libquadmath/math/tgammaq.c

   1 /* Implementation of gamma function according to ISO C.
   2    Copyright (C) 1997, 1999, 2002, 2004 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 "quadmath-imp.h"
  23
  24
  25 __float128
  26 tgammaq (__float128 x)
  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   int64_t hx;
  32   uint64_t lx;
  33   __float128 res;
  34   int sign;
  35
  36   GET_FLT128_WORDS64 (hx, lx, x);
  37
  38   if (((hx & 0x7fffffffffffffffLL) | lx) == 0)
  39     /* Return value for x == 0 is Inf with divide by zero exception.  */
  40     return 1.0 / x;
  41
  42   if (hx < 0 && (uint64_t) hx < 0xffff000000000000ULL && rintq (x) == x)
  43     /* Return value for integer x < 0 is NaN with invalid exception.  */
  44     return (x - x) / (x - x);
  45
  46   if (hx == 0xffff000000000000ULL && lx == 0)
  47     /* x == -Inf.  According to ISO this is NaN.  */
  48     return x - x;
  49
  50   /* XXX FIXME.  */
  51   res = expq (lgammaq (x));
  52   return signbitq (x) ? -res : res;
  53 }