]>
git.ipfire.org Git - thirdparty/glibc.git/blob - sysdeps/ieee754/ldbl-128/s_fma.c
1 /* Compute x * y + z as ternary operation.
2 Copyright (C) 2010-2020 Free Software Foundation, Inc.
3 This file is part of the GNU C Library.
4 Contributed by Jakub Jelinek <jakub@redhat.com>, 2010.
6 The GNU C Library is free software; you can redistribute it and/or
7 modify it under the terms of the GNU Lesser General Public
8 License as published by the Free Software Foundation; either
9 version 2.1 of the License, or (at your option) any later version.
11 The GNU C Library is distributed in the hope that it will be useful,
12 but WITHOUT ANY WARRANTY; without even the implied warranty of
13 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
14 Lesser General Public License for more details.
16 You should have received a copy of the GNU Lesser General Public
17 License along with the GNU C Library; if not, see
18 <https://www.gnu.org/licenses/>. */
23 #include <libm-alias-double.h>
25 /* This implementation relies on long double being more than twice as
26 precise as double and uses rounding to odd in order to avoid problems
28 See a paper by Boldo and Melquiond:
29 http://www.lri.fr/~melquion/doc/08-tc.pdf */
32 __fma (double x
, double y
, double z
)
35 /* Multiplication is always exact. */
36 long double temp
= (long double) x
* (long double) y
;
38 /* Ensure correct sign of an exact zero result by performing the
39 addition in the original rounding mode in that case. */
41 return (double) temp
+ z
;
43 union ieee854_long_double u
;
45 fesetround (FE_TOWARDZERO
);
46 /* Perform addition with round to odd. */
47 u
.d
= temp
+ (long double) z
;
48 if ((u
.ieee
.mantissa3
& 1) == 0 && u
.ieee
.exponent
!= 0x7fff)
49 u
.ieee
.mantissa3
|= fetestexcept (FE_INEXACT
) != 0;
51 /* And finally truncation with round to nearest. */
55 libm_alias_double (__fma
, fma
)