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/* Compute x * y + z as ternary operation.
Copyright (C) 2010-2012 Free Software Foundation, Inc.
This file is part of the GNU C Library.
Contributed by Jakub Jelinek <jakub@redhat.com>, 2010.
The GNU C Library is free software; you can redistribute it and/or
modify it under the terms of the GNU Lesser General Public
License as published by the Free Software Foundation; either
version 2.1 of the License, or (at your option) any later version.
The GNU C Library is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
Lesser General Public License for more details.
You should have received a copy of the GNU Lesser General Public
License along with the GNU C Library; if not, see
<http://www.gnu.org/licenses/>. */
#include <math.h>
#include <fenv.h>
#include <ieee754.h>
/* This implementation relies on long double being more than twice as
precise as double and uses rounding to odd in order to avoid problems
with double rounding.
See a paper by Boldo and Melquiond:
http://www.lri.fr/~melquion/doc/08-tc.pdf */
double
__fma (double x, double y, double z)
{
fenv_t env;
/* Multiplication is always exact. */
long double temp = (long double) x * (long double) y;
/* Ensure correct sign of an exact zero result by performing the
addition in the original rounding mode in that case. */
if (temp == -z)
return (double) temp + z;
union ieee854_long_double u;
feholdexcept (&env);
fesetround (FE_TOWARDZERO);
/* Perform addition with round to odd. */
u.d = temp + (long double) z;
if ((u.ieee.mantissa3 & 1) == 0 && u.ieee.exponent != 0x7fff)
u.ieee.mantissa3 |= fetestexcept (FE_INEXACT) != 0;
feupdateenv (&env);
/* And finally truncation with round to nearest. */
return (double) u.d;
}
#ifndef __fma
weak_alias (__fma, fma)
#endif
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