1 /* Return arc hyperbole cosine for double value.
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.
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.
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.
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/>. */
22 #include <math_private.h>
26 __cacosh (__complex__
double x
)
28 __complex__
double res
;
29 int rcls
= fpclassify (__real__ x
);
30 int icls
= fpclassify (__imag__ x
);
32 if (rcls
<= FP_INFINITE
|| icls
<= FP_INFINITE
)
34 if (icls
== FP_INFINITE
)
36 __real__ res
= HUGE_VAL
;
39 __imag__ res
= __nan ("");
41 __imag__ res
= __copysign ((rcls
== FP_INFINITE
43 ? M_PI
- M_PI_4
: M_PI_4
)
44 : M_PI_2
), __imag__ x
);
46 else if (rcls
== FP_INFINITE
)
48 __real__ res
= HUGE_VAL
;
51 __imag__ res
= __copysign (signbit (__real__ x
) ? M_PI
: 0.0,
54 __imag__ res
= __nan ("");
58 __real__ res
= __nan ("");
59 __imag__ res
= __nan ("");
62 else if (rcls
== FP_ZERO
&& icls
== FP_ZERO
)
65 __imag__ res
= __copysign (M_PI_2
, __imag__ x
);
67 /* The factor 16 is just a guess. */
68 else if (16.0 * fabs (__imag__ x
) < fabs (__real__ x
))
70 /* Kahan's formula which avoid cancellation through subtraction in
72 res
= 2.0 * __clog (__csqrt ((x
+ 1.0) / 2.0) + __csqrt ((x
- 1.0) / 2.0));
73 if (signbit (__real__ res
))
80 __real__ y
= (__real__ x
- __imag__ x
) * (__real__ x
+ __imag__ x
) - 1.0;
81 __imag__ y
= 2.0 * __real__ x
* __imag__ x
;
85 if (signbit (__real__ x
))
88 __real__ y
+= __real__ x
;
89 __imag__ y
+= __imag__ x
;
96 weak_alias (__cacosh
, cacosh
)
98 strong_alias (__cacosh
, __cacoshl
)
99 weak_alias (__cacosh
, cacoshl
)