sysdeps/ieee754/dbl-64/e_gamma_r.c

   1 /* Implementation of gamma function according to ISO C.
   2    Copyright (C) 1997, 1999, 2001, 2004 Free Software Foundation, Inc.
   3    This file is part of the GNU C Library.
   4    Contributed by Ulrich Drepper <drepper@cygnus.com>, 1997.
   5
   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.
  10
  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.
  15
  16    You should have received a copy of the GNU Lesser General Public
  17    License along with the GNU C Library; if not, write to the Free
  18    Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA
  19    02111-1307 USA.  */
  20
  21 #include <math.h>
  22 #include <math_private.h>
  23
  24
  25 double
  26 __ieee754_gamma_r (double x, int *signgamp)
  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   int32_t hx;
  32   u_int32_t lx;
  33
  34   EXTRACT_WORDS (hx, lx, x);
  35
  36   if (((hx & 0x7fffffff) | lx) == 0)
  37     {
  38       /* Return value for x == 0 is Inf with divide by zero exception.  */
  39       *signgamp = 0;
  40       return 1.0 / x;
  41     }
  42   if (hx < 0 && (u_int32_t) hx < 0xfff00000 && __rint (x) == x)
  43     {
  44       /* Return value for integer x < 0 is NaN with invalid exception.  */
  45       *signgamp = 0;
  46       return (x - x) / (x - x);
  47     }
  48   if ((unsigned int) hx == 0xfff00000 && lx==0)
  49     {
  50       /* x == -Inf.  According to ISO this is NaN.  */
  51       *signgamp = 0;
  52       return x - x;
  53     }
  54
  55   /* XXX FIXME.  */
  56   return __ieee754_exp (__ieee754_lgamma_r (x, signgamp));
  57 }