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glibc  2.9
e_gammal_r.c
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00001 /* Implementation of gamma function according to ISO C.
00002    Copyright (C) 1997, 1999, 2002, 2004 Free Software Foundation, Inc.
00003    This file is part of the GNU C Library.
00004    Contributed by Ulrich Drepper <drepper@cygnus.com>, 1997 and
00005                 Jakub Jelinek <jj@ultra.linux.cz, 1999.
00006 
00007    The GNU C Library is free software; you can redistribute it and/or
00008    modify it under the terms of the GNU Lesser General Public
00009    License as published by the Free Software Foundation; either
00010    version 2.1 of the License, or (at your option) any later version.
00011 
00012    The GNU C Library is distributed in the hope that it will be useful,
00013    but WITHOUT ANY WARRANTY; without even the implied warranty of
00014    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
00015    Lesser General Public License for more details.
00016 
00017    You should have received a copy of the GNU Lesser General Public
00018    License along with the GNU C Library; if not, write to the Free
00019    Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA
00020    02111-1307 USA.  */
00021 
00022 #include <math.h>
00023 #include <math_private.h>
00024 
00025 
00026 long double
00027 __ieee754_gammal_r (long double x, int *signgamp)
00028 {
00029   /* We don't have a real gamma implementation now.  We'll use lgamma
00030      and the exp function.  But due to the required boundary
00031      conditions we must check some values separately.  */
00032   int64_t hx;
00033   u_int64_t lx;
00034 
00035   GET_LDOUBLE_WORDS64 (hx, lx, x);
00036 
00037   if (((hx & 0x7fffffffffffffffLL) | lx) == 0)
00038     {
00039       /* Return value for x == 0 is Inf with divide by zero exception.  */
00040       *signgamp = 0;
00041       return 1.0 / x;
00042     }
00043   if (hx < 0 && (u_int64_t) hx < 0xffff000000000000ULL && __rintl (x) == x)
00044     {
00045       /* Return value for integer x < 0 is NaN with invalid exception.  */
00046       *signgamp = 0;
00047       return (x - x) / (x - x);
00048     }
00049   if (hx == 0xffff000000000000ULL && lx == 0)
00050     {
00051       /* x == -Inf.  According to ISO this is NaN.  */
00052       *signgamp = 0;
00053       return x - x;
00054     }
00055 
00056   /* XXX FIXME.  */
00057   return __ieee754_expl (__ieee754_lgammal_r (x, signgamp));
00058 }