math/s_ctanh.c

   1 /* Complex hyperbole tangent for double.
   2    Copyright (C) 1997-2016 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 <fenv.h>
  22 #include <math.h>
  23 #include <math_private.h>
  24 #include <float.h>
  25
  26 __complex__ double
  27 __ctanh (__complex__ double x)
  28 {
  29   __complex__ double res;
  30
  31   if (__glibc_unlikely (!isfinite (__real__ x) || !isfinite (__imag__ x)))
  32     {
  33       if (isinf (__real__ x))
  34         {
  35           __real__ res = __copysign (1.0, __real__ x);
  36           if (isfinite (__imag__ x) && fabs (__imag__ x) > 1.0)
  37             {
  38               double sinix, cosix;
  39               __sincos (__imag__ x, &sinix, &cosix);
  40               __imag__ res = __copysign (0.0, sinix * cosix);
  41             }
  42           else
  43             __imag__ res = __copysign (0.0, __imag__ x);
  44         }
  45       else if (__imag__ x == 0.0)
  46         {
  47           res = x;
  48         }
  49       else
  50         {
  51           __real__ res = __nan ("");
  52           __imag__ res = __nan ("");
  53
  54           if (isinf (__imag__ x))
  55             feraiseexcept (FE_INVALID);
  56         }
  57     }
  58   else
  59     {
  60       double sinix, cosix;
  61       double den;
  62       const int t = (int) ((DBL_MAX_EXP - 1) * M_LN2 / 2);
  63
  64       /* tanh(x+iy) = (sinh(2x) + i*sin(2y))/(cosh(2x) + cos(2y))
  65          = (sinh(x)*cosh(x) + i*sin(y)*cos(y))/(sinh(x)^2 + cos(y)^2).  */
  66
  67       if (__glibc_likely (fabs (__imag__ x) > DBL_MIN))
  68         {
  69           __sincos (__imag__ x, &sinix, &cosix);
  70         }
  71       else
  72         {
  73           sinix = __imag__ x;
  74           cosix = 1.0;
  75         }
  76
  77       if (fabs (__real__ x) > t)
  78         {
  79           /* Avoid intermediate overflow when the imaginary part of
  80              the result may be subnormal.  Ignoring negligible terms,
  81              the real part is +/- 1, the imaginary part is
  82              sin(y)*cos(y)/sinh(x)^2 = 4*sin(y)*cos(y)/exp(2x).  */
  83           double exp_2t = __ieee754_exp (2 * t);
  84
  85           __real__ res = __copysign (1.0, __real__ x);
  86           __imag__ res = 4 * sinix * cosix;
  87           __real__ x = fabs (__real__ x);
  88           __real__ x -= t;
  89           __imag__ res /= exp_2t;
  90           if (__real__ x > t)
  91             {
  92               /* Underflow (original real part of x has absolute value
  93                  > 2t).  */
  94               __imag__ res /= exp_2t;
  95             }
  96           else
  97             __imag__ res /= __ieee754_exp (2 * __real__ x);
  98         }
  99       else
 100         {
 101           double sinhrx, coshrx;
 102           if (fabs (__real__ x) > DBL_MIN)
 103             {
 104               sinhrx = __ieee754_sinh (__real__ x);
 105               coshrx = __ieee754_cosh (__real__ x);
 106             }
 107           else
 108             {
 109               sinhrx = __real__ x;
 110               coshrx = 1.0;
 111             }
 112
 113           if (fabs (sinhrx) > fabs (cosix) * DBL_EPSILON)
 114             den = sinhrx * sinhrx + cosix * cosix;
 115           else
 116             den = cosix * cosix;
 117           __real__ res = sinhrx * coshrx / den;
 118           __imag__ res = sinix * cosix / den;
 119         }
 120       math_check_force_underflow_complex (res);
 121     }
 122
 123   return res;
 124 }
 125 weak_alias (__ctanh, ctanh)
 126 #ifdef NO_LONG_DOUBLE
 127 strong_alias (__ctanh, __ctanhl)
 128 weak_alias (__ctanh, ctanhl)
 129 #endif