1 /* Return arc hyperbole cosine for double value.
2 Copyright (C) 1997-2012 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)