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glibc  2.9
e_gammaf_r.c
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00001 /* Implementation of gamma function according to ISO C.
00002    Copyright (C) 1997, 1999, 2001, 2004 Free Software Foundation, Inc.
00003    This file is part of the GNU C Library.
00004    Contributed by Ulrich Drepper <drepper@cygnus.com>, 1997.
00005 
00006    The GNU C Library is free software; you can redistribute it and/or
00007    modify it under the terms of the GNU Lesser General Public
00008    License as published by the Free Software Foundation; either
00009    version 2.1 of the License, or (at your option) any later version.
00010 
00011    The GNU C Library is distributed in the hope that it will be useful,
00012    but WITHOUT ANY WARRANTY; without even the implied warranty of
00013    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
00014    Lesser General Public License for more details.
00015 
00016    You should have received a copy of the GNU Lesser General Public
00017    License along with the GNU C Library; if not, write to the Free
00018    Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA
00019    02111-1307 USA.  */
00020 
00021 #include <math.h>
00022 #include <math_private.h>
00023 
00024 
00025 float
00026 __ieee754_gammaf_r (float x, int *signgamp)
00027 {
00028   /* We don't have a real gamma implementation now.  We'll use lgamma
00029      and the exp function.  But due to the required boundary
00030      conditions we must check some values separately.  */
00031   int32_t hx;
00032 
00033   GET_FLOAT_WORD (hx, x);
00034 
00035   if ((hx & 0x7fffffff) == 0)
00036     {
00037       /* Return value for x == 0 is Inf with divide by zero exception.  */
00038       *signgamp = 0;
00039       return 1.0 / x;
00040     }
00041   if (hx < 0 && (u_int32_t) hx < 0xff800000 && __rintf (x) == x)
00042     {
00043       /* Return value for integer x < 0 is NaN with invalid exception.  */
00044       *signgamp = 0;
00045       return (x - x) / (x - x);
00046     }
00047   if (hx == 0xff800000)
00048     {
00049       /* x == -Inf.  According to ISO this is NaN.  */
00050       *signgamp = 0;
00051       return x - x;
00052     }
00053 
00054   /* XXX FIXME.  */
00055   return __ieee754_expf (__ieee754_lgammaf_r (x, signgamp));
00056 }