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56 lines
1.9 KiB
C
56 lines
1.9 KiB
C
/* Compute x * y + z as ternary operation.
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Copyright (C) 2010-2014 Free Software Foundation, Inc.
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This file is part of the GNU C Library.
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Contributed by Jakub Jelinek <jakub@redhat.com>, 2010.
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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 Lesser General Public
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License as published by the Free Software Foundation; either
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version 2.1 of the 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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Lesser General Public License for more details.
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You should have received a copy of the GNU Lesser General Public
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License along with the GNU C Library; if not, see
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<http://www.gnu.org/licenses/>. */
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#include <math.h>
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#include <fenv.h>
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#include <ieee754.h>
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/* This implementation relies on long double being more than twice as
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precise as double and uses rounding to odd in order to avoid problems
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with double rounding.
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See a paper by Boldo and Melquiond:
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http://www.lri.fr/~melquion/doc/08-tc.pdf */
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double
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__fma (double x, double y, double z)
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{
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fenv_t env;
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/* Multiplication is always exact. */
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long double temp = (long double) x * (long double) y;
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/* Ensure correct sign of an exact zero result by performing the
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addition in the original rounding mode in that case. */
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if (temp == -z)
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return (double) temp + z;
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union ieee854_long_double u;
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feholdexcept (&env);
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fesetround (FE_TOWARDZERO);
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/* Perform addition with round to odd. */
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u.d = temp + (long double) z;
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if ((u.ieee.mantissa3 & 1) == 0 && u.ieee.exponent != 0x7fff)
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u.ieee.mantissa3 |= fetestexcept (FE_INEXACT) != 0;
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feupdateenv (&env);
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/* And finally truncation with round to nearest. */
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return (double) u.d;
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}
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#ifndef __fma
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weak_alias (__fma, fma)
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#endif
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