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5e908464 | 1 | /* Compute x * y + z as ternary operation. |
2b778ceb | 2 | Copyright (C) 2010-2021 Free Software Foundation, Inc. |
5e908464 JJ |
3 | This file is part of the GNU C Library. |
4 | Contributed by Jakub Jelinek <jakub@redhat.com>, 2010. | |
5 | ||
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. | |
10 | ||
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. | |
15 | ||
16 | You should have received a copy of the GNU Lesser General Public | |
59ba27a6 | 17 | License along with the GNU C Library; if not, see |
5a82c748 | 18 | <https://www.gnu.org/licenses/>. */ |
5e908464 JJ |
19 | |
20 | #include <math.h> | |
21 | #include <fenv.h> | |
22 | #include <ieee754.h> | |
f85a176f | 23 | #include <libm-alias-double.h> |
628d90c5 | 24 | #include <math-use-builtins.h> |
5e908464 JJ |
25 | |
26 | /* This implementation relies on long double being more than twice as | |
27 | precise as double and uses rounding to odd in order to avoid problems | |
28 | with double rounding. | |
29 | See a paper by Boldo and Melquiond: | |
30 | http://www.lri.fr/~melquion/doc/08-tc.pdf */ | |
31 | ||
32 | double | |
33 | __fma (double x, double y, double z) | |
34 | { | |
628d90c5 VG |
35 | #if USE_FMA_BUILTIN |
36 | return __builtin_fma (x, y, z); | |
37 | #else | |
5e908464 JJ |
38 | fenv_t env; |
39 | /* Multiplication is always exact. */ | |
40 | long double temp = (long double) x * (long double) y; | |
8ec5b013 JM |
41 | |
42 | /* Ensure correct sign of an exact zero result by performing the | |
43 | addition in the original rounding mode in that case. */ | |
44 | if (temp == -z) | |
45 | return (double) temp + z; | |
46 | ||
5e908464 JJ |
47 | union ieee854_long_double u; |
48 | feholdexcept (&env); | |
49 | fesetround (FE_TOWARDZERO); | |
50 | /* Perform addition with round to odd. */ | |
51 | u.d = temp + (long double) z; | |
52 | if ((u.ieee.mantissa3 & 1) == 0 && u.ieee.exponent != 0x7fff) | |
53 | u.ieee.mantissa3 |= fetestexcept (FE_INEXACT) != 0; | |
54 | feupdateenv (&env); | |
55 | /* And finally truncation with round to nearest. */ | |
56 | return (double) u.d; | |
628d90c5 | 57 | #endif /* ! USE_FMA_BUILTIN */ |
5e908464 JJ |
58 | } |
59 | #ifndef __fma | |
f85a176f | 60 | libm_alias_double (__fma, fma) |
5e908464 | 61 | #endif |