1/* Return arc tangent of complex double value.
2   Copyright (C) 1997 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, write to the Free
18   Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA
19   02111-1307 USA.  */
20
21#include <complex.h>
22#include <math.h>
23
24#include "math_private.h"
25
26
27__complex__ double
28__catan (__complex__ double x)
29{
30  __complex__ double res;
31  int rcls = fpclassify (__real__ x);
32  int icls = fpclassify (__imag__ x);
33
34  if (rcls <= FP_INFINITE || icls <= FP_INFINITE)
35    {
36      if (rcls == FP_INFINITE)
37	{
38	  __real__ res = copysign (M_PI_2, __real__ x);
39	  __imag__ res = copysign (0.0, __imag__ x);
40	}
41      else if (icls == FP_INFINITE)
42	{
43	  if (rcls >= FP_ZERO)
44	    __real__ res = copysign (M_PI_2, __real__ x);
45	  else
46	    __real__ res = nan ("");
47	  __imag__ res = copysign (0.0, __imag__ x);
48	}
49      else if (icls == FP_ZERO || icls == FP_INFINITE)
50	{
51	  __real__ res = nan ("");
52	  __imag__ res = copysign (0.0, __imag__ x);
53	}
54      else
55	{
56	  __real__ res = nan ("");
57	  __imag__ res = nan ("");
58	}
59    }
60  else if (rcls == FP_ZERO && icls == FP_ZERO)
61    {
62      res = x;
63    }
64  else
65    {
66      double r2, num, den;
67
68      r2 = __real__ x * __real__ x;
69
70      den = 1 - r2 - __imag__ x * __imag__ x;
71
72      __real__ res = 0.5 * atan2 (2.0 * __real__ x, den);
73
74      num = __imag__ x + 1.0;
75      num = r2 + num * num;
76
77      den = __imag__ x - 1.0;
78      den = r2 + den * den;
79
80      __imag__ res = 0.25 * log (num / den);
81    }
82
83  return res;
84}
85weak_alias (__catan, catan)
86#ifdef NO_LONG_DOUBLE
87strong_alias (__catan, __catanl)
88weak_alias (__catan, catanl)
89#endif
90