sysdeps/ieee754/ldbl-96/e_gammal_r.c

   1 /* Implementation of gamma function according to ISO C.
   2    Copyright (C) 1997,1999,2001,2003,2004,2011 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, see
  18    <http://www.gnu.org/licenses/>.  */
  19
  20 #include <math.h>
  21 #include <math_private.h>
  22
  23
  24 long double
  25 __ieee754_gammal_r (long double x, int *signgamp)
  26 {
  27   /* We don't have a real gamma implementation now.  We'll use lgamma
  28      and the exp function.  But due to the required boundary
  29      conditions we must check some values separately.  */
  30   u_int32_t es, hx, lx;
  31
  32   GET_LDOUBLE_WORDS (es, hx, lx, x);
  33
  34   if (__builtin_expect (((es & 0x7fff) | hx | lx) == 0, 0))
  35     {
  36       /* Return value for x == 0 is Inf with divide by zero exception.  */
  37       *signgamp = 0;
  38       return 1.0 / x;
  39     }
  40   if (__builtin_expect (es == 0xffffffff && ((hx & 0x7fffffff) | lx) == 0, 0))
  41     {
  42       /* x == -Inf.  According to ISO this is NaN.  */
  43       *signgamp = 0;
  44       return x - x;
  45     }
  46   if (__builtin_expect ((es & 0x7fff) == 0x7fff, 0)
  47       && ((hx & 0x7fffffff) | lx) != 0)
  48     {
  49       /* NaN, return it.  */
  50       *signgamp = 0;
  51       return x;
  52     }
  53   if (__builtin_expect ((es & 0x8000) != 0, 0)
  54       && x < 0xffffffff && __rintl (x) == x)
  55     {
  56       /* Return value for integer x < 0 is NaN with invalid exception.  */
  57       *signgamp = 0;
  58       return (x - x) / (x - x);
  59     }
  60
  61   /* XXX FIXME.  */
  62   return __ieee754_expl (__ieee754_lgammal_r (x, signgamp));
  63 }
  64 strong_alias (__ieee754_gammal_r, __gammal_r_finite)