1 /* Implementation of gamma function according to ISO C.
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.
6 The GNU C Library is free software; you can redistribute it and/or
7 modify it under the terms of the GNU Library General Public License as
8 published by the Free Software Foundation; either version 2 of the
9 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 Library General Public License for more details.
16 You should have received a copy of the GNU Library General Public
17 License along with the GNU C Library; see the file COPYING.LIB. If not,
18 write to the Free Software Foundation, Inc., 59 Temple Place - Suite 330,
19 Boston, MA 02111-1307, USA. */
22 #include <math_private.h>
26 __ieee754_gamma_r (double x
, int *signgamp
)
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. */
34 EXTRACT_WORDS (hx
, lx
, x
);
36 if (((hx
& 0x7fffffff) | lx
) == 0)
37 /* Return value for x == 0 is NaN with invalid exception. */
39 if (hx
< 0 && (u_int32_t
) hx
< 0xfff00000 && __rint (x
) == x
)
41 /* Return value for integer x < 0 is NaN with invalid exception. */
42 return (x
- x
) / (x
- x
);
46 return __ieee754_exp (__ieee754_lgamma_r (x
, signgamp
));