sysdeps/ieee754/ldbl-128ibm/e_gammal_r.c

   1 /* Implementation of gamma function according to ISO C.
   2    Copyright (C) 1997,1999,2002,2004,2006 Free Software Foundation, Inc.
   3    This file is part of the GNU C Library.
   4    Contributed by Ulrich Drepper <drepper@cygnus.com>, 1997 and
   5                   Jakub Jelinek <jj@ultra.linux.cz, 1999.
   6
   7    The GNU C Library is free software; you can redistribute it and/or
   8    modify it under the terms of the GNU Lesser General Public
   9    License as published by the Free Software Foundation; either
  10    version 2.1 of the License, or (at your option) any later version.
  11
  12    The GNU C Library is distributed in the hope that it will be useful,
  13    but WITHOUT ANY WARRANTY; without even the implied warranty of
  14    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  15    Lesser General Public License for more details.
  16
  17    You should have received a copy of the GNU Lesser General Public
  18    License along with the GNU C Library; if not, write to the Free
  19    Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA
  20    02111-1307 USA.  */
  21
  22 #include <math.h>
  23 #include <math_private.h>
  24
  25
  26 long double
  27 __ieee754_gammal_r (long double x, int *signgamp)
  28 {
  29   /* We don't have a real gamma implementation now.  We'll use lgamma
  30      and the exp function.  But due to the required boundary
  31      conditions we must check some values separately.  */
  32   int64_t hx;
  33   u_int64_t lx;
  34
  35   GET_LDOUBLE_WORDS64 (hx, lx, x);
  36
  37   if (((hx | lx) & 0x7fffffffffffffffLL) == 0)
  38     {
  39       /* Return value for x == 0 is Inf with divide by zero exception.  */
  40       *signgamp = 0;
  41       return 1.0 / x;
  42     }
  43   if (hx < 0 && (u_int64_t) hx < 0xfff0000000000000ULL && __rintl (x) == x)
  44     {
  45       /* Return value for integer x < 0 is NaN with invalid exception.  */
  46       *signgamp = 0;
  47       return (x - x) / (x - x);
  48     }
  49   if (hx == 0xfff0000000000000ULL)
  50     {
  51       /* x == -Inf.  According to ISO this is NaN.  */
  52       *signgamp = 0;
  53       return x - x;
  54     }
  55
  56   /* XXX FIXME.  */
  57   return __ieee754_expl (__ieee754_lgammal_r (x, signgamp));
  58 }