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glibc  2.9
e_gamma_r.c
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00001 /* Implementation of gamma function according to ISO C.
00002    Copyright (C) 1997, 1999, 2001, 2004 Free Software Foundation, Inc.
00003    This file is part of the GNU C Library.
00004    Contributed by Ulrich Drepper <drepper@cygnus.com>, 1997.
00005 
00006    The GNU C Library is free software; you can redistribute it and/or
00007    modify it under the terms of the GNU Lesser General Public
00008    License as published by the Free Software Foundation; either
00009    version 2.1 of the License, or (at your option) any later version.
00010 
00011    The GNU C Library is distributed in the hope that it will be useful,
00012    but WITHOUT ANY WARRANTY; without even the implied warranty of
00013    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
00014    Lesser General Public License for more details.
00015 
00016    You should have received a copy of the GNU Lesser General Public
00017    License along with the GNU C Library; if not, write to the Free
00018    Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA
00019    02111-1307 USA.  */
00020 
00021 #include <math.h>
00022 #include <math_private.h>
00023 
00024 
00025 double
00026 __ieee754_gamma_r (double x, int *signgamp)
00027 {
00028   /* We don't have a real gamma implementation now.  We'll use lgamma
00029      and the exp function.  But due to the required boundary
00030      conditions we must check some values separately.  */
00031   int32_t hx;
00032   u_int32_t lx;
00033 
00034   EXTRACT_WORDS (hx, lx, x);
00035 
00036   if (((hx & 0x7fffffff) | lx) == 0)
00037     {
00038       /* Return value for x == 0 is Inf with divide by zero exception.  */
00039       *signgamp = 0;
00040       return 1.0 / x;
00041     }
00042   if (hx < 0 && (u_int32_t) hx < 0xfff00000 && __rint (x) == x)
00043     {
00044       /* Return value for integer x < 0 is NaN with invalid exception.  */
00045       *signgamp = 0;
00046       return (x - x) / (x - x);
00047     }
00048   if ((unsigned int) hx == 0xfff00000 && lx==0)
00049     {
00050       /* x == -Inf.  According to ISO this is NaN.  */
00051       *signgamp = 0;
00052       return x - x;
00053     }
00054 
00055   /* XXX FIXME.  */
00056   return __ieee754_exp (__ieee754_lgamma_r (x, signgamp));
00057 }