result = __log1pf (d2m1) * ((float) M_LOG10E / 2.0f);
 105         }
 106       else
 107         {
 108           float d = __ieee754_hypotf (absx, absy);
 109           __real__ result = __ieee754_log10f (d) - scale * M_LOG10_2f;
 110         }
 111
 112       __imag__ result = M_LOG10E * __ieee754_atan2f (__imag__ x, __real__ x);
 113     }
 114   else
 115     {
 116       __imag__ result = __nanf ("");
 117       if (rcls == FP_INFINITE || icls == FP_INFINITE)
 118         /* Real or imaginary part is infinite.  */
 119         __real__ result = HUGE_VALF;
 120       else
 121         __real__ result = __nanf ("");
 122     }
 123
 124   return result;
 125 }
 126 #ifndef __clog10f
 127 weak_alias (__clog10f, clog10f)
 128 #endif