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52 lines
1.8 KiB
C
52 lines
1.8 KiB
C
/* Implementation of gamma function according to ISO C.
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Copyright (C) 1997, 1999 Free Software Foundation, Inc.
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This file is part of the GNU C Library.
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Contributed by Ulrich Drepper <drepper@cygnus.com>, 1997.
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The GNU C Library is free software; you can redistribute it and/or
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modify it under the terms of the GNU Library General Public License as
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published by the Free Software Foundation; either version 2 of the
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License, or (at your option) any later version.
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The GNU C Library is distributed in the hope that it will be useful,
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but WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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Library General Public License for more details.
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You should have received a copy of the GNU Library General Public
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License along with the GNU C Library; see the file COPYING.LIB. If not,
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write to the Free Software Foundation, Inc., 59 Temple Place - Suite 330,
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Boston, MA 02111-1307, USA. */
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#include <math.h>
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#include <math_private.h>
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double
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__ieee754_gamma_r (double x, int *signgamp)
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{
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/* We don't have a real gamma implementation now. We'll use lgamma
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and the exp function. But due to the required boundary
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conditions we must check some values separately. */
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int32_t hx;
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u_int32_t lx;
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EXTRACT_WORDS (hx, lx, x);
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if (((hx & 0x7fffffff) | lx) == 0)
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{
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/* Return value for x == 0 is NaN with invalid exception. */
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*signgamp = 0;
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return x / x;
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}
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if (hx < 0 && (u_int32_t) hx < 0xfff00000 && __rint (x) == x)
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{
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/* Return value for integer x < 0 is NaN with invalid exception. */
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*signgamp = 0;
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return (x - x) / (x - x);
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}
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/* XXX FIXME. */
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return __ieee754_exp (__ieee754_lgamma_r (x, signgamp));
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}
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