1/* Implementation of gamma function according to ISO C.
2 Copyright (C) 1997, 1999, 2002, 2004 Free Software Foundation, Inc.
3 This file is part of the GNU C Library.
4 Contributed by Ulrich Drepper <drepper@cygnus.com>, 1997 and
5 Jakub Jelinek <jj@ultra.linux.cz, 1999.
6
7 The GNU C Library is free software; you can redistribute it and/or
8 modify it under the terms of the GNU Lesser General Public
9 License as published by the Free Software Foundation; either
10 version 2.1 of the License, or (at your option) any later version.
11
12 The GNU C Library is distributed in the hope that it will be useful,
13 but WITHOUT ANY WARRANTY; without even the implied warranty of
14 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
15 Lesser General Public License for more details.
16
17 You should have received a copy of the GNU Lesser General Public
18 License along with the GNU C Library; if not, write to the Free
19 Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA
20 02111-1307 USA. */
21
22#include "quadmath-imp.h"
23
24
25__float128
26tgammaq (__float128 x)
27{
28 /* We don't have a real gamma implementation now. We'll use lgamma
29 and the exp function. But due to the required boundary
30 conditions we must check some values separately. */
31 int64_t hx;
32 uint64_t lx;
33 __float128 res;
34 int sign;
35
36 GET_FLT128_WORDS64 (hx, lx, x);
37
38 if (((hx & 0x7fffffffffffffffLL) | lx) == 0)
39 /* Return value for x == 0 is Inf with divide by zero exception. */
40 return 1.0 / x;
41
42 if (hx < 0 && (uint64_t) hx < 0xffff000000000000ULL && rintq (x) == x)
43 /* Return value for integer x < 0 is NaN with invalid exception. */
44 return (x - x) / (x - x);
45
46 if (hx == 0xffff000000000000ULL && lx == 0)
47 /* x == -Inf. According to ISO this is NaN. */
48 return x - x;
49
50 /* XXX FIXME. */
51 res = expq (lgammaq (x));
52 return signbitq (x) ? -res : res;
53}
54