sysdeps/ieee754/dbl-64/e_gamma_r.c

/* Implementation of gamma function according to ISO C.
   Copyright (C) 1997, 1999, 2001, 2004 Free Software Foundation, Inc.
   This file is part of the GNU C Library.
   Contributed by Ulrich Drepper <drepper@cygnus.com>, 1997.

   The GNU C Library is free software; you can redistribute it and/or
   modify it under the terms of the GNU Lesser General Public
   License as published by the Free Software Foundation; either
   version 2.1 of the License, or (at your option) any later version.

   The GNU C Library is distributed in the hope that it will be useful,
   but WITHOUT ANY WARRANTY; without even the implied warranty of
   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
   Lesser General Public License for more details.

   You should have received a copy of the GNU Lesser General Public
   License along with the GNU C Library; if not, write to the Free
   Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA
   02111-1307 USA.  */

#include <math.h>
#include <math_private.h>


double
__ieee754_gamma_r (double x, int *signgamp)
{
  /* We don't have a real gamma implementation now.  We'll use lgamma
     and the exp function.  But due to the required boundary
     conditions we must check some values separately.  */
  int32_t hx;
  u_int32_t lx;

  EXTRACT_WORDS (hx, lx, x);

  if (((hx & 0x7fffffff) | lx) == 0)
    {
      /* Return value for x == 0 is Inf with divide by zero exception.  */
      *signgamp = 0;
      return 1.0 / x;
    }
  if (hx < 0 && (u_int32_t) hx < 0xfff00000 && __rint (x) == x)
    {
      /* Return value for integer x < 0 is NaN with invalid exception.  */
      *signgamp = 0;
      return (x - x) / (x - x);
    }
  if ((unsigned int) hx == 0xfff00000 && lx==0)
    {
      /* x == -Inf.  According to ISO this is NaN.  */
      *signgamp = 0;
      return x - x;
    }

  /* XXX FIXME.  */
  return __ieee754_exp (__ieee754_lgamma_r (x, signgamp));
}