math/s_clog10f.c

   1 /* Compute complex base 10 logarithm.
   2    Copyright (C) 1997-2015 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 /* pi * log10 (e).  */
  29 #define M_PI_LOG10Ef 1.364376353841841347485783625431355770210f
  30
  31 __complex__ float
  32 __clog10f (__complex__ float x)
  33 {
  34   __complex__ float result;
  35   int rcls = fpclassify (__real__ x);
  36   int icls = fpclassify (__imag__ x);
  37
  38   if (__glibc_unlikely (rcls == FP_ZERO && icls == FP_ZERO))
  39     {
  40       /* Real and imaginary part are 0.0.  */
  41       __imag__ result = signbit (__real__ x) ? M_PI_LOG10Ef : 0.0;
  42       __imag__ result = __copysignf (__imag__ result, __imag__ x);
  43       /* Yes, the following line raises an exception.  */
  44       __real__ result = -1.0 / fabsf (__real__ x);
  45     }
  46   else if (__glibc_likely (rcls != FP_NAN && icls != FP_NAN))
  47     {
  48       /* Neither real nor imaginary part is NaN.  */
  49       float absx = fabsf (__real__ x), absy = fabsf (__imag__ x);
  50       int scale = 0;
  51
  52       if (absx < absy)
  53         {
  54           float t = absx;
  55           absx = absy;
  56           absy = t;
  57         }
  58
  59       if (absx > FLT_MAX / 2.0f)
  60         {
  61           scale = -1;
  62           absx = __scalbnf (absx, scale);
  63           absy = (absy >= FLT_MIN * 2.0f ? __scalbnf (absy, scale) : 0.0f);
  64         }
  65       else if (absx < FLT_MIN && absy < FLT_MIN)
  66         {
  67           scale = FLT_MANT_DIG;
  68           absx = __scalbnf (absx, scale);
  69           absy = __scalbnf (absy, scale);
  70         }
  71
  72       if (absx == 1.0f && scale == 0)
  73         {
  74           float absy2 = absy * absy;
  75           if (absy2 <= FLT_MIN * 2.0f * (float) M_LN10)
  76             {
  77               float force_underflow = absy2 * absy2;
  78               __real__ result = absy2 * ((float) M_LOG10E / 2.0f);
  79               math_force_eval (force_underflow);
  80             }
  81           else
  82             __real__ result = __log1pf (absy2) * ((float) M_LOG10E / 2.0f);
  83         }
  84       else if (absx > 1.0f && absx < 2.0f && absy < 1.0f && scale == 0)
  85         {
  86           float d2m1 = (absx - 1.0f) * (absx + 1.0f);
  87           if (absy >= FLT_EPSILON)
  88             d2m1 += absy * absy;
  89           __real__ result = __log1pf (d2m1) * ((float) M_LOG10E / 2.0f);
  90         }
  91       else if (absx < 1.0f
  92                && absx >= 0.75f
  93                && absy < FLT_EPSILON / 2.0f
  94                && scale == 0)
  95         {
  96           float d2m1 = (absx - 1.0f) * (absx + 1.0f);
  97           __real__ result = __log1pf (d2m1) * ((float) M_LOG10E / 2.0f);
  98         }
  99       else if (absx < 1.0f && (absx >= 0.75f || absy >= 0.5f) && scale == 0)
 100         {
 101           float d2m1 = __x2y2m1f (absx, absy);
 102           __real__ result = __log1pf (d2m1) * ((float) M_LOG10E / 2.0f);
 103         }
 104       else
 105         {
 106           float d = __ieee754_hypotf (absx, absy);
 107           __real__ result = __ieee754_log10f (d) - scale * M_LOG10_2f;
 108         }
 109
 110       __imag__ result = M_LOG10E * __ieee754_atan2f (__imag__ x, __real__ x);
 111     }
 112   else
 113     {
 114       __imag__ result = __nanf ("");
 115       if (rcls == FP_INFINITE || icls == FP_INFINITE)
 116         /* Real or imaginary part is infinite.  */
 117         __real__ result = HUGE_VALF;
 118       else
 119         __real__ result = __nanf ("");
 120     }
 121
 122   return result;
 123 }
 124 #ifndef __clog10f
 125 weak_alias (__clog10f, clog10f)
 126 #endif