sysdeps/libm-ieee754/e_gammal_r.c

   1 /* Implementation of gamma function according to ISO C.
   2    Copyright (C) 1997 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 Library General Public License as
   8    published by the Free Software Foundation; either version 2 of the
   9    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    Library General Public License for more details.
  15
  16    You should have received a copy of the GNU Library General Public
  17    License along with the GNU C Library; see the file COPYING.LIB.  If not,
  18    write to the Free Software Foundation, Inc., 59 Temple Place - Suite 330,
  19    Boston, MA 02111-1307, USA.  */
  20
  21 #include <math.h>
  22 #include <math_private.h>
  23
  24
  25 long double
  26 __ieee754_gammal_r (long 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   u_int32_t es, hx, lx;
  32
  33   GET_LDOUBLE_WORDS (es, hx, lx, x);
  34
  35   if (((es & 0x7fff) | hx | lx) == 0)
  36     /* Return value for x == 0 is NaN with invalid exception.  */
  37     return x / x;
  38   if ((hx & 0x8000) != 0 && (hx & 0x7fff) != 0x7fff && __rintl (x) == x)
  39     {
  40       /* Return value for integer x < 0 is NaN with invalid exception.  */
  41       return (x - x) / (x - x);
  42     }
  43
  44   /* XXX FIXME.  */
  45   return __ieee754_expl (__ieee754_lgammal_r (x, signgamp));
  46 }