glibc/sysdeps/libm-ieee754/e_gamma_r.c

/* Implementation of gamma function according to ISO C.
   Copyright (C) 1997 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 Library General Public License as
   published by the Free Software Foundation; either version 2 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
   Library General Public License for more details.

   You should have received a copy of the GNU Library General Public
   License along with the GNU C Library; see the file COPYING.LIB.  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 NaN with invalid exception.  */
    return x / x;
  if (hx < 0 && (u_int32_t) hx < 0xfff00000 && __rint (x) == x)
    {
      /* Return value for integer x < 0 is NaN with invalid exception.  */
      return (x - x) / (x - x);
    }

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